uiMivtKSi I y 0. 
 
 ILLINOIS LIBRARY 
 AT URBANA CHAMPAIGN 
 MATURAL HIST SURVEY 
 
':^^'^y^^^-:ih: 
 
 
 A 
 
 Distribution and Abundance 
 of Winter Populations of Bald Eagles in Illinois 
 
 Stephen P. Havera and Glen W. Kruse 
 
 Illinois Natural History Survey 
 Biological Notes 129, February 1988 
 
Cover Plioto: The bald easlc, Haluurlus kucocophalm. as photographed by Steven HoltyX'IREO. 
 
CONTENTS 
 
 DESCRIPTION 3 
 
 DISTRIBUTION 3 
 
 POPULATION LEVELS 3 
 
 LIFE HISTORY 4 
 
 Reproduction 4 
 
 Mortality 5 
 
 LEGAL STATUS 5 
 
 BALD EAGLES IN ILLINOIS 5 
 
 Historical Records, 1200-1950 5 
 
 Recent Records 6 
 
 Statewide Winter Bald Eagle Counts 6 
 
 INHS Eagle Surveys 9 
 
 Upper Mississippi River Region 11 
 
 Upper Central Mississippi River Region 11 
 
 Lower Central Mississippi River Region 12 
 
 Lower Mississippi River Region 14 
 
 Upper Illinois River Region 14 
 
 Central Illinois River Region 15 
 
 Lower Illinois River Region 15 
 
 Central and Southern Lakes Region 17 
 
 Northeast Lakes Region 17 
 
 Surface-mined Lakes Region 17 
 
 Loxt'er Kaskaskia River Region 17 
 
 Other Inventories 17 
 
 DISCUSSION OF CENSUS DATA 18 
 
 NIGHT ROOSTS 20 
 
 RECENT BALD EAGLE NESTING 20 
 
 BALD EAGLE MORTALITY 21 
 
 SUMMARY 22 
 
 ACKNOWLEDGEMENTS 23 
 
 APPENDIX 24 
 
 LITERATURE CITED 28 
 
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DISTRIBUTION AND ABUNDANCE OF 
 WINTER POPULATIONS OF BALD EAGLES IN ILLINOIS 
 
 Stephen P. Havera and Glen W. Kruse 
 
 The bald eagle {Haliaeetus leucocephalus) is the only 
 sea or fishing eagle that inhabits North America. 
 Seven additional members of this genus occur in other 
 parts of the world (Brown & Amadon 1968). Names 
 sometimes applied to the bald eagle include American 
 eagle, white-headed eagle, and Washington's eagle. 
 Immature bald eagles have been called black eagles 
 because of their dark color (Terres 1980). 
 
 In recent years, the numbers of bald eagles in 
 North America have rebounded frotn the critically 
 low levels that resulted from loss of habitat, illegal 
 shooting, and the widespread use of certain persistent 
 pesticides. Illinois is currently an important winter 
 area for bald eagles. 
 
 DESCRIPTION 
 
 Among the largest birds of North America, the 
 bald eagle has an average body length of 34 to 43 in 
 (85-109 cm) and a wingspan that is generally 6 to 7 
 ft (2.0—2.4 m). Robards (1967) reported wingspans of 
 78 to 93 in (1.98-2.36 m) for 39 eagles captured in 
 Alaska. As in most raptors, female bald eagles are 
 larger and heavier than males with the average weights 
 of females ranging between 10 and 14 lb (4.5—6.4 kg) 
 as compared with weights for males between 8 and 9 
 lb (3.6-4.1 kg) (Imler & Kalmbach 1955). Weights as 
 high as 16.5 lb (7.5 kg) were reported by R()l)ar(ls 
 (1967). Birds trapped in Minnesota weighed 8.() to 
 13.2 lb (3.9-6.0 kg) (Hennes 1985). 
 
 Although different immature and subadult |)lu- 
 mages of bald eagles occur, these plumages are mostly 
 dark brown with irregular patches of white on the 
 underside of the wings or elsewhere on the body 
 (Clark 1983) (Fig. 1). For the purposes of this study, 
 juvenile, immature, and subadult eagles were grouped 
 into the immature age class because subtle differences 
 in these plumages were diffuuit to discern during 
 aerial inventories. The bill of an iiimiaiure is brown. 
 the eyes are pale yellovv-giay, and ilu- feel .ut- lemon 
 yellow. Immature bald eagles are distinguished from 
 immature golden eagles by their larger heads, heavier 
 bills, and unfeathered legs (Terres 1980). 
 
 Thi.s paper is published by aiilhorily dI the Sialc i>l Illinois. It 
 is a contribution of the .Section ol VVildlile Researc h o( the Natural 
 History Survey. Dr. Stephen Havera is a Wildlilc K< oloj;ist at the 
 Survey field station in Havana, (ilen Kruse. lornurly an .Assistant 
 Research Biologist with the Survey, is now a I'rojed M.in.iK<i with 
 the Illinois Kndangered Species I'rotc-c tioii Uoaid in Springlield. 
 
 The recommendations ol two oi inoic oiilside ii lerecs are re- 
 quired before a manuscript is accepted lor public atinii in Hu)U)gifnl 
 
 At 4 to 5 years of age, bald eagles attain the familiar 
 adult plumage consisting of a dark brown body with 
 pure white head and tail (Fig. 2). The bills, eyes, and 
 feet of adult bald eagles are bright yellow (Terres 
 1980). 
 
 DISTRIBUTION 
 
 Two populations of bald eagles, the northern and 
 southern, have been described in North America. 
 Based on a slight difference in size, these populations 
 have been designated as subspecies with the not thern 
 population denoted as H. I. alascanus and the southern 
 group as H. I. leucocephalus. For purposes of manage- 
 ment and legal protection, these two populations are 
 treated as one because of overlapping ranges in the 
 nonbreeding season. 
 
 Historically, the northern population of bald 
 eagles bred from Bering Island, the Aleutian Islands, 
 northwestern Alaska, Mackenzie, Manitoba, central 
 Ontario, southeastern Quebec, Labrador, and the 
 coasts of Newfoundland southward to southern Ore- 
 gon, Idaho, Wyoming, Colorado. South Dakota, Min- 
 nesota, Wisconsin, Michigan, Ohio, Pennsvlvania, 
 New Jersey, and Marylantl. Breeding still occins in 
 Maine, the Chesapeake Bay area, the Upper Peninsula 
 of Michigan, northern Wisconsin. Mintiesota. north- 
 ern Idaho, Oregon, Washington, Alaska. Saskatche- 
 wan, Manitoba, and northern Ontario (F^ans 1982). 
 
 The southern population once bred from north- 
 ern California southward to Ixjth coasts of Baja 
 California, central Arizona, New Mexico, western 
 Nevada, and southern Utah, and from northern 
 Texas, Oklahoma. Missouri, Iowa, southern Illinois, 
 western Keniuckv, and Virginia south to the C.ulf 
 Coast of Florida. Iliis population now breeds primar- 
 ily in Florida with some nesting occurring in 
 Louisiana, Texas, California, and Arizona (Evans 
 1982). 
 
 During the nonbreeding season, the northern 
 birds c an be found from .Alaska, northern Mackenzie, 
 southern Ontario, Quelx-c , and souihern Nova Scotia 
 to the southern United .States. Some southern birds 
 may wander northward in llieii iioiibreeding season 
 (Evans 1982). 
 
 POPULATION LEVELS 
 
 The U.S. Fish .uid Wildlife .Service (USFWS) and 
 private conservation organizations have esiim.iied the 
 mmiber of bald eagles present in the 48 c onligiioiis 
 
Illinois Natural History Survey Biological Notes 
 
 No. 129 
 
 Fig. 1.— Immature bald eagle in 
 night (Photo by David L.Fischer). 
 
 Fig. 2.— Adult bald eagle search- 
 ing for prey (Photo by David L. 
 Fischer). 
 
 States during winter. The difficulty of coordinating a 
 census over such a large area has resulted in counts 
 that provide only an index to actual population levels. 
 
 Nationwide bald eagle censuses have shown a 
 dramatic increase since the late 1970s (Table 1). The 
 increase is attributed partially to more effective 
 counts. Until 1976, counts were the result of incidental 
 eagle sightings during a USFWS January waterfowl 
 inventory. In 1979, the National Wildlife Federation 
 (NWF) organized an annual midwinter bald eagle sur- 
 vey. Thousands of persons are currently involved in 
 the enumeration of bald eagles. 
 
 Although variation in geographical coverage of 
 the midwinter bald eagle surveys among years makes 
 accurate counts difficult, bald eagles appeared to have 
 reached their highest number of 13,825 in 1982 
 (Table 1). Millsap (1986) noted that a reasonable esti- 
 mate of the midwinter population of bald eagles for 
 the lower 48 states during the early 1980s was 14,000- 
 22,000 birds. A decline in numbers observed on the 
 midwinter survey has occurred since 1982 (Table 1). 
 
 Table 1. — Number of bald eagles in the contiguous United States 
 during January, 1961-1986. 
 
 Year 
 
 Number Counted 
 
 Reference 
 
 1961 
 
 3.642 
 
 Spruntand Ligas 1963 
 
 1962 
 
 3,807 
 
 Spruntand Ligas 1963 
 
 1963 
 
 3.547 
 
 Spruntand Ligas 1963 
 
 1971 
 
 2,490 
 
 USFWS unpublished'' 
 
 1972 
 
 2,668 
 
 USFWS unpublished = 
 
 1973 
 
 2,986 
 
 USFWS unpublished^ 
 
 1974 
 
 3,553 
 
 USFWS unpublished" 
 
 1975 
 
 3,580 
 
 USFWS unpublished'' 
 
 1976 
 
 4,478 
 
 USFWS unpublished = 
 
 1979 
 
 9,815 
 
 NWF (1985) 
 
 1980 
 
 13,046 
 
 NWF(1985) 
 
 1981 
 
 13,689 
 
 NWF(I985) 
 
 1982 
 
 13,825 
 
 NWF(1985) 
 
 1983 
 
 12,098 
 
 NWF(1985) 
 
 1984 
 
 11,819 
 
 NWF(1985) 
 
 1985 
 
 10,985 
 
 NWF (1985) 
 
 1986 
 
 8,318 
 
 NWF'' 
 
 'Stcenhof (1976). 
 'Personal communication. 
 
 The 1985 estimate of the breeding population of 
 bald eagles in the United States was approximately 
 5,000 pairs with about 1,770 pairs nesting in the con- 
 terminous 48 states and the remainder in Alaska 
 (USFWS 1986). Approximately 500 nesting pairs oc- 
 curred in the lower 48 states in the early 1960s (NWF 
 1987). Braun et al. (1975) suggested that the down- 
 ward trend in the reproductive success of bald eagles 
 that resulted from persistent pesticides had slowed 
 dramatically by 1975. Surveys of the breeding popu- 
 lation of bald eagles conducted in 1982 and again in 
 1985 indicated that the number of breeding pairs in 
 the lower 48 states increased about 6% per year during 
 this period (USFWS 1986). 
 
 LIFE HISTORY 
 
 Reproduction 
 
 Most eagle nests are built in trees from 10 to 150 
 ft (3-46 m) above the ground (Terres 1980). Nests 
 are made of sticks, mosses, pine needles, grasses, and 
 feathers and are the largest nests built by a single pair 
 of birds, commonly 6 ft (1.8 m) wide and 6 ft (1.8 m) 
 deep and occasionally as much as 20 ft (6.1 m) wide 
 and 9.5 ft (2.9 m) deep (Brown 1977). Both sexes 
 participate in nest building. The same nest may be 
 used for 10 to 30 years with new material added every 
 year (Brown 1977). 
 
 One to three, usually two, dull-white eggs are laid 
 during November to January in Florida and during 
 March to May in the northern range (Terres 1980). 
 Both sexes incubate the eggs, but the female assumes 
 the greater share of the incubation duty, which lasts 
 for approximately 35 days (Brown 1977). Incubation 
 begins with the laying of the first egg: therefore, the 
 sequential hatching of eggs results in chicks of differ- 
 ent sizes. Smaller and weaker chicks often die from 
 starvation or are killed and eaten bv the older, larger 
 chicks (Terres 1980). Newly hatched bald eagle chicks 
 are covered with white or gray down, which is replaced 
 by thicker gray down at 2 to 3 weeks of age. Feathers 
 begin to appear at 4 to 5 weeks, ^'oung birds Hedge 
 in 72 to 75 days. 
 
Febnjary1988 
 
 Havera and Kruse: Winter Populations of Bald Eagles 
 
 Mortality 
 
 Mortality of subadult bald eagles is high. Sherrod 
 et al. (1976) found that mortality of subadult bald 
 eagles in Alaska was approximately 90% through their 
 first 3 years. Death resulted from limited food supply 
 and starvation complicated by the lower rate of success 
 as predators for subadult eagles. Mortality for adults 
 appeared to be low and ranged from 5 to 10% per 
 year (Sherrod et al. 1976). The longevity record for 
 a banded wild bald eagle is 2 1 years 1 1 months at the 
 time of recapture (Cain 1986). 
 
 The causes of mortality among bald eagles are 
 closely monitored. In recent years, the Patuxent 
 Wildlife Research Center and the National Wildlife 
 Health Laboratory (NWHL) have been responsible 
 for determining the causes of death from eagle car- 
 casses found in the United States. Between 1963 and 
 1984, 1,429 bald eagle carcasses were submitted to 
 the NWHL for necropsy. Although the results of the 
 postmortem examinations (Table 2) may not repre- 
 sent the actual proportional causes of mortality be- 
 cause of sampling bias, the data serve to demonstrate 
 the most common known causes of mortality (NWHL 
 1985). 
 
 Table 2. — Summary of causes of death of 1,429 bald eagles, natlon- 
 widefrom 1963-1984 (National Wildlife Health Laboratory 1985). 
 
