MONTHLY WILDLIFE RESEARCH LETTER 
Department of Conservation and Natural History Survey, Cooperating 
T. G. Scott, Editor 
Urbana, Illinois 
May I960 
Vol. 3, No. 5 
W-30-R-13 R. F. Labisky 
Age ratios among pheasant hens captured by night-lighting on the Sibley 
area during pre- and posthunting season periods have yielded some interesting 
findings concerning differential mortality of the age groups. The ratio of young 
hens per adult hen changed from a prehunt figure of 3.4 to a posthunt (January) 
figure of 1.9 in 1956-57, which represents a relative decline of 44.1 per cent 
among young hens during fall and early winter if no loss of adults occurred. It 
is probable that there was some loss among adults, making the probable loss of 
young hens greater than 44 per cent. Comparable data for 1957-58 showed a change 
from 1.5 to 1.0 young hens per adult hen from preseason to postseason, or a rel¬ 
ative decline of 33.3 per cent among young hens. These findings suggest a high 
degree of mortality among hens during fall and early winter, which is primarily 
at the expense of young birds. However, in 1958-59, this phenomenon of mortality 
was reversed as the preseason to postseason ratio of young hens per adult hen 
increased from 2.3 to 2.7. Collectively, these data suggest that the mortality 
of pheasant hens during this period of the year is an important factor of pop¬ 
ulation ecology of this species, and, consequently, deserves further investigation. 
W-42-R-9 R. D. Lord, Jr. 
Another new disease of cottontail rabbits, distinct from Ferris’s disease 
(also found by this project), has recently become apparent. Fifty-three rabbits 
were received from Loren Fits this past winter. Some one or several of these 
rabbits contained a highly pathogenic organism which ultimately wiped out the entire 
group though they had been separated into two colonies. The disease then spread to 
rabbits that had been in captivity for 8 to 10 months, and 15 captive rabbits have 
succumbed to this disease. 
Externally the symptoms of the disease are a diarrhea resulting in a wet 
and dirty appearance of the fur in the anal region and on the back side of the hind 
legs. Internally the disease causes kidney and liver damage and peptic ulcers of 
the stomach very similar to those found in man. 
The disease has been successfully transmitted in the laboratory from 
rabbits that died of it to other rabbits and hamsters. Because attempts to grow 
the disease organism on bacterial culture plates have failed, a virus is indicated 
as the causative organism. Any biolgist or conservation officer observing this 
disease in the field should contact the project leader. 
JUN 16 1960 
natural 
history survey 
library 
