Age-Specific Causes of Mortality among Male White-Tailed Deer Support Mate-Competition Theory

Mate-competition theory predicts that males will invest resources toward intrasexual competition for mates until reproductive benefits are outweighed by costs to future fitness. In populations that have a substantial proportion of mature males, theory predicts that young males will forego reproduction to reduce exposure to mortality that may result from breeding efforts. We examined age-specific mortality of males in a white-tailed deer (Odocoileus virginianus) population in which >50% of the males were ≥3.5 years old to determine whether patterns of male mortality conform to mate-competition theory. Annual mortality rates were relatively stable throughout adulthood (0.26-0.38), but causes of mortality changed with age. Young males (1.5 and 2.5 years old) were most susceptible to human-induced mortality (e.g., hunting and vehicle accidents), whereas males ≥3.5 years old tended to die from non-human causes (e.g., fighting, predation) more frequently than did younger deer. Proportional hazard models also indicated that as antler size increased, likelihood of mortality increased. Age- and cause-specific patterns of mortality in adult male deer from a population with >50% mature males reflected patterns predicted by mate-competition theory. When managing deer populations with high proportions of mature males, it is important to account for shifts in susceptibility to human-induced and natural mortality agents.