 CauseofDeath Nutr 
 
 iber of Deaths 
 
 Percent of Total 
 
 Gunshot 
 
 329 
 
 23.0 
 
 Trauma (excluding gunshot, 
 
 
 
 electrocution, and trapping) 
 
 301 
 
 21.1 
 
 Electrocution 
 
 130 
 
 9.1 
 
 Emaciation 
 
 110 
 
 7.7 
 
 Poisoning (excluding lead) 
 
 75 
 
 5.2 
 
 Lead poisoning 
 
 83 
 
 5.8 
 
 Trapping 
 
 68 
 
 4.8 
 
 Disease 
 
 31 
 
 2.2 
 
 Other 
 
 43 
 
 3.1 
 
 No diagnosis 
 
 259 
 
 18.0 
 
 At least one of the 1,429 eagles examined was 
 found in each state except Hawaii and New Hamp- 
 shire. Some states reported numerous incidents of 
 eagle mortality, including Alaska (228), Wisconsin 
 (159), Minnesota (120), and Florida (107). Twenty- 
 five or more dead eagles were found in each of 20 
 states (NWHL 1985). 
 
 Of the 158 deaths attributed to poisoning (Table 
 2), 83 (52.5%) were a result of lead poisoning. All 
 available evidence indicates that bald eagles are ex- 
 posed to the toxic effects of lead when they feed on 
 waterfowl that have lead shot embedded in their fiesh 
 or present in their digestive tracts (NWHL 1985). 
 Many eagles winter on wildlife refuges where (rip- 
 pled, sick, and dead waterfowl are a major portion of 
 the diet (Sabine & Klimstra 1985, Hennes 1985, Keis- 
 ter et al. 1987). 
 
 (Confirmations of lead poisoning as a substantial 
 mortality factor for bald eagles have prompted the 
 enactment of protective regulations. As a result of a 
 lawsuit filed by the NWF, a federal judge ordered the 
 
 closing of 30 counties in 8 states to waterfowl hunting 
 during the 1985-1986 season unless nontoxic shot 
 was used (U.S. Depi. of Interior 1985). The USFWS 
 expanded the prohibition of lead shot to include a 
 total of 173 counties in 26 states for the 1986-1987 
 waterfowl hunting season (U.S. Dept. of Interior 
 1986) and has proposed a nationwide ban on the use 
 of lead shot for the hunting of waterfowl by the 1991- 
 1992 season (USFWS 1986). Such restrictions on the 
 use of lead shot eventually will reduce the availability 
 of lead to bald eagles and the subsequent sublethal 
 and lethal effects that result from ingestion of lead 
 pellets. 
 
 LEGAL STATUS 
 
 The bald eagle has been a protected species in the 
 United Statessince the establishment of the Bald Eagle 
 Protection Act in 1940. The act provides a fine of up 
 to $10,000 and a prison term of up to 2 years for a 
 violator and prohibits the taking, possession, sale, pur- 
 chase, barter, offer to sell, transport, and export or 
 import of any bald eagle, alive or dead, including any 
 part, nest, or egg, unless allowed by permit. 
 
 Other federal laws that protect the bald eagle in- 
 clude the Migratory Bird Treaty Act, the Endangered 
 Species Act, the Lacey Act, and the Airborne Hunting 
 Act. The bald eagle is listed as endangered in 43 states 
 and threatened in 5 other states (Mendoza 1984). 
 
 BALD EAGLES IN ILLINOIS 
 
 Historical Records, 1200-1950 
 
 Bald eagles have been present in what is now Il- 
 linois for thousands of years. The first documented 
 presence of eagles dates back 400 to 800 years based 
 upon the remains of at least 16 bald eagles identified 
 by Parmalee (1958) from Indian burial sites at 
 Cahokia. The predominance of bones associated with 
 the primary wing feathers suggested that eagle feath- 
 ers were used for symbolic or ceremonial purposes. 
 
 Reports of bald eagle sightings in Illinois during 
 the late nineteenth and early twentieth centuries are 
 mostly anecdotal accounts in newspapers and or- 
 nithological journals. Apparently, the sighting of an 
 eagle in most parts of the stale during this period was 
 of sufficient rarity to be tonsidered newsworthy. 
 
 Ridgway (1889) listed the bald eagle as "a siunmer 
 resident of general distribution" that was "more or 
 less connnon" along the larger waterways. The men- 
 tion of siniuner residency suggests that bald eagles 
 nested in Illinois in the late 1800s. 
 
 Only a few years after Ridgway's account was pub- 
 lished, (iault (189()) expressed surprise at seeing a 
 bald eagle near Melrose Park in CCook County. He 
 (onsidered the eagle a "rare transient" and was par- 
 tidilarly surprised lo see the bird on April 28, an 
 imustiallv late dale for eagles to Ih" in thai area. 
 
 The first bald eagle reported on the .\udubon 
 Christmas bird ct)unt was in 1914 al Hinsdale, Illinois 
 (Anon. 1915). Two bald eagles were seen and killed 
 
linois Natural History Survey Biological Notes 
 
 near Rantoul in Champaign County in May of 1918. 
 The previously reported sighting of eagles in that area 
 was in 1915 (Ekblaw 1918). 
 
 Pellett (1927) reported that he saw two or more 
 bald eagles frequently on the Mississippi River be- 
 tween Keokuk, Iowa, and Warsaw, Illinois, during the 
 winter of 1925—1926. He estimated that eight eagles 
 were killed by hunters in that area during the same 
 winter. 
 
 The bald eagle appeared rarely in the Chicago 
 region during the late 1920s. Ford et al. (1934) re- 
 ported sightings in February 1924, December 1928, 
 and January 1930. 
 
 The Ohio and Wabash river valleys have generally 
 been considered unimportant as eagle habitat, but 
 Bonnell (1935) reported scattered sightings and shoot- 
 ings of eagles in these areas between 19 10 and 1934. 
 
 Musselman (1942) noted the killing of at least 1 1 
 eagles in the vicinity of Lock and Dam 19 at Keokuk 
 on the Mississippi River between 1 929 and 1 938. Mus- 
 selman often sighted 12 to 18 eagles in this area in 
 the late 1930s. The mayor of Henry in Marshall 
 County shot and killed an immature bald eagle in 
 November 1939 near Henry (Barnes 1939). 
 
 Bellrose (1944) reported nesting by bald eagles 
 near Henry every year from 1935 to 1940 and at 
 Horseshoe Lake in Alexander County from 1941 to 
 1943. Until that time, nesting had not been reported 
 in Illinois since 1915, when a pair nested in Piatt 
 County. These were possibly the same birds reported 
 from Champaign County by Ekblaw (1918). 
 
 Observations by Musselman indicate that increas- 
 ing numbers of eagles utilized the Mississippi River 
 near Lock and Dam 19 during the 1940s. Twenty-five 
 to 30 eagles often were seen during the winter of 
 1944-1945 (Musselman 1945) and as many as 83 birds 
 were sighted in the winter of 1947—1948 (Musselman 
 1949). 
 
 There was also an increase in the numbers of 
 eagles sighted near the Illinois River. Yeager (1950) 
 observed at least 12 eagles at Chautauqua National 
 Wildlife Refuge in January 1943. 
 
 Recent Records 
 
 Historically, the bottomlands near the confluences 
 of the Missouri, Ohio, and Mississippi rivers were 
 major nesting areas for bald eagles (USFWS 1986), 
 and the large rivers and wetlands in and adjoining 
 Illinois have served as important winter habitat. De- 
 clines in the continental population caused by such 
 factors as habitat destruction, illegal shooting, increas- 
 ing human use of formerly remote areas, and, more 
 recently, pesticide contamination that resulted in poor 
 reproduction (Evans 1982) have been reflected in the 
 small numbers of eagles observed in Illinois from the 
 late 1800s until about the inid-19()0s. 
 
 Currently, however, the Mississippi River valley 
 from southern Minnesota to southern Illinois is an 
 important winter area for bald eagles (L'SFVY'S 1986). 
 
 Illinois, Missouri, and Arkansas also host several 
 hundred bald eagles each winter (USFWS 1986). 
 Millsap (1986) analyzed the geographic distribution 
 of wintering bald eagles counted during the 1979 to 
 1982 midwinter surveys (Fig. 3). Millsap (1986:437) 
 found that over 95% of the bald eagles observed dur- 
 ing the midwinter surveys occurred west of a line from 
 Lake Michigan to the Mississippi delta and that more 
 than 30% of the sightings occurred along and adjacent 
 to the Mississippi, Illinois, and Missouri rivers (Fig. 3). 
 
 Several major migratory populations of bald eagles 
 have been identified from analysis of band recoveries 
 (Fig. 4) (USFWS 1 986). Illinois hosts eagles principally 
 associated with the Western Great Lakes population. 
 The banding analysis revealed that bald eagles that 
 use common winter sites in the Mississippi River valley 
 originate from widely separated breeding areas in 
 Michigan, Wisconsin, Minnesota, and Ontario (Fig. 4). 
 
 Statewide Winter Bald Eagle Counts. In the late 
 1950s, the decline in eagle populations stimulated in- 
 terest in monitoring the numbers of eagles wintering 
 along the Illinois and Mississippi rivers as an indication 
 of population status. An ongoing program of aerial 
 surveys of migrating waterfowl was begun by the Il- 
 linois Natural History Survey (INHS) in 1948 and 
 provided the means to monitor bald eagle populations 
 in the floodplains of the Mississippi and Illinois rivers. 
 In 1957, Frank Bellrose began to count bald eagles 
 in addition to waterfowl on the annual winter inven- 
 tory conducted in January. This annual count of bald 
 eagles was continued for most years until 1972, when 
 the waterfowl inventory program was expanded to 
 include other areas of Illinois and Robert Crompton 
 made eagle counts a part of each aerial waterfowl 
 census. 
 
 In 1961, a second annual winter eagle count was 
 coordinated by Elton Fawks of East NIoline. Those 
 counts usually included the entire Upper Mississippi 
 River, but separate data were maintained for the Il- 
 linois portion of the river. Additional eagle census 
 information has been compiled by the Illinois .\udu- 
 bon Society as a result of their annual Christmas bird 
 count. 
 
 The numbers of eagles sighted on the three winter 
 counts are presented in Table 3. Inventories bv the 
 INHS covered the Illinois River from Spring N'allev 
 to Naples and the Mississippi River from Rock Island 
 to Grafton (including the lower 26 miles of the Illinois 
 River) for all years listed. The Illinois River from 
 Channahon to Spring N'allev was inventoried from 
 1975 to 1985. The Mississippi Rivei from St. Louis. 
 Missouri, to Cairo was censused from 1973 to 1986 
 and from Dubuque, Iowa, to Rock Island from 1981 
 to 1983. Counts were done in these areas as part of 
 the winter waterfowl inventorv and were completed 
 between 2 and 18 januarv each vear. Data from these 
 INHS inventories were included in the NWF mid- 
 winter bald eagle survev (Table 1). 
 
 Total eagles counted hv the INHS during Januarv 
 ranged from 63 in 1960 to 1,217 in 1986 (Table 3). 
 
February 1988 HaveraandKruse: Winter Populations of Bald Eagles 
 
 125° 120° 115° 110° 105° 100° 95° 90° 85° 80° 
 
 75° 
 
 70° 
 
 45« 
 
 40° 
 
 35= 
 
 30° 
 
 25° 
 
 45° 
 
 40° 
 
 35° 
 
 30° 
 
 25° 
 
 115° 110° 105° 100° 95° 90° 85° 80° 
 
 m. :'. -DisiTilniliniis ol tlic avcniijf niimhir (il h.ild lanlcs ohsitMil (mt coimi duniiK ilic iiuiluiiilci siirvcvs. HITD-HISl' (Mills.ip Hmfi: 
 ipMiKlil. 1 li>- Wikllilc Socifiy). 
 
 A majority of eagles seen during the winter inventory 
 was associated with the Mississippi River floodplain. 
 Since 1973, nunil)ers of eagles tensused in Januaiv 
 along the Illinois River usually ranged between 100 
 and 300, with a maximum of 383 observed in l'.)8(). 
 Ihe percentage of all eagles censused by the I NHS 
 during January that were immatures ranged between 
 16.5 and 46.5% (Table 3). In a majority of the years, 
 the percentage of immature eagles varied between 30 
 and 37%. Southern (1963) cautioned, however, 
 against using the proportion of immatures to adult 
 eagles wintering in the Mississippi Valley bordering 
 Illinois as a realistic estimate o( leprochu live suctess. 
 Millsap (1986:436) re])orted that the jjercfiitage of 
 imiTiature bald eagles observed on the midwintei sur- 
 vey from 1979 to 1982 varied between 32.7 and 4 1 .2% . 
 Sprunt (1965) reported that estimates of inimatuie 
 bald eagle age ratios ranged between 21.(j and 26.5% 
 from surveys (ondiKterl by the National AudulK)n 
 Society from 1961 to 1963. 
 
 The counts compiled by Elton Fawks were both 
 aerial and ground (ounts (Table 3). F.ach count in- 
 ( hided the Mississippi Ri\ei from I)ubu(|ue to "below 
 St. Louis," the Illinois Rivei, and vaiying numbers 
 and combinations of refuges and reservoirs. The Mis- 
 sissippi River from (Irafton to C.aiio was added in 
 1976. The 1982 count also included the Fox. Wabash, 
 Rock, and Ohio rivers. Fiom 1961 to 1978, the count 
 was ma<le fluting the second or third week of Feb- 
 ruary. Since 1979, when this (ount became part of 
 the midwinter l)ald eagle sur\e\ sponsored by the 
 NVVT. it has been conducted duiing early to mid- 
 |aniiaiy. Tawks' counts of bald e.igles ranged tiom 
 414 in J9(i4 to 1,104 in 1979 (Table 3). 
 
