Because most mortality occurs during winter, estimation of overwinter
survival rates is needed for sensible management of winter-stressed un
gulates. We developed general estimators and determined overwinter sur
vival rates of mule deer (Odocoileus hemionus) in southcentral Wyoming
, from pre- and post-winter age ratio samples of the population, and a
ge ratios of carcasses found in the spring. Both adult and fawn overwi
nter survival rates can be estimated if all 3 of these ratios are avai
lable. Adult survival varied from 0.798 (SE 0.103) in 1985-86 to 0.908
(SE 0.030) in 1988-89. For these same winters, fawn survival was 0.66
5 (SE 0.103) and 0.631 (SE 0.037). Critical assumptions are that estim
ates of age ratios are unbiased or have the same bias in all 3 surveys
, and that reliable estimates of the variances of these ratios are obt
ained. Sample size calculations based on a binomial distribution are p
resented for the estimators provided.