9th International Deer Biology Congress

AUTHORS: Jacob H. Kay, New Mexico State University, Department of Fish Wildlife and Conservation Ecology; James W. Cain III, U.S. Geological Survey, New Mexico Cooperative Fish and Wildlife Research Unit, New Mexico State University, Department of Fish Wildlife and Conservation Ecology; Stewart G. Liley, New Mexico Department of Game and Fish

ABSTRACT: Ungulates commonly select habitat with higher edible forage biomass and nutritional quality to maximize individual fitness [1]. However, predators can indirectly alter ungulate habitat selection and foraging behavior, and consequently their nutritional condition [2]. Ungulates will often choose areas with decreased predation risk, sometimes sacrificing higher quality forage [3]. This tradeoff between ideal forage and predation risk can be an important life strategy with major effects on body condition of individuals, and subsequently population vital rates. We determined if this tradeoff existed in a mule deer (Odocoileus hemionus) population in central New Mexico, and then examined mule deer habitat selection to see how they approached it. We utilized GPS collar data to model mule deer habitat selection based on covariates that included multiple metrics for forage as well as measurements of stalking cover and predation risk. We also examined microsite characteristics of mountain lion kill sites and mule deer foraging points to assess tradeoffs at a finer scale. Our data showed a moderate correlation (r = 0.43) between forage biomass and stalking cover, which indicates that deer are faced with a tradeoff between forage and risk. We also found that deer selection of foraging sites was best explained by increased quantities of edible biomass, further supporting the potential for a tradeoff scenario. As a whole, deer selected for areas of higher edible biomass when mountain lion predation risk and stalking cover were lower. Likewise, they utilized areas with lower stalking cover when predation risk was higher, also indicating that risk affects their behavior. Additionally, we found that actual kill sites were best explained by increasing stalking cover and grams of digestible protein, suggesting deer may be selecting for forage quality at the cost of predation risk. The mean visibility (i.e. stalking cover) at kill sites was 10.47m (± 0.94 [95%CI]) compared to 14.43m (± 1.63) at random points, and a site was 1.5 times more likely to be a kill site with each 1-meter decrease in visibility. The often inconspicuous indirect effects of predation usually manifest themselves as nutrition deficiencies have a high potential to be mistaken for bottom-up forcing, which could lead to a misinterpretation of results and subsequently to flawed management strategies.