 Illinois ,'\udul)on .Societ) Ohiislm.ts biid counls, 
 takc-n in late Dec c-niber eac h year, are ground counts 
 made from cars and on foot. These counts probably 
 cover more scjuare miles of the state than the aerial 
 inventories desc ribed al>ove. but thev do not concen- 
 tiatc- on .iic-.is neai large rivers where bald eagles are 
 
Illinois Natural History Survey Biological Notes 
 
 No. 129 
 
 Southeast 
 Alaska 
 
 Northwest 
 Interior 
 
 Maine/ 
 Nova Scotia 
 
 I 
 
 \\ Florida 
 
 Breeding Area 
 Represented by Bandings 
 
 Fig. -4. -Major migraioi \ |)"l) 
 Scrviii- 1986) 
 
 Oilohii lliniii.jh M.mli li.iiul icmM-rics (IS. lisli .iii.l U ildlile 
 
 most likely to occur. Areas covered in the Christmas 
 bird counts are generally those surroimding the loca- 
 tion of local Audubon Society chapters. Bald eagles 
 observed on the Christmas bird counts ranged from 
 256 in 1974 to 767 in 1986 (Table 3). 
 
 Differences in dates of counts, areas coveted, skills 
 of observers, and weather conditions and the emphasis 
 placed on counting eagles as opposed to other species 
 create variability among the inventories (Table !5). 
 Whereas counts for a single year vary widely, there 
 
 are several instances when the changes between years 
 are similar. Kxamiiiation of eagle numbers in Table 
 3 reveals that both the INHS and Fawks inventories 
 show intreases from 1961 to 1962, decreases from 
 1962 through 1964, and increases fiom 1964 to 1965 
 and from 1977 tiirough 1979. Such similarities in 
 trends suggest that patterns of changes in eagle nimi- 
 bers in Illinois are real and demonstrate the impor- 
 tance of more than one type of amnial count. 
 
 Moving .3-year averages of the aiuuial winter 
 
February 1988 
 
 Havera and Kruse: Winter Populations of Bald Eagles 
 
 Table 3. — Winter bald eagle counis (ondii 
 couiu, 1957-1987. 
 
 (1 \n the lllin()i> Natural Hisiorv Survey. KUon hawks, and the .Audubon Christmas bird 
 
 
 
 INHS 
 
 
 
 Fawk 
 
 s'' 
 
 
 
 Audubon''''- 
 
 
 ^ear 
 
 .\duli 
 
 liiiinalure 
 
 lolal 
 
 .•\(luli 
 
 Itninaturc 
 
 L'nascd 
 
 lolal 
 
 .^duh 
 
 Immature 
 
 Unaged 
 
 total 
 
 19.-) 7 
 
 
 
 359 
 
 
 
 
 
 
 
 
 
 19.59 
 
 
 
 207 
 
 
 
 
 
 
 
 
 
 1960 
 
 
 
 (i3 
 
 
 
 
 
 
 
 
 
 1961 
 
 142 
 
 30 
 
 172 
 
 365 
 
 51 
 
 1 
 
 417 
 
 
 
 
 
 1962 
 
 143 
 
 44 
 
 187 
 
 417 
 
 62 
 
 29 
 
 508 
 
 
 
 
 
 1963 
 
 108 
 
 64 
 
 172 
 
 331 
 
 91 
 
 7 
 
 429 
 
 
 
 
 
 1904 
 
 68 
 
 30 
 
 98 
 
 226 
 
 58 
 
 130 
 
 414 
 
 
 
 
 
 196-) 
 
 ".■) 
 
 52 
 
 127" 
 
 420 
 
 160 
 
 44 
 
 624 
 
 
 
 
 
 1966 
 
 
 
 
 486 
 
 122 
 
 51 
 
 659 
 
 
 
 
 
 1967 
 
 
 
 
 485 
 
 175 
 
 28 
 
 688 
 
 
 
 
 
 196H 
 
 84 
 
 37 
 
 121'' 
 
 415 
 
 174 
 
 50 
 
 639 
 
 
 
 
 
 1969 
 
 
 
 
 391 
 
 261 
 
 3 
 
 655 
 
 
 
 
 
 1970 
 
 112 
 
 76 
 
 188 
 
 
 
 
 
 
 
 
 
 1971 
 
 100 
 
 40 
 
 140 
 
 406 
 
 159 
 
 11 
 
 576 
 
 
 
 
 
 1972 
 
 75 
 
 19 
 
 94 
 
 .562 
 
 302 
 
 31 
 
 895 
 
 158 
 
 95 
 
 29 
 
 282 
 
 1973 
 
 364 
 
 175 
 
 539 
 
 529 
 
 231 
 
 14 
 
 774 
 
 211 
 
 115 
 
 14 
 
 340 
 
 1974 
 
 398 
 
 153 
 
 551 
 
 413 
 
 128 
 
 8 
 
 549 
 
 140 
 
 113 
 
 3 
 
 2.56 
 
 1973 
 
 365 
 
 201 
 
 566 
 
 519 
 
 274 
 
 32 
 
 825 
 
 304 
 
 182 
 
 110 
 
 596 
 
 1976 
 
 489 
 
 270 
 
 759 
 
 459 
 
 214 
 
 33 
 
 706 
 
 287 
 
 269 
 
 6 
 
 562 
 
 1977 
 
 327 
 
 144 
 
 471 
 
 508 
 
 264 
 
 29 
 
 801 
 
 405 
 
 252 
 
 11 
 
 668 
 
 1978 
 
 369 
 
 166 
 
 535 
 
 69() 
 
 219 
 
 52 
 
 967 
 
 503 
 
 •247 
 
 11 
 
 761 
 
 1979 
 
 410 
 
 203 
 
 613 
 
 1,018 
 
 356 
 
 30 
 
 1.404 
 
 244 
 
 149 
 
 10 
 
 403 
 
 1980 
 
 514 
 
 288 
 
 802 
 
 931 
 
 4()(i 
 
 57 
 
 1 ,394 
 
 384 
 
 203 
 
 7 
 
 594 
 
 1981 
 
 454 
 
 304 
 
 758 
 
 
 
 
 
 228 
 
 153 
 
 5 
 
 386 
 
 1982 
 
 517 
 
 271 
 
 788 
 
 888 
 
 380 
 
 28 
 
 1 .296 
 
 211 
 
 128 
 
 3 
 
 342 
 
 1983 
 
 365 
 
 178 
 
 543 
 
 
 
 
 
 292 
 
 256 
 
 17 
 
 565 
 
 1984 
 
 613 
 
 317 
 
 930 
 
 
 
 
 
 316 
 
 218 
 
 3 
 
 537 
 
 198.5 
 
 404 
 
 247 
 
 651 
 
 
 
 
 
 420 
 
 235 
 
 12 
 
 667 
 
 1986 
 
 779 
 
 438 
 
 1.217 
 
 
 
 
 
 443 
 
 313 
 
 11 
 
 767 
 
 1987 
 
 368 
 
 201 
 
 569 
 
 
 
 
 
 
 
 
 
 ■'Kawks (1983). 
 
 ''Struihcrs (1973. 1974, 1975, 1976, \'.r, 
 'Stroyls (1981, 1982, I9H3, 1984, 1985. 
 ' Incomnlele count. 
 
 7, 1978, 1979, 1980). 
 1986, 1987). 
 
 counts are presented in Figure 5. Each of the three 
 inventories shows a general trend toward higher num- 
 bers in recent years. As noted by Fawks ( 198S), weatli- 
 er and other factors that interfere with ac( urate counts 
 are of lesser importance if data interpretation is based 
 on multi-year averages rather than one-year totals, 
 (founts by the Illinois Audubon Society were probably 
 also influented by changes in geographical coverage 
 between years. 
 
 INHS Eagle Surveys. The most extensive record 
 o( bald eagle populations in Illinois was compiled by 
 the INHS. Kagles were toiuited onte eat h year in 
 I'C)?, H)59 to \9(]5, 1968, 1970, and 1971 (Table :<). 
 Sinte I97'2, several counts were made each year in 1 1 
 regions of the slate (Table 4, Fig. 6) and provide de- 
 tailed information. Riverine regions inventoried in- 
 cluded the river pioj^er and accom])anying wetlands 
 in the iloodplain. (Censuses conducted in the Missis- 
 sippi River iloodplain included eagles seen in Iowa 
 and Missouri. Kach region wasdi\idc-d into a muiiber 
 of census areas for recording data. Individual .ueas 
 inc iuded river segments def'med by pioiniiicni lanil- 
 iti.irks, lakes, bays, marshes, sloughs, oi ollit-i wetland 
 aieas. The census aieas included in each ic-gion ate 
 listed in the Appendix. The numbei ol miles of river 
 
 and the area of wetlands in each riverine region are 
 presented in Table 5. 
 
 The number of years in whic h aerial censuses were 
 taken in a region and the niutiber of flights made 
 each year were dependent upon availability of funds 
 
 1500 
 1200 
 1100 
 1000 
 
 o 800 
 
 "" 700 
 
 $ 600 
 
 O 
 
 •" 500 
 
 <00 
 
 1- INHS 
 ) - FAWKS 
 i - AUDUBON 
 
 1977, 
 1986, 
 
 I960 IMZ IM4 !««« IMS l«70 1972 1*74 1976 1978 IMO 1962 19*4 19*6 
 YEAR 
 
 1 liiii-vrai m<>\iii){ .ivei.igrs ol wiiiKi eagle ciHiiUs ill II- 
 hoiii Illinois N.iim.il llislory Siirxcy data, lawks ( 1983), and 
 linois .\iidulM.n So(ici\ (Siniiliers 1973, 1974, 1975. 1976. 
 
 1978. 1979. 1980; Siioyls 1981, 1982. 1983. 1984. 198.5, 
 
 1987). 
 
Illinois Natural History Survey Biological Notes 
 
 No. 129 
 
 Table 4. — Regions aerially iinentoried for bald eagles by the INHS and the Irequeno, approximate period, and years of censuses in 
 each region. 
 
 Region 
 
 Upper Mississippi Riyer (Dubuque— Interstate 80) 
 Upper Central Mississippi Riyer (Moline— Keokuk) 
 Lower Central Mississippi Riyer (Keokuk-Alton, 
 
 lower 26 miles of Illinois Riyer) 
 Lower Mississippi Riyer (St. Louis-Cairo) 
 Upper Illinois River (Morris-Spring Valley) 
 Central Illinois Riyer (Spring Valley-Lower Peoria Lake) 
 Lower Illinois River (Pekin Lake-Naples) 
 Surface-mined Lakes (Fulton, Knox counties) 
 Northeast Lakes (natural lakes, cooling lakes, 
 
 reservoirs in Cook, De Kalb, Grundy. Lake, 
 
 La Salle. McHenry, Will counties) 
 Central and Southern Lakes (Reservoirs: Carlyle, 
 
 Rend, Shelbyville, Springfield. Cooling lakes: 
 
 Baldwin, Clinton, Coffeen, Newton, Sangchris) 
 Lower Kaskaskia River (Fayetteville-Chester) 
 
 ■'Period lengths varied due to availability of llight tunds 
 
 and on weather (Table 4). The number of aerial inven- 
 tories, mean number of bald eagles observed per in- 
 ventory, and maximum number of eagles seen on a 
 single inventory for each census area for all census 
 years are presented in the Appendix. The mean 
 number of bald eagles sighted per inventory flight 
 for all years was used as the indicator level of eagle 
 
 Frequency of 
 Inventories 
 
 .•\pproxinialc 
 Inventory Period'' 
 
 Biweekly 
 
 October- March 
 
 1980-1983 
 
 Weekly 
 
 Sept.-Dec, Jan., Feb.-April 
 
 I972-I986 
 
 Weekly 
 Biweekly 
 
 Sept-Dec. .Jan.. Feb.-April 
 October- April 
 
 1972-1986 
 1972-1986 
 
 Biweekly 
 Weekly 
 Weekly 
 Biweekly 
 
 September- April 
 
 Sept.- Dec. .Jan., Feb.- .April 
 
 Sept.-Dec. .Jan., Feb.-April 
 
 October- March 
 
 1976-1985 
 1972-1986 
 1972-1986 
 1980-1985 
 
 Biweekly 
 
 Biweekly 
 Biweekly 
 
 September- .•\pril 
 
 October- April 
 October- April 
 
 1972-1986 
 1982-1986 
 
 Upper Cenlfal Mississippi "^ Sufface-mired 
 
 Lower Central Mississippi 
 
 Northeast Lakes 
 
 Central and Southern Lakes 
 
 use for a given area. The number of inventories and 
 the mean number of eagles observed per inventorv 
 were based on the period between the first sighting 
 of a bald eagle in the fall of each year and the last 
 eagle sighting the following spring, and not the entire 
 census period from fall through spring. This proce- 
 dure appropriately concentrated on the period when 
 eagles were present in the various regions. The arrival 
 and departure dates of bald eagles in Illinois vary 
 each year as a result of differences in weather, freeze- 
 ups, and other unpredictable phenomena of nature. 
 Differences in the length of the inventory period 
 and the number of years of censuses should be taken 
 into consideration when making comparisons in 
 values for the mean number of eagles coimted per 
 inventory among regions (Table 4). For instance, the 
 Upper Mississippi River Region was inventoried din- 
 ing 1980-1983 as compared with 1972-1986 for the 
 other Mississippi River regions. Bald eagles ha\e gen- 
 erally increased in Illinois since 1972 (Table 3) and a 
 mean value for the number seen per inventory in 
 more recent years (1980-1983) mav pn)vide a differ- 
 ent value than a mean calculated on data from 1972- 
 
 Table 5. — River miles and wet 
 
 and area inch 
 
 ded 
 
 in riverine census 
 
 regions. 
 
 
 
 
 
 
 
 R 
 
 vcr Mile 
 
 ,;j 
 
 Wetland Area'' 
 
 Region 
 
 mi^ 
 
 km- 
 
 Upper Mississippi River 
 
 
 8.5.4 
 
 
 122.9 
 
 318.3 
 
 Upper Central Mississippi Ri\e 
 
 
 i;n.:i 
 
 
 168.5 
 
 436.4 
 
 LowerC'entral Mississippi Rive 
 
 
 187.1 
 
 
 265.3 
 
 687.1 
 
 Lower Mississippi River 
 
 
 202.9 
 
 
 242.2 
 
 627.3 
 
 Upper Illinois River 
 
 
 57.0 
 
 
 24.6 
 
 63.7 
 
 Central Illinois River 
 
 
 57.8 
 
 
 82.4 
 
 213.4 
 
 Lower Illinois River 
 
 
 l:l6.2 
 
 
 154.6 
 
 400.4 
 
 Lower Kaskaskia River 
 
 
 :«).o 
 
 
 22.5 
 
 58.3 
 
 Tig. 6. -Regions ol llliiHiis inventoried lot bald e.igles In the lllii 
 Natuial HiMnn Sui\<\. 1972-1987. 
 
