Vo 1. 25, No. 7 
Page 4 
We noted that by the 5th or later nest season following burning, nest 
densities for avian nesters overall had returned to densities similar to that 
in unburned or recently burned prairie grass. Our data for prairie grass 
management suggest that a combination of prescribed burning at intervals of 3-5 
years and high mowing is beneficial to prairie chickens and to a variety of 
grassland nesters. However, we need to evaluate limited grazing as a substitute 
for rotary mowing because of the constraints imposed by energy conservation and 
economics. Haying of prairie grasses may have merit but probably at intervals 
not more frequent than 3 years. 
jcology. and. Management of White-tailed Deer - W- 87 -R C.M. Nixon, L.P. Hansen, 
J.E. Chelsvig, P.A. Brewer 
Many studies of male deer dispersal have found that males, particularly 
yearlings, tend to disperse in the fall when social pressure from breeding 
activity is greatest. It was concluded that this pressure is the stimulus that 
causes the males to disperse. 
Observations during the present study show that bucks disperse in the spring 
when there is no breeding activity. The stimulus for spring dispersal is 
uncertain, but in the case of male fawns, dispersal may be triggered by the 
mother's aggressive behavior while trying to isolate herself for fawning. 
Hormonal changes in the bucks may also provide a dispersal stimulus. Other 
researchers have found slight increases in serum androgen levels in male deer 
during April and May that coincide with the onset of antler development. 
According to our observations, these months are also the time of spring dispersals. 
Although aggressive behavior and hormonal changes may not be the reasons 
that male deer disperse from apparently suitable habitat into unfamiliar areas, 
these factors seem to be important in determining the time at which the movement 
occurs. 
Cooperative Waterfowl Research - W-88-R F.C. Bell rose, S.P. Havera, 
G.A. Perkins, H.K. Archer 
The aerial waterfowl censuses, conducted each fall and spring by Robert 
Crompton, provide an opportunity to monitor population changes of endangered bald 
eagles while they overwinter in Illinois. Because the eagles feed primarily on 
fish, they concentrate along the Illinois and Mississippi rivers. The eagles 
are often difficult to see when perched in trees, but Crompton believes that he 
censuses approximately 75% of them. 
In 1981, eagles began moving into Illinois from their northern breeding 
grounds during late September—1 month earlier than in 1980. Eagle numbers in 
the Illinois River valley between Spring Valley and Grafton reached a peak of 
223 birds during the 1st week of March. This compares with peaks of 166, 2^0, 
361, and 265 birds for the winters of 1976-77, 1977*78, 1978-79, and 1980-81, 
