Table 3. Frequency of occurrence of food species in 600 
cast pellets of bald eagles (300 each in 1975-76 and 
1976-77), Swan Lake National Wildlife Refuge. 


Category and species 1975-76 1976-77 = Total 
Birds 
Canada goose 
(Branta canadensis) 286 24] 527 
Snow goose 
(Chen caerulescens) 8 15 23 
Mallard 
(Anas platyrhynchos) 81 130 211 
Pintail 
(Anas acuta) 2 1 3 
Green-winged teal 
(Anas crecca) 0) 3 3 
American coot 
(Fulica americana) 3 § 11 
American bittern 
(Botaurus lentiginasus) 0 ] 1 
Mammals 
White-tailed deer 
(Odocoileus virginianus) 0 1 1 
Muskrat 
(Ondatra zibethicus) 4 2 6 
Cottontail 
(Sylvilagus floridanus) 9 2 11 
Raccoon 
(Procyon lotor) 1 0 1 
Fox squirrel 
(Sciurus niger) 1 0 1 
Deer mouse 
(Peromyscus maniculatus) 0 2 2 
Fish 25 10 35 


Local Movements of Eagles 
Local movements of 18 radio-tagged bald eagles were 
monitored, 6 in 1975-76 and 12 in 1977-78 (Table 4). In 
1975-76, the radio-tagged birds were in the study area for 
periods of 5 to 63 days (average, 35 days). There were 158 
radio locations and 11 visual sightings of tagged birds from 
2 January to 23 March. There were no known transmitter 
failures or losses. In 1977-78, the radio-tagged eagles were 
in the study area for at least 6 to 75 days (average, 43 
days). From 9 January through 6 April, there were 375 
radio locations and 5 visual sightings of these 12 birds. 
During this period, three transmitter units failed and three 
others fell off the birds. 
Radio-tagged eagles that stayed in the study area occu- 
pied Swan Lake NWR, Fountain Grove Wildlife Manage- 
ment Area, Pershing State Park, and bottomland along the 
Grand River (Fig. 1), Few radio locations were made in 
upland sites outside these four areas. Minimum estimated 
local winter ranges varied from 3.3 to 69.0 km? for radio- 
tagged eagles that remained on the study area for at least 
22 days. Ranges encompassed most waterfowl concentra- 
tion points within the entire study area, suggesting that 
eagle movements were strongly influenced by waterfowl 
dispersal patterns. 
During both field seasons, movements of individual 
eagles varied greatly. Of the 18 radio-tagged birds, we 
located 6 only at Swan Lake NWR; 2 at Swan Lake NWR 
and bottomland along Grand River; 9 at Swan Lake 
NWR, Grand River bottomlands, and Fountain Grove 
Wildlife Management Area; and 1 at these three areas plus 
Pershing State Park. A few eagles frequently moved 
between Swan Lake and Fountain Grove, but generally 
the birds fed during the day and roosted at night on the 
same area. For example, in 1976 one eagle was on Swan 
Lake on 16 and 17 January, moved to Fountain Grove on 
19 January for 3 days, moved back to Swan Lake for 2 
days, returned to Fountain Grove for 16 days, and re- 
turned to Swan Lake for 14 days, until 24 February when 
it left the study area and radio contact was lost. Birds 
sometimes flew from Fountain Grove to feed on Swan 
Lake during the day, then returned to Fountain Grove to 
roost for the night. At other times, eagles fed on Swan 
Lake during the day and roosted near the river west of the 
refuge at night. Distances between feeding areas and night 
roost sites never exceeded 15.3 km. 
Table 4. Numbers of radio locations, visual sightings, 
days in study area, and minimum local winter ranges of 
radio-tagged bald eagles, Swan Lake National Wildlife 
_ Refuge, 1975-76 and 1977-78. 


Year, and Radio Visual Daysin Minimum 
eagle no, locations sightings area range (km?) 
1975-76 
1 4 0) 5 18.9 
2 34 4 63 69.0 
3 5 1 11 13.8 
4 24 3 30 26.1 
5 33 3 39 59,1 
6 58 0 61 42.5 
1977-78 
7a 6 2 10 7.2 
8a 2 1 6 - 
gb 39 0 38 3.3 
10 42 0 58 12.3 
1] 53 0 56 4.2 
12 48 0 75 35.7 
13 42 ] 71 9.0 
14b 31 0 38 11.9 
15a 27 ] 50 24.6 
16» 40 0 46 32.8 
17 20 0 22 19.6 
18 25 0 47 31.2 

“Transmitter unit stopped operating. 
bTransmitter unit fell off eagle. 