 •'U.S. .Army Corps of Fngineers (1978). Illinois Division of W atcr- 
 
 wavs (I9(=i9). 
 ''H.igen et al. (1977). Haveia (1985). 
 
February 1 988 
 
 Havera and Kruse: Winter Populations of Bald Eagles 
 
 1986. However, the mean number of eagles seen per 
 inventory was the most logical method of presenting 
 the data. 
 
 Upper Mississippi River Region. The Upper Mis- 
 sissippi River Region extends from the Illinois- 
 Wisconsin border southward to approximately Rock 
 Island, Illinois (Fig. 6). This region was surveyed from 
 October through March during the three winters of 
 1980-1983 and substantial numbers of eagles were 
 counted. The floodplain in this area provided attract- 
 ive winter habitat for bald eagles (Fig. 7). 
 
 Fig 7 - 1 vpual iivcniie habitat of the L'ppcr Mississi] 
 gion. 
 
 The seasonal pattern of eagle use of the Upper 
 Mississippi River Region is shown in Figure 8. Annual 
 peak population counts occurred between 2 February 
 and 23 March. Substantial numbers of birds were still 
 present when counts were terminated each spring. 
 The greatest 1-day count was 213 eagles on 23 March 
 1983. Southern (1964) observed peak numbers of 268 
 and 225 eagles in this region on 2 February 1962 and 
 on 5 February 1963, respectively. A total of 2,663 
 eagle sightings was recorded in this region; 34.99? of 
 those were immatures. The proportion of immature 
 
 ISO ■ 
 140- 
 130 - 
 
 70 ■ 
 60 ■ 
 50- 
 
 iO ■ 
 
 IMMATURES 
 TOTAL 
 
 birds ranged from 30.9 to 4 1 .69c on individual census 
 flights. 
 
 The mean count per inventory on individual cen- 
 sus areas is shown in Figure 9. The area between the 
 Wapsipinicon River and Princeton was the most heav- 
 ily used in this region, with an average of 20.9 eagles 
 sighted per inventory (Appendix). Other heavily used 
 areas were the Bellevue to Green Island segment and 
 the Fulton to Albany area. The Upper Mississippi 
 River Region also includes the Oak Valley F.agle Ref- 
 uge in Rock Island Clounty. The heavy use of this area 
 by wintering bald eagles was documented by Klton 
 Fawks through 25 years of observation and because 
 of its importance, the refuge was purchased by the 
 Illinois Department of Conservation (IDOC) in 1980. 
 
 For the Upper Mississippi River Region as a whole, 
 bald eagles occurred at an average density of 1.38 
 eagles per river mile or 0.96 eagle per square mile of 
 wetland habitat from 1980-1983. These values are 
 higher than those for any other region of the Missis- 
 sippi and Illinois rivers; however, the Upper Missis- 
 sippi River Region has been flown for fewer years 
 than the other regions (Table 4, Fig. 6). 
 
 Upper Central Mississippi River Region. The Upper 
 Central Mississippi River Region stretches from ap- 
 proximately Rock Island, Illinois, to Keokuk, Iowa 
 (Fig. 6). Between 1972 and 1986, most areas within 
 this region were surveyed from 120 to 130 times. 
 Flights were made from September through De- 
 cember in 1972 to 1985, during Januarv from 1973 
 to 1986, and from February through .April from 1980 
 to 1985. 
 
 Lodi and Dam 16 
 
 15 29 12 26 
 
 lig. H.-Mcaii iiuinlur oi bald eagles (oiiiiliil |>< i 
 Ippcr Mississipi Rivir Region. HIHO-HW:! 
 
 Kig.O.-Mean luiinherof halrleagleMoiinteii pel invenloiv.iltensiis 
 areas KJlhiii ihe I'ppei Mississippi Rlvei Regiriii. Htmt-Ht.S:V 
 
Illinois Natural History Survey Biological Notes 
 
 No. 129 
 
 The level of eagle use in the Upper Central Missis- 
 sippi River Region from fall through spring is shown 
 in Figure 10. Few inventories were conducted during 
 late January and early February. In each year except 
 1983, at least one inventory was conducted in the fall 
 before any eagles were observed and those flights al- 
 lowed an approximation of the arrival date of bald 
 eagles in this region. Estimates of arrival dates of 
 eagles observed from the air for 1 1 autumns indicated 
 that arrival gradually became earlier. From 1972 to 
 1975 the first eagle sightings were in late November, 
 but from 1976 to 1981 the first observations usually 
 occurred in late October or early November. In 1982 
 and 1983 eagles were present in the Upper Central 
 Mississippi River Region by late September. Spring 
 data indicated that all eagles usually left this region 
 by early April. 
 
 Fig. 10. -Mean tuiiiiIki of b.ikl califs lounU'd per imciildi v in tlu- 
 tapper Ck-nlr.il Mississippi Ri\ir Region, l<l72-l'.l,Sli. 
 
 Peak, population counts occurred each year be- 
 tween 1 1 December and 7 March. The largest number 
 of eagles seen on a single day was 180 on 5 January 
 1984 and again on 2 December 1985. Immatine birds 
 ranged between and 48.3% of the eagles seen on 
 individual flights whereas the overall proportion of 
 immatures censused in this region was 34.7%. 
 
 Mean counts per inventory on individual areas are 
 shown in Figure 1 1. F.agles are found throughout this 
 region, but the areas between Ft. Madison. Iowa, and 
 Keokuk, Iowa, generally hosted the most birds (Fig. 
 1 1, Appendix). The average density of bald eagles in 
 the Upper Central Mississippi River Region was 0.46 
 bird per river mile or 0.36 per scjuare mile of wetland 
 habitat. 
 
 Lower Central Mississippi River Region. The Lower 
 Central Mississippi River Region extends from 
 Keokuk, Iowa, southward to Cirafton, Illinois, and in- 
 cludes the lower 26 miles ot the Illinois River (Fig. 6). 
 This region also was censused from 120 to 130 titnes 
 between 1972 and 1986. Census fiights were made 
 during September through December from 1972 to 
 
 LockandDamie 
 
 Muscatine 
 
 LockandDamI? 
 
 Ft. Madison 
 
 Keokuk 
 
 • <1.00 
 • 1.00-2.99 
 % 3.00-4.99 
 A 5.00-9.99 
 
 Fig. 11. -Mean number ol bald eagles tDunled per invciitorv al 
 tcn.sus area.s within the Lpper (Central Mississippi River Region. 
 1972-1986. 
 
 1985, during January from 1973 to 1986, and during 
 February through April from 1980 to 1985. 
 
 Seasonal trends in eagle numbers in the Lower 
 Central Mississippi River Region are shown in Figure 
 
 ^80^ 
 
 260 
 
 240 
 
 220 
 
 200 
 
 160- 
 
 3- IMMATURES 
 ■• - TOTAL 
 
 Ig. I'J. 
 
 ,o\ser ( 
 
 22 6 20 3 17 I 15 29 12 26 9 23 9 23 6 20 
 >T OCT NOV DEC JAN FEB MAR APR 
 
 DATE 
 
 Me.in luinibc'i nl b.ild e.igles loiniled pel in\enloi\ in the 
 enli.il Mississi|)pi River l<egion. l972-l9Sti. 
 
February 1988 
 
 Havera and Kruse: Winter Populations of Bald Eagles 
 
 13 
 
 12. Fall arrival and spring departure dates were simi- 
 lar to those observed in the Upper Central Mississippi 
 River Region. The progression to earlier arrival of 
 eagles observed on aerial inventories during fall in 
 recent years also occurred in this region. 
 
 The highest counts for each year occurred between 
 1 1 December and 8 March and the largest number 
 of bald eagles recorded in this region was 527 on 6 
 January 1986. Immature eagles accounted for to 
 66.7% of the birds seen on individual flights and an 
 overall average of 35.6% of the eagles sighted in this 
 region were immatures. 
 
 Figure 13 depicts the mean number of eagles per 
 inventory counted on individual areas. The largest 
 gatherings of bald eagles within this region occurred 
 at Flat and Swan lakes near the confluence of the 
 Illinois and Mississippi rivers (Fig. 14) and between 
 the towns of Keokuk and Meyer (Fig. 13) on the Mis- 
 sissippi River. The vicinity of Flat and Swan lakes 
 often held more eagles than any other census area in 
 this region (Appendix). Of 127 flights conducted at 
 Flat and Swan lakes, there were only 15 on which no 
 eagles were seen. The highest number of eagles 
 counted at Flat and Swan lakes was 269 (146 adults, 
 1 23 immatures) on 6 January 1 986, and this was 5 1 .0% 
 of the birds seen in the entire Lower Central Missis- 
 sippi River Region on that date. 
 
 The Keokuk vicinity (Fig. 15) hosts what may be 
 the largest concentration of wintering bald eagles 
 found anywhere on the entire Mississippi River. Large 
 
 numbers of eagles are attracted to the area near Lock 
 and Dam 19 at Keokuk in winter because of the open 
 water below the dam and the readily available supply 
 of fish killed or injured as they pass through turbines 
 of the hydroelectric plant associated with the dam. 
 The main item in the diet of bald eagles wintering in 
 Illinois is fish (Southern 1963, 1964, 1966, Jonen 
 1973, Fischer 1982, Harper 1983, Sabine & Klimstra 
 
 Fig. 1 4. -Southward view ol il 
 sissippi rivers, an iniporl.irii 
 
 .iilliuiu.i.rilH- Illinois and Mi' 
 Icii uiiiiciImj< l)al(l eagles. 
 
 1985). Each January, IDOC hosts the popular Bald 
 Eagle Appreciation Days in this area for the public to 
 view the large numbers of wintering eagles. In this 
 area, IDOC, The Nature Conservancy, and W'estern 
 Illinois University manage properties (Fig. 15) that 
 are maintained for foraging and night roosting of 
 bald eagles. The numbers of bald eagles in the Keokuk 
 area are undoubtedly higher than the INHS aerial 
 census data reflect because not all of the managed 
 properties are censused and because few flights are 
 made during January and February when bald eagle 
 numbers are usually at their zenith. 
 
 !,«. l:i. M. 
 
 < ensus area- 
 H»72-19K(i. 
 
 ,in iiunilx'i i>l h.iUI eagles iiMnilecl pel iruentiii\ M 
 wilhin llie lower ( enli.il Mississippi Rivei Regiciii. 
 
 1 ig l.'i. Nciiilusesiward view of llie Ceil.ii (ilen K 
 H-iiuixk (iiiiiiiiv. Illinois, and llie f1(M)d|)laiii l>cl<iw I 
 HI ai Keokuk, loua. litis area Ivpii.illv hosis die lai 
 III wiiileriiig bald eagles in the Mississippi Ki\er val 
 John Warniuk). 
 
 igle Koosi in 
 cK k and Dam 
 gesi iiumltcr 
 lev (I'hoio hv 
 
Ilinois Natural History Survey Biological Notes 
 
 No. 129 
 
 The average density of bald eagles in the Lower 
 Central Mississippi River Region for all inventories 
 was 0.48 per river mile or 0.34 per square mile of 
 wetlands. These values are similar to those for the 
 Upper Central Mississippi River Region. 
 
 Lower Mississippi River Region. The Lower Missis- 
 sippi River Region extends from approximately St. 
 Louis, Missouri, southward to Cairo, Illinois (Fig. 6). 
 Most areas in this region were inventoried between 
 105 and 110 times since 1972. Censuses were made 
 during October through April from 1972 to 1985 and 
 in January 1986. 
 
 The seasonal variation in eagle numbers in the 
 Lower Mississippi River Region is shown in Figure 
 16. The first eagle sightings in this region usually 
 
 8 22 e 20 3 17 I IS 29 12 26 9 23 9 23 6 20 
 SEPT OCT NOV DEC JAN FEB MAR APR 
 DATE 
 
 Fig. 16.-Mc'.tM iiiiiiibfr of bald eagles counted per inveiuoi y in ihe 
 Lower Mississippi River Region. 1972-l9<S(i. 
 
 occurred from late October to mid-November, some- 
 what later than in the more northern reaches of the 
 Mississippi River. Spring departures, however, were 
 usually similar in most years to those in other regions 
 of the Mississippi River, although from 1983 to 1985 
 eagles were present until late April, or 2 to 3 weeks 
 later than in other regions. 
 
 Peak population counts occurred between 4 Janu- 
 ary and 18 February in this region. The highest 
 number of bald eagles observed on one day was 262 
 on 6 February 1979. Immature birds ranged between 
 and 1009^ of the eagles seen on individual inven- 
 tories and averaged 33.6% for all inventories. 
 
 The mean number of eagles per inventory for 
 areas within this region is shown in Figuie 17. Num- 
 bers of bald eagles were higher in the downstream 
 portion of this reach (Appendix). Few eagles were 
 seen between St. Louis and Kimmswick, Missouri, but 
 numbers steadily increased to the area from Cajie 
 Girardeau, Missouri, to Cairo, Illinois, where the high- 
 est numbers were seen. This stretch of the river is 
 also adjacent to some of the major winter areas for 
 Canada geese (Branta canadensis) in southern Illinois. 
 
 The average density of bald eagles in the Lower 
 Mississippi River Region was 0.2 1 bird per ri\er mile 
 
 <1.00 
 1, 00-2,99 
 3,00-4,99 
 5,00-9,99 
 >10,00 
 
 Fig. 17.— Mean niniiljer ol bald eagles counted per inventory at 
 census areas within the Lower Mississippi River Region, 1972-1986. 
 
 or 0.20 per square mile of wetland habitat. These 
 density values of bald eagles were the lowest of all the 
 Mississippi Ri\er regions. 
 
