Risk Factors and Mortality of Black-Tailed Deer in a Managed Forest Landscape

Abstract

We investigated the influence of habitat use on the risk of death of Sitka black-tailed deer (Odocoileus hemionus sitkensis) on Heceta Island in Southeast Alaska, USA. A mosaic of even and uneven-aged forests covered much of the island and provided a model setting in which to assess relationships between habitat use and mortality of deer. We radiocollared and monitored 51 adult females, 11 adult males, and 19 young of the year. We compared risk of death with habitat composition, habitat distribution, topography, distances to features such as roads, and functional habitat characteristics such as seasonal forage biomass within 50-, 500-, and 1,000-m circular buffers around relocations of deer. Those buffers encompassed habitats used at scales of radio-locations, home ranges, and landscapes. We addressed hypotheses that related habitat composition and distribution to risk of death from malnutrition, predation, and hunting. Predation by wolves (Canis lupus) and malnutrition were the principal causes of death of adult females and young, whereas hunters killed most adult males. Habitat factors at scales of 500 and 1,000 m had the greatest effect on mortality of adult females and young, whereas habitat characteristics in the immediate vicinity of radio relocations had the greatest effect on mortality of adult males. Malnutrition was positively associated with use of forage-poor habitats such as pole-stage, second-growth forest. Use of precommercially thinned second growth increased risk of death for young deer. Use of level terrain was the most influential factor with respect to predation and increased risk of death at all scales. Use of open habitats, such as muskegs and young clearcuts, also increased risk of death. Use of shrub-sapling-stage clearcuts in landscapes accessible by roads increased risk of death from hunting. We showed that use of specific habitats and the landscape context of those habitats were important factors influencing mortality of deer. We also demonstrated the importance of comparing habitat use with measures of fitness rather than simply with availability when evaluating habitat suitability for deer. Our results should be useful to wildlife researchers investigating contributions of habitat to fitness and population dynamics of ungulates, and to wildlife managers attempting to manipulate habitats to benefit deer populations.