MONTHLY WIILLIFE RESEARCH LETTER 
Department of Conservation and Natural History Survey, Cooperating 
T. G. Scott, Editor 
Urbana, Illinois 
June 1959 
Vol. 2, No. 6 
W-30-R-12 R. F. Labisky 
An indication of accelerated postnesting mortality of pheasant hens 
can be obtained by determining the proportion of broods unaccompanied by hens 
during late summer. The causes of postnesting mortality of pheasant hens may 
be associated with the physiology of the hens. Studies in Wisconsin with penned 
birds have shown that the hen reaches an annual, physiological low in midsummer, 
which apparently results from accumulated stresses caused by nesting and molting. 
Thus, it is reasonable to assume that prolonged nesting seasons could cause a 
higher rate of late-summer mortality of hens because of extended physiological 
stress. 
Findings from the Sibley area indicated a brood-hen mortality of 3.0 
per cent in 1956, 11.U per cent in 1957, and 5.7 per cent in 1958. (Broods that 
were 10 or more weeks in age, but unaccompanied by hens, were excluded from 
these data because behavior observations have shown that brood members are 
"weaned" at about 10 weeks of age.) The establishment of nests by pheasant hens 
spanned a period of 15 weeks in 1957 and 11 weeks in 1958; similar data are not 
available for 1956, but the nesting season was considered to be shorter (or 
earlier) than those of 1957 and 1958. These findings support the premise that 
accelerated postnesting mortality of hens coincides with extended nesting 
seasons. 
W-U2-R-8 R. D. Lord 
Sixty-five early-morning roadside censuses and 29 nighttime spotlight 
censuses were made from May, 1957 to December, 1958. In both years more rabbits 
were seen per mile during the spotlight census than during the early-morning 
census, except during the 3 summer months. May, June, and July. 
Data for approximately 2 months of activity of caged rabbits, based 
on a recorder connected to a treadle in an out-of-doors cage, indicate a shift 
from a decidedly nocturnal pattern to a 2ii-hour pattern with early-morning and 
evening peaks. Six all-night roadside censuses extending into daylight made 
during the past 3 months, on a 22 mile route at an average speed of 22 mph 
indicate a correlation between activity trends in roadside activity and activity 
trends based on the activity-recorder. 
Reproduction (prevalence of pregnancy and average litter size) of 
cottontails was calculated from samples of rabbits of all ages taken each month 
of the breeding season. As the age of the rabbits increased there was an 
OCT 9 1959 
NATURAL 
HISTORY SURVEY 
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