 Upper Illinois River Region. The L^pper Illinois River 
 Region stretches from Morris, Illinois, to near Spring 
 Valley, Illinois (Fig. 6). Most portions of this region 
 were surveyed 59 times between September and .-Vpril 
 from 1976 to 1985. This relativelv short, highly de- 
 veloped segment of the Illinois River vallev seldom 
 showed substantial use bv bald eagles. 
 
 The seasonal pattern of eagle numbers in the 
 Upper Illinois Ri\er Region is shown in Figure 18. 
 The trend toward earlier observations of eagles in the 
 fall during the years inventoried was also apparent in 
 this legion. In the late 1970s, eagles were usually first 
 seen during aerial inventories in the latter half of 
 November, but in more recent years, the first observa- 
 tions generalh occurred in mid-October. The earliest 
 sighting ot bald eagles during any census in all regions 
 (F"ig. 6) occurred in the LIpper Illinois Ri\er Region 
 when four birds were seen between L'tica ami Mar- 
 seilles on 10 September 1980. Spring departure ot 
 eagles from the L'i)per Illinois Ri\er Region was gen- 
 erall\ completed b\ earK .\piil. 
 
February 1988 
 
 Havera and Kruse: Winter Populations of Bald Eagles 
 
 IS 
 
 I 15 29 12 
 DEC JAN 
 
 Fig. 1 8. -Mean numbci of bald eagles counted per invenloiv in ihe 
 Upper Illinois River Region. 197(5-198.5. 
 
 Seasonal patterns of hald eagle octiirrence in the 
 Central Illinois Rivei Region are ilhistiated in Figure 
 20. No census tliglits were toiuhuied from mid- 
 
 Peak population counts occurred between 3 Janu- 
 ary and 9 March in this region with the highest count 
 of 53 eagles reported on 20 January 1982. Generally, 
 fewer than 25 eagles were seen on each census in this 
 region. Immature birds consisted of to 50.0% of the 
 eagles observed on individual inventories, and the av- 
 erage proportion of immatures for all eagles seen was 
 31.8%. 
 
 The mean number of bald eagles observed per 
 inventory for individual areas is depicted in Figure 
 19. The downstream portion of this region, between 
 La Salle, Illinois, and Spring Valley, Illinois, was gen- 
 erally used the most by eagles (Appendix). The density 
 of bald eagles in the Upper Illinois River Region av- 
 eraged 0.20 per river mile or 0.47 per square mile of 
 wetlands. 
 
 Fig. 19. -Mean nnnilxi ol bald eagles (ounled [)er inventory at 
 census areas within the L pper Illinois River Region. 1976-198.5. 
 
 Central Illinois River lief^on. The Central Illinois 
 River Region consists |)rimarily of the Peoria Naviga- 
 tion Pool and extends from near .Spring Valley to 
 Lower Peoria Lake (Fig. 6). This region was inven- 
 toried approximately 125 times between 1972 aii<l 
 1986. Flights were made during Si-|)iembfi ihroiigh 
 December from 1972 to 1985, during |anuarv from 
 1973 to I98(), and during February thiough April 
 from 1980 to 1985. 
 
 Fig. 'id. -Mean number ol b.il<l c.igles (ounled pel iiiventor\ in the 
 CeiUral Illinois Ri\ei Region, I972-198(). 
 
 January to late February. The trend towards earlier 
 observations dining aerial inventories of eagles in the 
 fall was also apparent in this region. Since 1981. birds 
 were generally present bv late SejiteiTiber. As in many 
 other parts of Illinois, all eagles li.id depai ted b\ earlv 
 April. 
 
 P'agle jjoptiialioiis in this tegion ])eake{l between 
 2 I)e(ciiil)ei and 21 .Man it. llie laigesi number seen 
 on one inventoi \ was 1 70 on 1 9 Marc h 1 980. but since 
 then the highest number of eagles seen on a single 
 day was 104. The i)roporti()n of immatures ranged 
 from to 54.8% of all eagles seen on individual counts 
 and the overall mean for inmiatmes was 33.1*^'? for 
 all censuses. 
 
 Ilie mean number of eagles (otmled pel iinenloi \ 
 for individual areas is shown in Figine 21. Some of 
 the areas in this region with high use 1)\ bald eagles 
 included Ililduoik Slough (Maisball Counl\). Rite 
 Pond at loss from ('.liillitollie. l'|)pei Peoria Lake, and 
 Cioose and Senaihwine lakes (Fig. 22) in Bureau and 
 Putnam counties (.Aijpendix). llie densiis of bald 
 eagles observed in the Central Illinois River Region 
 averaged 0.07 eagle per i ivt-i mile or (1. 17 per s(|uare 
 mile of wellantl habit. ti. 
 
 Lower Illinois liii'er Region. 1 he I.owei Illinois River 
 Region consists priniarilv t>f the La (iiange Pool of 
 (he Illinois River and stretches lioin Pekin to Naples 
 (Fig. <>). I his region has been more t loselv monitored 
 for eagles than anv other with over 1.30 inventories 
 l.iken liom 1972 to 1980. (^c'lisus lliglils \kv\v made 
 fluiing Seplembei lliiough Deteiiibei from 1972 to 
 1985. during |.iiiuai V lioiii 197!^ I o 198(1. .tnd tlui ing 
 Februarv through .\piil from 1980 to 19M5. 
 
 Seasonal variation in eagle use ol this region is 
 sliiivMi in Figure 23. No i ensus flights were tonclui led 
 I loin mid- 1. Ill t I.I I V to l.ilc Icbi ti.iiv . I imesof f.illai i iv- 
 
linois Natural History Survey Biological Notes 
 
 No. 129 
 
 <1.00 
 1.00-2.99 
 
 I 3.00-4.99 
 ) 5.00-9.99 
 
 Fig. 21. -Mean number of bald eagles tountecl per inventory at 
 cen.sus areas within the Central Illinois River Region, 1972-1986. 
 
 Fig. 23. -Mean number of bald eagles counted per 
 Lower Illinois River Region. 1972-1986. 
 
 to 50.09^ of tlie total eagles observed, and the overall 
 proportion of immatiires was 34.79^ for all inven- 
 tories. 
 
 The mean number of eagles inventoried per cen- 
 sus flight is illustrated in Figure 24. ,\reas with the 
 most use by bald eagles intluded Chautauqua National 
 Wildlife Refuge (Fig. 25), Crane Lake, Clear Lake, 
 Cuba Island, and Jack Lake (Appendix). .\11 of these 
 areas are privately owned except the 4,500-acre 
 (1,822-ha) Chautauqua Refuge. 
 
 al in late September and early October and spring 
 dejiaiture by eailv \pv\\ were similar to those in the 
 Cential Illinois Ri\er Region. Eagles arri\ed in the 
 Lowei Illinois Ri\er Region approximately 1 week 
 earlier than in the Cential Illinois River Region in 2 
 of the 15 years inventoried. 
 
 Peak population counts have occurred from 2 De- 
 cember until 18 March; the latter is also the date of 
 the highest 1-day count of .345. The proportion of 
 immatures seen on indixidual censuses ranged from 
 
 Fig. 24. -Mean number ol b.iUl eagles i 
 census are, IS uilliiii llie Lower Illinois Ri' 
 
 • 100-299 
 % 3.00-4-99 
 
 innied per in\enior\ a 
 er Region. 1972-1986. 
 
 Fig. 22.-Fastern sh, 
 into Senacliw'ine L.tk 
 
 The estimated density of bald eagles in the Lower 
 Illinois River Region averaged ().5(i per river mile or 
 0.49 per squaie mile of wetland habitat. The average 
 density per scjuare mile of wetlands (0.49) in this re- 
 gion was slighth higher than the value lor the ('entral 
 and L'pj)ei Illinois River regions (0.47) and was also 
 highei tlian the values for all of the Mississippi River 
 
February 1988 
 
 Havera and Kruse: Winter Populations of Bald Eagles 
 
 Fig. 25.-Northcast\vai(l \icw ol the Chautauqua Lake area, an 
 important winter site for bald eagle.s in the Lower Illinois River 
 Re>;ion. 
 
 regions (0.20-0.36), with the exception of the Upper 
 Mississippi River Region (0.96). The average density 
 of eagles per river mile (0.56) in the Lower Illinois 
 River Region was slightly lower than the value for the 
 Central Illinois River Region (0.67), higher than those 
 values for the Upper Illinois (0.20), Lower Mississippi 
 (0.24), and the Upper and Lower Central Mississippi 
 regions (0.46 and 0.48, respectively), but substantially 
 lower than the value (1.38) for the Upper Mississippi 
 River Region. 
 
 Central and Southern Lakes Region. A vast majority 
 of bald eagles wintering in Illinois was found in the 
 floodplains of the Illinois and Mississippi rivers (Figs. 
 6 and 26). Relatively small numbers of eagles were 
 counted in other regions. Of the nine reservoirs and 
 cooling lakes censused in central and southern Illinois 
 (Fig. 6, Appendix), five (Sangchris, Carlyle, Rend, 
 Baldwin, and Springfield) were inventoried on a reg- 
 ular basis from October through April since 1972. 
 However, only Carlyle and Rend lakes averaged more 
 than one eagle per census (Fig. 26, Appendix). No 
 eagles were sighted at Clinton Lake. Kagje use of these 
 lakes in central and southern Illinois declined in recent 
 years. 
 
 Northeast Lakes Region. The natural lakes, reser- 
 voirs, and cooling lakes in counties of northeastern 
 Illinois (Fig. 6, Appendix) alsf) hosted few eagles. 
 These lakes were censused from September through 
 April since 1976. Lhe M( Henry Dam area in Mc Henry 
 County was the only area that held an average of tnore 
 than one eagle per census (Pig. 26, Appendix). Kaglc 
 numbers were slighilv higher in the late 1970s in this 
 region, but fell to near zero iti later years. 
 
 Surffiir-wnirrI Litkc^ Rtgiini. Inveiitoi ies ol surface- 
 mined lakes in Fulton and Knox (onniies in west- 
 central Illinois (Fig. 6) reveali-d limited use bv bald 
 eagles (Fig. 26). Inventories were conducted from Oc- 
 tober tbiough Match frotn 1980 to I98.T. No eagles 
 were sighted r)n most of the lakes in this r<-gion bul 
 
 small numfjers were seen on a regular basis on the 
 Central Illinois Light Company (CILCO) property 
 (Appendix). 
 
 Lower Kaskaskia River Region. The Lower Kaskaskia 
 River Region (Fig. 6) included the lower 30 miles of 
 the river from approximately Fayetleville to Chester 
 on the Mississippi. This region was surveyed during 
 October to April from 1982 to 1986 (Fig. 26). From 
 1982 to 1985 bald eagle use in this region was low 
 with never more than one eagle sighted on a census; 
 however, on 7 January 1986, nine eagles were ob- 
 served (Appendix). 
 
 Other Inventories. Other studies that monitored 
 bald eagle populations over one or two winters in 
 small geographic areas have been conducted in Il- 
 linois. Such studies, because of the frequency of counts 
 and the limited area involved, provided information 
 on the abundance and use patterns of bald eagles that 
 is not obtainable from periodic regional counts. 
 
 Southern (1963) monitored eagle populations near 
 the Savanna Army Depot in Jo Daviess County in the 
 
 * 
 
 •lOO 
 
 • 
 
 1 00 2 99 
 
 • 
 
 3 00 4 99 
 
 • 
 
 5 00 9 99 
 
 • 
 
 •10M 
 
 liK 'Jli.~M<'.in niiinlH'i nl h.ilil ('.i|{k'> xiunlcd (mt invrnl(ii\ al 
 (ensiis areas within all i enrolls. 1972-UINf). 
 
Illinois Natural History Survey Biological Notes 
 
 Upper Mississippi River Region (Figs. 8 and 9) during 
 the winterof 1961-1962. He reported that eagles were 
 present in that area from before 9 December until 
 1 April. The peak population count occurred in this 
 area on 2 February when 262 birds were counted 
 along a 14-mile census route. 
 
 A second study by Southern (1964) was done in 
 the same area during the winter of 1 962-1 963. Counts 
 were initiated earlier in the fall and the first eagles 
 were sighted on 2 1 October. After a peak of 225 birds 
 on 5 February, all eagles had left the area by 9 April. 
 Through most of the winter, only about 10 to 12% 
 of the bald eagle population in this area were imma- 
 ture birds. 
 
 Jonen (1973) studied bald eagles on a 6-mile reach 
 of the Mississippi River extending downstream from 
 Lock and Dam 19 at Keokuk (Figs. 12 and 13). In the 
 winter of 1970-1971 he first noticed an immature 
 bald eagle in this area on 3 October. The first adult 
 eagle was sighted on 13 December and the peak popu- 
 lation count for that winter was 49 (40 adults, 9 imma- 
 tures) on 8 January. Jonen sighted the first eagle, an 
 immature, during the 1971—1972 season on 18 Oc- 
 tober. An adult eagle was first sighted on 29 
 November, and the largest niunber of eagles sighted 
 was 66 (57 adults, 9 immatures) on 12 February. 
 
 Two patterns noticed by Jonen (1973) were that 
 immature eagles were present in the area earlier in 
 the fall and later in the spring than adults and that 
 the number of eagles present in his study area in- 
 creased during periods of extremely cold weather. 
 
 Fischer (1982) studied the same area described by 
 Jonen (1973) and found that bald eagle use of this 
 area had increased dramatically in the 7 years since 
 Jonen's work. During the winter of 1978-1979, which 
 was a winter of record-breaking low temperatures and 
 heavy snowfall, Fischer (1982) monitored eagle num- 
 bers from early December to early April. A peak count 
 of 454 eagles (359 adults, 88 immatures, 7 not aged) 
 occurred on 18 January 1979. The count far exceeded 
 any recorded previously in the vicinity of Lock and 
 Dam 1 9 and was not equaled in the following 6 years. 
 
