Understanding margins of safe capture, chemical immobilization, and handling of free-ranging white-tailed deer

Improved understanding of the margins of safe capture, chemical immobilization, and handling of free-ranging animals for research and management relies on the documentation and examination of efforts involving various species, study designs, and environmental conditions. During 1991-2002 we had 984 captures and recaptures of white-tailed deer (Odocoileus virginianus), primarily by Clover trap, under a wide range of winter weather conditions and in an area saturated with wolves (Canis lupus). We captured and recaptured 337 radiocollared females (0.5-15.5 years old) 652 times. Total capture-related mortality was 5.4% (35 of 652). The incidence of capture accidents (e.g., trauma-induced paralysis, death) was 2.9%, and mortality that occurred within 14 days of release was 2.5%. Mean time to mortality for this latter group was 6 days (SE = 1.1 days, n = 16); wolf predation within 11 days was the proximate cause of 50% of these mortalities. A priori, we selected immobilization time for analysis by logistic regression to test for a potential effect of capture and handling on mortality while controlling for known risk factors (age, winter severity) but found no significant effects. Additionally, subsequent comparisons of means and standard errors (SEs) showed no differences among numerous aspects of the capture, immobilization, handling, or associated weather conditions. Success in capture and handling of free-ranging deer results in smaller sample sizes of capture-related deaths (i.e., events), which makes it difficult to infer causal relations between environmental variables, handling procedures, and capture-related mortality. The strength of such studies is that they may serve to demonstrate a range of conditions (environmental variables and handling procedures) over which capture-related mortality can be controlled at acceptably low levels.