 Fischer (1982) also made inventories from late 
 November 1979 until the end of March 1980. During 
 a relatively mild winter, the peak number of eagles 
 counted was 120 (89 adults, 31 iinmatures) on 18 Feb- 
 ruary 1980. The peak for 1979-1980 was only 26.4% 
 of the peak count for the previous winter. 
 
 Harper (1983) studied eagle populations in the 
 vicinity of Lock and Dam 24 at Clarksville, Missouri, 
 in the Lower Central Mississippi River Region (Figs. 
 6 and 13). He conducted aerial and ground sinveys 
 in 1980—1981 and ground counts in both foraging 
 and night roosts during the winterof 1981-1982. Aer- 
 ial counts conducted in 1980-1981 gave consistently 
 lower counts than ground counts done simulta- 
 neously. Daytime ground counts usually provided 
 lower totals than counts done on the same dale at 
 night roosts. I he highest count recorded during this 
 
 study was 168 eagles (92 adults, 57 immatures, 19 
 unaged) observed at a night roost on 26 January 1982. 
 
 Sabine and Klimstra ( 1 985) inventoried bald eagles 
 in southern Illinois at Union County and Horseshoe 
 Lake Conservation areas during 1979-1981 and at 
 Crab Orchard National Wildlife Refuge (CONVVR) 
 during 1980—1981. Eagles are probably attracted to 
 these areas by the large numbers of wintering Canada 
 geese because crippled and dead geese provide a read- 
 ily available source of food for wintering eagles. Eagles 
 arrived in these areas in late October and departed 
 by early March. Peak population counts for eagles in 
 1979—1980 were 71 at Union County on 19 February 
 and 78 at Horseshoe Lake on 8 February. During 
 1980-1981, peak populations of eagles occurred on 
 23 January when there were 79 at Union County and 
 77 at Horseshoe Lake. Approximately 76% and 65% 
 of the peak populations of eagles were immatures at 
 Union County and Horseshoe Lake, respectively. 
 These values for immatures are much higher than 
 those noted for areas along the Illinois and Mississippi 
 rivers (Jonen 1973, Fischer 1982, Havera et al. 1984). 
 CONWR was used by relatively few eagles as shown 
 by a peak count of only 29 in mid-December 1980. 
 
 Southern et al. (1985) conducted 12 statewide aer- 
 ial surveys of bald eagles during the winter of 1984— 
 1985. This was the first attempt at 1-day statewide 
 censuses. All previous studies included 1-day counts 
 in relatively small areas (Jonen 1973, Sabine 1981) or 
 counts over large areas that were completed in a 
 period of days (I NHS aerial surveys). 
 
 In addition to documenting changes in bald eagle 
 populations in Illinois, which peaked at 989 on 8 Feb- 
 ruary 1985, Southern et al. (1985) identified 13 essen- 
 tial areas of winter habitat using criteria suggested by 
 Crier et al. (1983). These included any area of 15 mi 
 (24 km ) or less in length along a river that was used 
 by 15 or more bald eagles for 2 weeks or longer. 
 Southern et al. (1985) found that the most heavily 
 used winter area was that portion of the Mississippi 
 River near Lock and Dam 19 at Keokuk. In the Illinois 
 River valley, the area used most by bald eagles was 
 Pere Marquette State Pai k in Jersey County. .Ml areas 
 found to be essential winter habitat by Southern et al. 
 (1985) are shown in Figure 27. 
 
 Small concentrations of bald eagles sometimes 
 occur away from the floodplains of major rivers. For 
 example, between 20 and 25 bald eagles were seen 
 frequenting a wooded area of Pike Countv during the 
 1986-1987 winter. These eagles were feeding on live- 
 stock carcasses and were roosting close to the food 
 source and not in the Illinois or Mississippi river 
 fioodplains. 
 
 DISCUSSION OF CENSUS DATA 
 
 Although a concentrated effort has been made to 
 monitor the numbers of bald eagles wintering in II- 
 
February 1988 
 
 Havera and Kruse: Winter Populations of Bald Eagles 
 
 19 
 
 Clarksvllle (12) 
 
 Horseshoe Lake (1 0) \© 
 
 Fig. 27.-I.<)cali<)iis of essential bald eagle wiiilei li.iliiMi Kliriiilied 
 by Southcin cl al. 1985. Numbers inditale iin|joilaiin- rankiiiH- 
 
 linois, bald eagle census data for Illinois should be 
 considered anestimateor index of actual pojjulalions. 
 
 For a variety of identified and imdeteriTiined 
 reasons, counts of bald eagles made on a specific area 
 are subject to extreme short-term variations. This vari- 
 ation is well demonstrated by data from Fischer 
 (1982). In his study, two or three ground counts often 
 were made on the same day, and those counts differed 
 by as much as 35% or 150 eagles. However, variations 
 in the numbers of eagles seen were not consistent. 
 Numbers of eagles sometimes increased or decreased 
 during the same day. I'he lack of sinuiltaneous counts 
 over a wide area and the mobility of bald eagles make 
 it diffic ult tf) determine whether daily flue luations in 
 numbers were c aiised by lo( al movements or bv shifts 
 in populations over larger geograjjhic aieas. 
 
 Dunstan and Fawks (19HI) stated that food avail- 
 ability is the primary reason (or the southwaid move- 
 ment of bald eagles into Illinois during wintei. Keister 
 et al. (1987) reported that the interaction of food avail- 
 ability and proximity of loosting habilal appealed to 
 
 be a primary factor in the behavior of wintering bald 
 eagles. Structures such as locks and dams or activities 
 that maintain open water in winter and, therefore, 
 the availability of fish serve as an attractant to bald 
 eagles, partic ularly if suitable daytime perches and 
 night roost areas are nearby. As noted by Steenhof 
 (1978), the abundance and distribution of wintering 
 bald eagles have been greatly af fee ted by construe tion 
 of dams and impoundments. Fischer (1982) found 
 that the extent of ice cover on the Mississippi River 
 influenced the local distribution of eagles. As the area 
 of open water changed, the eagles shifted their pat- 
 terns of use to take advantage of available forage. 
 Harper (1983) reported similar shifts in bald eagle 
 use patterns near IakV. and Dam 24. 
 
 Jonen (1973) and Fischer (1982) reported a corre- 
 lation between extremely cold temperatures and in- 
 creasing numbers of bald eagles present on the Lock 
 and Dam 19 study area. An increase in eagle numbers 
 generally occurred a few days after the onset of a cold 
 period. However, there was no apparent relationshi]) 
 between population changes of eagles and low temper- 
 atures over the large geographic areas sinveyed aer- 
 ially by I NHS, a finding which suggests that the re- 
 lationship between movement and temperature noted 
 by Jonen (1973) and Fischer (1982) could be a local 
 phenomenon. Millsap (1986) found that bald eagles 
 appeared to winter farther south during unusually 
 cold winters. 
 
 Southern (1963, 1964) and others suggested that 
 immature bald eagles move south earlier and move 
 farther south than adults. Millsap (1986) found that 
 the percentage of immatine bald eagles in the mid- 
 winter survey increased at southern latitudes. Both 
 jonen (1973) and Fischer (1982) reported sighting a 
 higher proportion of innnatutes early in the winter 
 than during midwinter. Fischer (1982) also noted an 
 increase in the proportion of innnatures as spring 
 approached. The largest proportions of immatures 
 reported in Illinois were at wildlife areas in southern 
 Illinois (Sabine & Klimstra 1985). These observations 
 support the concept that immature bald eagles move 
 soiuhward earliei and farther than adults. IXHS cen- 
 sus data collected over lelalively large areas did not 
 reveal such patterns of movements by immature bald 
 eagles. 
 
 The accuracy of various methods of counting 
 eagles has been debated. Southern (19(")4) reported 
 that simultaneous ground and aerial counts gave simi- 
 lar results; he suggested that aerial counts validated 
 the accuracy of ground counts. Harper (198.3) found 
 that aerial surveys gave consistently lower counts th.in 
 ground coinits in the same area. Havera et al. (1984) 
 csiimaicd ihai 75 to 90'^ of the eagles present were 
 counted during aerial survevs. 
 
 Density of vegc-talion could easily affect the accii- 
 lacy of observeis when counting eagles from the 
 ground or the air. Kven inider good conditions, imma- 
 ture bald eagles can be difficult to locate because of 
 their moiilccl daik |)luTiiagc-. However, weather mav 
 
Illinois Natural History Survey Biological Notes 
 
 have the greatest influence on the accuracy of bald 
 eagle counts. Fog, rain, snow, and wind not only make 
 it difficult for observers to see and age eagles but such 
 conditions also may influence the activity of eagles, 
 thereby making them less visible. 
 
 Difficulties in obtaining accurate determinations 
 of eagle numbers in Illinois do not eliminate the value 
 of such counts. The counts can identify important 
 winter areas and document trends in bald eagle popu- 
 lations. The bald eagle inventories organized by Elton 
 Fawks, for example, were prompted by concern over 
 the low proportion of immatures seen in winter popu- 
 lations during the 1950s (Fawks 1983). After quickly 
 increasing from 12.3% in 1961 to 27.6% in 1965, the 
 proportion of immatures sighted on Fawks' counts 
 has fluctuated slightly around a value of 30%. As with 
 any migratory species, suitable winter habitat is essen- 
 tial to the survival of individuals and the subsequent 
 reproductive success of the population. 
 
 NIGHT ROOSTS 
 
 Night roosts generally offered seclusion from 
 human disturbance and protection from cold winds. 
 At many of the roost sites, a windbreak was provided 
 by the walls of a ravine or glen. On level areas, eagles 
 selected trees for roosting that were protected by other 
 trees (Fig. 28) (Fischer & Osterfeld 1981, Sabine & 
 Klimstra 1985). Cotton woods (Populus deltoides) were 
 the preferred roost tree in some areas, and it appeared 
 that size and configuration of available trees were im- 
 portant. Bald eagles generally selected trees that were 
 taller than surrounding ones and had large, horizontal 
 branches (Sabine & Klimstra 1985). 
 
 Although bald eagles perch and forage along 
 major stretches of the Illinois and Mississippi rivers, 
 relatively few areas have been identified and reported 
 as night roosts (Fig. 29). Other undiscovered or unre- 
 ported night roosts undoubtedly exist along the Il- 
 linois and Mississippi rivers. Dunstan and Fawks 
 (1981) identified and described six night roosts as fol- 
 lows: 
 
 1) The Savanna Army Depot and nearby islands 
 include about 13,000 acres (5,260 ha) in Jo Daviess 
 and Carroll counties. Four specific night roost sites 
 have been identified on the area. There are also recent 
 records of nesting attempts on Depot property. 
 
 2) The Oak Valley Eagle Refuge in Rock Island 
 County is owned and managed by the NWF and 
 IDOC. There are four wooded ravines on the refuge 
 that were used by roosting eagles. 
 
 3) Cedar Glen Eagle Roost (Fig. 15) is located in 
 Hancock County between Hamilton and Warsaw. The 
 roost and surrounding eagle foraging areas have been 
 purchased and protected by a cooperative effort of 
 the Illinois Chapter of The Nature Conservancy, 
 IDOC, and Western Illinois University. 
 
 4) Pere Marquette State Park is located near the 
 confluence of the Illinois and Mississippi rivers in jer- 
 sey County. The area around the park provides forag- 
 
 Kig. 28.— Crystal fllen Eagle Roost in Hancock ("oiintv near Lock 
 and Dam 19 on the Mississippi River. The sycamore {Plaluniis oc- 
 inlniliilis) in the foreground was used by as many as 20 eagles 
 nightly during January and February, 1979 (David L. Fischer, per- 
 sonal communication 1986). Houses built nearby during the sum- 
 mer of 1979 discouraged subsequent eagle use of this glen as a 
 night roost (Photo by David L. Fischer). 
 
 ing and resting habitat, but most night roosting occur- 
 red in three hollows within the park. 
 
 5) Clarksville Island is located in the Mississippi 
 River along Calhoun County. The island, owned bv 
 The Nature Conservancy, was used by eagles through- 
 out the winter. 
 
 6) Burlington, Craigel, and Otter islands are lo- 
 cated in the Mississippi River along Henderson 
 County and each has a night roost. A variety of habitats 
 appropriate for daytime use by bald eagles is available 
 in the area. 
 
 Very few night roost areas along the Illinois River 
 have been identified, mainly because of a lack of re- 
 search. Robert Phelps, John Grigsby, and James 
 Waycuilis (personal communications 1986) reported 
 roosts in Putnam County near the Illinois River, at 
 Rice Lake in Fulton County, and at Marshall County 
 Conservation Area, respectively (Fig. 29). Additional 
 night roosts likely occur in the vicinity of foraging 
 areas such as Goose and Senachwine lakes. Peoria 
 Lake, Chautauqua National Wildlife Refuge, and San- 
 ganois Conservation Area. Roost areas were also iden- 
 tified at Union County and Horseshoe Lake Conser- 
 vation areas and at CONWR (Sabine & Klimstra 1985) 
 (Fig. 29). 
 
 RECENT BALD EAGLE NESTING 
 
 Bald eagles have constructed seseral nests in Il- 
 linois since 1973, and at least 16 eaglets fledged from 
 these nests from 1978 to 1987 (Fable 6). The first 
 rc( cut bald eagle nest in Illinois was built at COXWR 
 in 1973. Eagles were seen at this nest again in 1974. 
 Inil no eggs were laid in either of these \ears. .\ new 
 nest was built at COXWR in 1979. One eaglet fledged 
 fioin this nest in 1980 and two in 19S1. In 19S2. a 
 second nest was constructed at COXWR. One nest 
 
February 1 988 
 
 Havera and Kruse: Winter Populations of Bald Eagles 
 
 21 
 
 Horseshoe Lake 
 
 Fig. 29. -Locations ol bald eagle iiiglil rooMs idciuilicd bv Diiiislaii 
 ami Kauksd 981). .Sabine and Klinistia (I9,S.')). Robeil l'liel|)s (per- 
 sonal ( omnHMiicalion 19H(i). |obn (Irigsln (personal (onniuMMca- 
 lion I'.I.SI'o. and |.inies W.ixcuilis (pcisonal i oMUniinic .ilion I'.ISli). 
 
 was cl(.sti()\i(l l)\ liij^li winds, but the oiIr'i |)1(>(1iih-(1 
 two youn^ in 19X2, two in 1983, and one in 1981. 
 This second nest was blown to the ground in 198') 
 and ncj young were produced. Two nests were (on- 
 strueled at CX)\VVR in the spring of 1987. Two young 
 Hedged Iroin one nest, and one young fledged from 
 liieoilui . 1 wo neslsweie also (oiisi I uded a! CONW'R 
 in llie spring of 1987. Two voung fledged from one 
 nesi and one young was killed in a sloini jusl before 
 fledging fiom the oilier nesi. 
 
 Allliougli (X)\\VR has lediilh been ihc inosi |)i(>- 
 (hulive eagle nesliiig area in Illinois, the liisi sniiess- 
 ful !iest was at Horseshoe Lake in Alexander Coiuii). 
 Two yoiuig were produced from a single nesi ai 
 Horseshoe Lake in 1978. NosubsecjuenI nesting a(li\ ■ 
 ity was obseivt-d in that area until 1987 wlien a new 
 nest was constructed but no Noung wcic flc'dged. 
 
 Nesting activity has l)een seen at the Savanna Army 
 Depot each yeai since 1978. A nest was constructed 
 in 1978, enlaiged in 1979, blown down in 1980, and 
 replaced by a new nest in 1981. Kggs were laid and 
 incubated in 1982, but it is not known if the eggs 
 hatched. The nest was again destroyed by wind in 
 198;^ and rebuilt in 1984. The first successful use of 
 this nest was in 1985 when one eaglet fledged. 
 
 Othei bald eagle nest construction has been seen 
 at Union (louiity C.onsei vation Area in 1974 and 1980 
 and at Rend Lake in 1982 and 1983, but no young 
 were pioduced from these nests. 
 
 Although bald eagles are occasionalh' seen during 
 the late spring and summer months in the Illinois 
 River valley, the first documented nesting of bald 
 eagles in central Illinois occurred in 198(5. A nest was 
 established neai' the Illinois River in Pike County but 
 was later abandoned. In 1987 a nest was built in Han- 
 cock County; however, it was also abandoned. 
 
 Table 6.— Bald eagle nesting activity in Illinois, 1973-1987. 
 
 Year 
 
 Number of Nests 
 
 Number of Young Fledged 
 
 1973 
 1974 
 1975 
 1976 
 1977 
 1978 
 1979 
 1980 
 I98I 
 1982 
 1983 
 1984 
 1985 
 1986 
 1987 
 
 BALD EAGLE MORTALITY 
 
 .\ total of 'M) bald eagles found dead in Illinois 
 from 19()3to 1984 were submitted to federal laborato- 
 ries for determination of cause of death. Lhese birds 
 died from a variety of causes, many of which are re- 
 lated to human activity (Table 7, NWHI. 1985). 
 
 Like the nationwide data |)iesented earlier, these 
 moitalilv figures should be used as an index lalhei 
 than as an accurate measure of the causes of eagle 
 deaths in a po|)ulation because it is clilTiciilt to collect 
 a i.indom sample-. Shooting was the most common 
 cause of de.ith of l)ald eagles in Illinois, accounting 
 for 1 1 (.SO.O'r) of the deaihs (Table 7). At least two 
 moic- eagles weie shot to death in 1985. 
 
 .Six ac c iciental deaths of Ijald eagles resulted from 
 traumatic injuries, such as collisions with wires or ve- 
 hicles (Table 7). Other causes of eagle deaths, such as 
 electrcK ulion. emac iaiion, and trapping, were of rela- 
 tively minor importance in Illinois. 
 
 .Six eagles also died from poisoning during this 
 22-year period in Illinois, and foiu of those six birds 
 
linois Natural History Survey Biological Notes 
 
 Table 7.— Bald eagle mortality in Illinois, 1963-1984 (National 
 Wildlife Health Laboratory 1985). 
 
 
 Numberof 
 
 Percent 
 
 Cause of Death 
 
 Mortalities 
 
 ofTotal 
 
 Gunshot 
 
 11 
 
 30.6 
 
 Trauma (excluding gunshot, 
 
 
 
 electrocution, and trapping) 
 
 6 
 
 16.7 
 
 Poisoning 
 
 6 
 
 16.7 
 
 Lead 
 
 4 
 
 11.1 
 
 Other 
 
 2 
 
 5.6 
 
 Electrocution 
 
 3 
 
 8.2 
 
 Emaciation 
 
 1 
 
 2.8 
 
 Trapping 
 
 1 
 
 2.8 
 
 Other . ^ Decomposed, '' Open ' 
 
 8 
 
 22.2 
 
 "Death attributed to some cause other than those listed. 
 ''Carcass too badly decomposed for diagnosis. 
 ' No apparent cause of death could be determined from necropsy 
 examination and ancillary laboratory analyses. 
 
 were victims of secondary lead poisoning (Table 7). 
 Waterfowl, especially crippled and dead birds, are a 
 primary food item for bald eagles in some areas. Sev- 
 eral species of waterfowl have been identified as food 
 items for bald eagles in Illinois (Jonen 1973, Fischer 
 1982, Harper 1983, Sabine & Klimstra 1985). Feeding 
 on waterfowl carcasses was usually accomplished by 
 tearing the duck or goose apart with the beak while 
 standing on the carcass (Fig. 30) (Sabine & Klimstra 
 1985). 
 
 The growing problem of secondary lead poisoning 
 in eagles resulted in the requirement that nontoxic 
 (steel) shot be used for waterfowl hunting in 10 Illinois 
 counties in 1985. The prohibition of lead shot was 
 expanded to 22 counties for the 1 986 waterfowl season 
 (U.S. Dept. of Interior 1986). IDOC modified the non- 
 toxic shot zones for the 1986 waterfowl season to in- 
 
 clude primarily those areas that are used extensively 
 by waterfowl and bald eagles (W. Anderson, personal 
 communication 1986). This modification resulted in 
 the prohibition of the use of lead shot for sport hunt- 
 ing of waterfowl in corridors along the Illinois and 
 Mississippi rivers and in five entire counties, and in 
 part of the Rend Lake area (Fig. 31). This corridor 
 approach is supported by the findings of Havera and 
 Kruse (1986) in their evaluation of the distribution of 
 wintering bald eagles and waterfowl harvest in Illinois. 
 Restrictions on the use of lead shot for waterfowl hunt- 
 ing in Illinois are part of a growing nationwide effort 
 to reduce the availability of lead to eagles by reducing 
 the number of dead and crippled waterfowl with lead 
 shot embedded in their flesh or present in their diges- 
 tive systems. The USFWS is moving towards a total 
 nationwide ban on the use of lead shot for the hunting 
 of waterfowl by the 1991—1992 hunting season 
 (USFWS 1986). 
 
 SUMMARY 
 
 Continental numbers of bald eagles have increased 
 since eagles achieved legal protection and since the 
 prohibition of certain pesticides that affected repro- 
 ductive success of eagles. Wintering bald eagles are 
 attracted to Illinois by the availability of food, primar- 
 ily fish. Wintering eagles generally appeared in earlv 
 to mid-October in the northern and central regions 
 of Illinois and during late October in the southern 
 regions. Eagles usually had departed Illinois by mid- 
 April. Numbers of wintering bald eagles sighted in 
 Illinois during the midwinter inventory have in- 
 creased since its inception in 1957, and the highest 
 number censused by INHS was 1,217 on 6— 7 January 
 
 Fig. 30.-Iiiiiii.iiurc h.iM c.igle 
 I IcvdiMH (in .1 <1<.M(1 Canada ijooso 
 1 (I'hdioln linioilu Sniallcv.Min- 
 ' ncsoi.L Dcp.irlincnt ol Nalnr.il 
 
 Rcsoums ). 
 
February 1988 
 
 Havera and Kruse: Winter Populations of Bald Eagles 
 
 23 
 
 1986. The proportion of immature eagles counted by 
 INHS during the midwinter inventory typically 
 ranged between 30 and 37%. 
 
 The Illinois and Mississippi river floodplains and 
 the Canada goose refuges in southern Illinois hosted 
 a majority of bald eagles wintering in the state. The 
 mean number of eagles seen per inventory was highest 
 for the Upper Mississippi River Region with values 
 ranging from 4. 1 to 20.9 eagles per flight at the various 
 areas censused. Six of the 1 1 areas censused in the 
 Upper Mississippi River Region had an average of 
 more than 10 bald eagles per inventory. By compari- 
 son, only four areas in the 10 other regions censused 
 throughout Illinois, (the Keokuk- Meyer, Grand 
 Tower— Cape Girardeau, and Cape Girardeau— Cairo 
 stretches of the Mississippi River and the Flat and 
 Swan lakes area near the confluence of the Illinois 
 and Mississippi rivers) had values exceeding 10.0 for 
 the mean number of eagles per inventory. The Upper 
 
 Mississippi River Region was censused for just 3 years 
 (1980-1983). and only the Kaskaskia River Region 
 had fewer inventories. 
 
 Values for the estimated density of bald eagles per 
 river mile and per square mile of wetlands, respec- 
 tively, for the inventory regions of the Mississippi and 
 Illinois rivers were Upper Mississippi, 1.38 and 0.96; 
 Upper Central Mississippi, 0.46 and 0.36; Lower Cen- 
 tral Mississippi, 0.48 and 0.34; Lower Mississippi, 0.24 
 and 0.20; Upper Illinois, 0.20 and 0.47; Central Il- 
 linois, 0.67 and 0.47; and Lower Illinois, 0.56 and 
 0.49. Fewer bald eagles were observed in the Surface- 
 mined Lakes Region in west-central Illinois, the 
 Northeast Lakes Region, the Central and Southern 
 Lakes Region, and the Lower Kaskaskia River Region. 
 
 Intensified enforcement of laws protecting bald 
 eagles, the protection and management of habitats 
 identified as feeding, roosting, and major eagle use 
 areas, and the reduction of the availability of lead shot 
 to eagles should result in an increase in the number 
 of bald eagles that winter in Illinois. 
 
 ACKNOWLEDGEMENTS 
 
 We gratefully acknowledge the help of H. Kath- 
 leen Belcher and Michelle M. Georgi in data tabulation 
 and the contribution of Frank C. Bellrose and Robert 
 D. Crompton, who conducted the aerial censuses of 
 eagles. Funds for airplane rental were provided by 
 the Illinois Department of Conservation; U.S. Army 
 Corps of Engineers, St. Louis District; Illinois Power 
 Company; Commonwealth Fdison; and Central Il- 
 linois Public Service Company. Tabulation and 
 analysis of some of the data and preparation of this 
 report were supported in part by the Environmental 
 Research Program of the Department of Energy and 
 Natural Resources under C'ontrad Nos. EH-27 and 
 EH-2, and we thank Elizabeth Johnson and Linda 
 Vogt for their support. We also thank Dr. Glen C. 
 Sanderson, Head of the Section of Wildlife Research; 
 Drs. Richard and Jean Graber, and Dr. Christopher 
 D. Burnett of the Illinois Natural History Survey; Dr. 
 David L. Fischer, Brigham Young University; and Dr. 
 James B. Elder, who is retired from the L'.S. Fish and 
 Wildlife Service and lives in Minneapolis, Minnesota, 
 for reviewing the manuscript. Assistance for the final 
 manuscript was provided by Shirley McC'lellan, As- 
 sociate lechnital Editor; Lloyd Le Mere, lechnical 
 Illustrator; Molly Scott, Photographer; Patty Du/an, 
 computerization support and typesetting; Eva Steger, 
 typesetting; and Katie Roat. Illinois Natural History 
 Survey. We thank Dr. Fischer for the use of some of 
 his excellent photogi aphs. 
 
 Fig. 3 1. -Illinois nontoxic shot zones for the 1986 waterfowl hiunling 
 season. 
 
24 
 
 linois Natural History Survey Biological Notes 
 
 No 129 
 
 APPENDIX 
 
 Aerial inventory areas by region, number of inventories, mean number of bald eagles counted per inventory, 
 and maximum number of eagles censused during a single inventory at each area for all census years. (Number 
 of years of inventories in each region is listed in Table 4.) Asterisks indicate areas located in the Illinois River 
 
 floodplain but inventoried as part of the Lower Central Mi 
 
 ssissippi River Region. 
 
 
 
 
 Mean Number 
 
 Maximum Number 
 
 
 Number of 
 
 of Eagles 
 
 of Eagles 
 
 Inventory Area 
 
 Inventories^ 
 
 Per Inventory" 
 
 Censused 
 
 Upper Mississippi River Region 
 
 
 
 
 Dubuque-Galena River 
 
 22 
 
 6.5 
 
 25 
 
 Galena River-Bellevue 
 
 22 
 
 7.4 
 
 31 
 
 Bellevue-Green Island 
 
 22 
 
 16.4 
 
 39 
 
 Green Island-Savanna 
 
 22 
 
 11.8 
 
 28 
 
 Spring Lake Refuge 
 
 23 
 
 5.5 
 
 13 
 
 Elk River Refuge 
 
 22 
 
 4.1 
 
 18 
 
 Elk River— Fulton 
 
 23 
 
 11.3 
 
 23 
 
 Fulton-Albany 
 
 23 
 
 15.0 
 
 47 
 
 Albany-Wapsipinicon River 
 
 23 
 
 11.6 
 
 29 
 
 Wapsipinicon River-Princeton 
 
 23 
 
 20.9 
 
 68 
 
 Princeton-Interstate 80 
 
 23 
 
 7.4 
 
 28 
 
 Upper Central Mississippi River Region 
 
 
 
 
 Andalusia Refuge 
 
 49 
 
 1.8 
 
 47 
 
 Moline-Muscatine 
 
 124 
 
 4.9 
 
 27 
 
 Muscatine-Louisa 
 
 125 
 
 5.1 
 
 30 
 
 Louisa Refuge 
 
 127 
 
 5.1 
 
 24 
 
 New Boston 
 
 127 
 
 1.2 
 
 19 
 
 Keithsburg Refuge 
 
 131 
 
 2.9 
 
 14 
 
 Keithsburg-Oquawka 
 
 131 
 
 5.6 
 
 28 
 
 Oquawka Refuge 
 
 127 
 
 2.0 
 
 13 
 
 Crystal Lake 
 
 127 
 
 0.5 
 
 11 
 
 Oquawka-Burlington 
 
 131 
 
 5.5 
 
 52 
 
 Turkey Slough 
 
 128 
 
 0.9 
 
 8 
 
 Burlington— Dallas City 
 
 132 
 
 5.6 
 
 29 
 
 Dallas City-Fort Madison 
 
 133 
 
 4.9 
 
 19 
 
 Fort Madison-Nauvoo 
 
 133 
 
 7.5 
 
 37 
 
 Arthur Refuge 
 
 129 
 
 <0.1 
 
 3 
 
 Nauvoo- Keokuk 
 
 133 
 
 6.7 
 
 35 
 
 Lower Central Mississippi River Region 
 
 
 
 
 Keokuk-Meyer 
 
 130 
 
 11.7 
 
 90 
 
 Gardner Refuge 
 
 127 
 
 2.3 
 
 18 
 
 Meyer— Quincy 
 
 131 
 
 6.8 
 
 90 
 
 Quincy-Hannibal 
 
 125 
 
 5.0 
 
 57 
 
 Gardner Club 
 
 116 
 
 <0.1 
 
 3 
 
 Hannibal— Saverton 
 
 128 
 
 4.1 
 
 40 
 
 Shanks Refuge 
 
 126 
 
 2.9 
 
 18 
 
 Saverton-Louisiana 
 
 129 
 
 5.2 
 
 46 
 
 Delair Refuge 
 
 126 
 
 3.0 
 
 15 
 
 Sny Slough 
 
 127 
 
 0.8 
 
 39 
 
 Calumet Refuge 
 
 127 
 
 0.8 
 
 12 
 
 Duck Club 
 
 125 
 
 0.1 
 
 4 
 
 Cannon Refuge 
 
 126 
 
 2.8 
 
 13 
 
 Gilead 
 
 125 
 
 0.7 
 
 7 
 
 Batchtown Refuge 
 
 123 
 
 3.0 
 
 18 
 
 Batchtown Pool 
 
 123 
 
 6.3 
 
 52 
 
 Cuivre 
 
 124 
 
 2.1 
 
 16 
 
February 1988 
 
 Havera and Kruse: Winter Populations of Bald Eagles 
 
 2S 
 
 APPENDIX (continued) 
 
 Inventory Area 
 
 
 Mean Number 
 
 Maximum Number 
 
 Number 
 
 of Eagles 
 
 of Eagles 
 
 of Inventories* 
 
 Per Inventory" 
 
 Censused 
 
 124 
 
 3.8 
 
 26 
 
 124 
 
 1.1 
 
 13 
 
 123 
 
 1.3 
 
 9 
 
 126 
 
 2.0 
 
 20 
 
 127 
 
 2.8 
 
 13 
 
 127 
 
 13.6 
 
 269 
 
 128 
 
 1.8 
 
 18 
 
 131 
 
 0.7 
 
 10 
 
 108 
 
 0.9 
 
 8 
 
 109 
 
 0.8 
 
 13 
 
 109 
 
 1.8 
 
 20 
 
 109 
 
 3.6 
 
 25 
 
 109 
 
 6.0 
 
 38 
 
 109 
 
 8.5 
 
 46 
 
 108 
 
 12.5 
 
 53 
 
 105 
 
 15.1 
 
 64 
 
 11 
 
 2.4 
 
 8 
 
 59 
 
 0.6 
 
 5 
 
 59 
 
 1.6 
 
 10 
 
 59 
 
 2.4 
 
 12 
 
 59 
 
 4.4 
 
 21 
 
 123 
 
 0.5 
 
 6 
 
 123 
 
 0.8 
 
 11 
 
 123 
 
 1.2 
 
 11 
 
 124 
 
 <0.1 
 
 4 
 
 125 
 
 6.6 
 
 26 
 
 125 
 
 4.8 
 
 20 
 
 125 
 
 0.9 
 
 6 
 
 125 
 
 0.7 
 
 8 
 
 125 
 
 2.4 
 
 12 
 
 125 
 
 1.5 
 
 15 
 
 125 
 
 0.1 
 
 3 
 
 125 
 
 <0.1 
 
 3 
 
 125 
 
 0.9 
 
 8 
 
 125 
 
 3.8 
 
 14 
 
 123 
 
 0.8 
 
 7 
 
 123 
 
 <0.1 
 
 1 
 
 124 
 
 3.8 
 
 19 
 
 125 
 
 2.3 
 
 23 
 
 125 
 
 6.0 
 
 24 
 
 122 
 
 1.3 
 
 10 
 
 128 
 
 2.1 
 
 9 
 
 137 
 
 3.9 
 
 34 
 
 108 
 
 0.4 
 
 7 
 
 1 22 
 
 0.8 
 
 6 
 
 120 
 
 1.8 
 
 17 
 
 Dardenne 
 
 Marais Temps Clair 
 
 Hager 
 
 Grafton-Alton 
 
 Gilbert Lake* 
 
 Flat Lake, Swan Lake* 
 
 Stump Lake* 
 
 Godar Swamp* 
 
 Lower Mississippi River Region 
 Horseshoe Lake 
 St. Louis-Kimmswick 
 Kimmswick— Crystal City 
 Crystal City— Ste. Genevieve 
 Ste. Genevieve-Chester 
 Chester-Grand Tower 
 Grand Tower-Cape Girardeau 
 Cape Girardeau— Cairo 
 
 Upper Illinois River Region 
 
 Morris-Seneca 
 
 Seneca— Marseilles 
 
 Marseilles-Utica 
 
 Utica-La Salle 
 
 La Salle-Spring Valley 
 
 Central Illinois River Region 
 Turner Lake 
 DepueLake, Spring Lake 
 Coleman Lake 
 Bureau Ponds 
 Goose Lake 
 Senachwine Lake 
 Siebold Lake 
 Sawmill Lake 
 Billsbach Lake 
 Weis Lake 
 Sparland Lake 
 Wightman Lake 
 Sawyer Slough 
 Hitchcock Slough 
 Round Pond 
 Meadow Lake 
 Rice P(jnd 
 Goose Pond 
 Upper Peoria Lake 
 Lower Peoria Lake 
 
 Lower Illinois River Region 
 
 Pekiii Lake 
 
 Poweiton Lake 
 
 .Spring Lake 
 
 Banner Marsh 
 
 Duck Creek Cooling Lake 
 
Illinois Natural History Survey Biological Notes 
 
 APPENDIX (continued) 
 
 
 
 Mean Number 
 
 Maximum Number 
 
 
 Number 
 
 of Eagles 
 
 of Eagles 
 
 Inventory Area 
 
 of Inventories^ 
 
 Per Inventory" 
 
 Censused 
 
 Rice Lake 
 
 134 
 
 2.2 
 
 11 
 
 Big Lake 
 
 134 
 
 3.0 
 
 14 
 
 Goose Lake 
 
 131 
 
 0.8 
 
 9 
 
 Clear Lake 
 
 134 
 
 6.0 
 
 28 
 
 Chautauqua Lake 
 
 135 
 
 9.4 
 
 35 
 
 Quiver Creek 
 
 136 
 
 4.1 
 
 23 
 
 Quiver Lake 
 
 110 
 
 0.7 
 
 10 
 
 Bath Lake 
 
 127 
 
 1.0 
 
 11 
 
 Grass Lake 
 
 133 
 
 1.6 
 
 10 
 
 Anderson Lake 
 
 134 
 
 1.3 
 
 9 
 
 Moscow Bay 
 
 135 
 
 0.9 
 
 9 
 
 Jack Lake 
 
 135 
 
 5.2 
 
 23 
 
 Snicarte Slough 
 
 135 
 
 0.6 
 
 7 
 
 Ingram Lake 
 
 135 
 
 1.8 
 
 13 
 
 Stewart Lake 
 
 132 
 
 0.9 
 
 11 
 
 Crane Lake 
 
 134 
 
 8.1 
 
 29 
 
 Cuba Island 
 
 133 
 
 5.5 
 
 40 
 
 Chain Lake 
 
 133 
 
 2.0 
 
 16 
 
 Sangamon Delta 
 
 132 
 
 4.3 
 
 33 
 
 Treadway Lake 
 
 132 
 
 1.1 
 
 12 
 
 Muscooten Bay 
 
 69 
 
 0.2 
 
 3 
 
 Big Prairie Lake 
 
 131 
 
 0.9 
 
 12 
 
 Meredosia Lake 
 
 133 
 
 4.9 
 
 25 
 
 Smith Lake 
 
 130 
 
 0.6 
 
 11 
 
 Central and Southern Lakes Region 
 
 
 
 
 DeWitt County 
 
 
 
 
 Clinton Lake 
 
 14 
 
 0.0 
 
 
 
 Sangamon County 
 
 
 
 
 Lake Springfield 
 
 56 
 
 0.8 
 
 7 
 
 Christian County 
 
 
 
 
 LakeSangchris 
 
 59 
 
 0.3 
 
 3 
 
 Montgomery County 
 
 
 
 
 Cof feen Lake 
 
 41 
 
 0.4 
 
 5 
 
 Shelby and Moultrie counties 
 
 
 
 
 Lake Shelbyville 
 
 31 
 
 0.4 
 
 3 
 
 Jasper County 
 
 
 
 
 Newton Lake 
 
 26 
 
 0.6 
 
 6 
 
 Clinton and Fayette counties 
 
 
 
 
 Carlyle Lake 
 
 56 
 
 2.2 
 
 9 
 
 Jefferson and Franklin counties 
 
 
 
 
 Rend Lake 
 
 55 
 
 1.8 
 
 9 
 
 Randolph County 
 
 
 
 
 Baldwin Lake 
 
 58 
 
 0.4 
 
 5 
 
 Northeast Lakes Region 
 
 
 
 
 McHenry County 
 
 
 
 
 McHenry Dam vicinity 
 
 31 
 
 1.4 
 
 7 
 
 Wonder Lake 
 
 28 
 
 0.3 
 
 3 
 
 Woodstock Ponds 
 
 28 
 
 0.0 
 
 
 
 Pistakee Bay 
 
 30 
 
 0.2 
 
 5 
 
 Lake County 
 
 
 
 
 Fox Lake 
 
 30 
 
 0.3 
 
 3 
 
February 1988 
 
 Havera and Kruse: Winter Populations of Bald Eagles 
 
 27 
 
 APPENDIX (continued) 
 
 Inventory Area 
 
 Number 
 of Inventories ' 
 
 Mean Number 
 
 of F.agles 
 Per Inventory'' 
 
 Maximum Nuiulier 
 of Eagles 
 C'.ensused 
 
 Grass Laice 
 
 Antioch-Laice Villa 
 DeKalb County 
 
 Shabbona Lake 
 Cook County 
 
 Crabtree Nature Area 
 
 Baker Lake vicinity 
 
 McGinnis Slough vicinity 
 
 McGinnis— Calumet 
 Will County 
 
 Des Plaines Wildlife Area 
 
 Rendwick Lake vicinity 
 Grundy County 
 
 Dresden Lake 
 
 Goose Lake Prairie 
 
 Collins Lake 
 
 Braidwood Lake 
 La Salle County 
 
 Seneca Lake 
 
 Surface-mined Lakes Region 
 
 Knox County 
 
 Victoria vicinity 
 
 Rapatee vicinity 
 
 Peabody property 
 Fulton County 
 
 Norris vicinity 
 
 Fairview vicinity 
 
 Fin and Feather property 
 
 CI LCO property 
 
 Buckheart property 
 
 Cebuhar property 
 
 Justice property 
 
 Metropolitan Sanitary 
 District property 
 
 Fulton County C^onservation Area 
 
 Cuba vicinity 
 
 Wee-Ma-Tuk property 
 
 Red Barn property 
 
 Giant Goose Ranch property 
 
 Lower KashtLskia Kii <er Region 
 Fayetteville— New Athens 
 New Athens-Rt. 154 
 Rt. 154-F.vansville 
 Kvansville-Cihester 
 
 30 
 30 
 
 25 
 
 31 
 31 
 
 42 
 40 
 
 46 
 41 
 
 47 
 47 
 47 
 44 
 
 45 
 
 16 
 22 
 22 
 
 22 
 22 
 22 
 23 
 23 
 23 
 23 
 
 23 
 23 
 23 
 23 
 23 
 23 
 
 7 
 7 
 7 
 7 
 
 0.3 
 
 0.0 
 
 0.0 
 
 0.3 
 
 <0.1 
 
 0.9 
 
 0.2 
 
 <0.1 
 <0.1 
 
 0.2 
 0.6 
 0.5 
 0.5 
 
 0.2 
 
 0.0 
 0.0 
 0.0 
 
 ().() 
 0.0 
 0.0 
 2.3 
 0.5 
 0.0 
 0.0 
 
 0.3 
 ().() 
 0.0 
 
 o.n 
 
 0.(1 
 0.0 
 
 0.0 
 
 0.1 
 0.3 
 1.4 
 
 
 
 
 
 
 
 
 
 10 
 2 
 
 
 
 3 
 
 
 
 
 
 
 
 1 
 2 
 6 
 
 ■'Based oil the period Ixiwecii llic liisi si^hling of a bald eagle in llie lall of eath year and ihc lasl sighting in ihc lf)ll<>\ving spring, 
 and not llie entire (ensiis period troin f.ill through spring. 
 
Illinois Natural History Survey Biological Notes 
 
 No. 129 
 
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