Herbivore Body Condition Response in Altered Environments: Mule Deer and Habitat Management

Abstract

The relationships between habitat, body condition, life history characteristics, and fitness components of ungulates are interwoven and of interest to researchers as they strive to understand the impacts of a changing environment. With the increased availability of portable ultrasound machines and the refinement of hormonal assays, assessment of ungulate body condition has become an accessible monitoring strategy. We employed body condition scoring, estimation of % ingesta-free body fat (%IFBF), assessment of free thyroid hormones (FT4 and FT3), and assessment of pregnancy, as metrics to determine if landscape-level habitat treatments affected body condition of adult (≥1.5 years old) female mule deer (Odocoileus hemionus). All body condition related metrics were measured on 2 neighboring study areas — a reference area that had received no habitat treatments and a treatment study area that had received mechanical removal of pinyon pine (Pinyus edulis) - Utah juniper (Juniperus osteosperma) forest, chemical control of weeds, and reseeding with preferred mule deer browse species. A consistent trend of higher %IFBF was observed in the treatment study area than in the reference study area , although variation of estimates was larger than hypothesized. A similar pattern was observed with higher thyroid hormones concentrations being observed in the treatment study area, but large amounts of variation within concentration estimates were also observed. The consistent pattern of higher body condition related estimates in our treatment study area provides evidence that large mammalian species are sensitive to landscape change, although variation within estimates underlie the challenge in detecting population level impacts stemming from environmental change.

Variation in ungulate body fat: Individual versus temporal effects

“…Similarly, we had no way of knowing which animals may have nursed twins and for how long, 2 factors that are influential to individual condition (i.e., as evidenced by observation of adult female deer with fawns during fall being highly influential for individual condition; Monteith et al ). Previous authors have noted that pregnancy status at the time of capture can be correlated with body condition, although those correlations have tended to be weak (Bishop et al , , Monteith et al , Bergman et al ). The correlation is weak likely because pregnancy rates in mule deer, especially in western Colorado, tend to be high and largely invariant (Bishop et al , ; Bergman et al ).…”

“…More recent methods have coupled standardized palpation scores with ultrasonographic measurements to generate live animal body fat estimates (Cook et al , ). The product of this process is an estimate of the percent ingesta‐free body fat (%IFBF) for an animal, a parameter that has become more commonly used as a metric in studies of potential management actions (Bishop et al , ; Bergman et al ), as a tool to evaluate anthropogenic influences on wildlife (Lendrum et al , Northrup et al ), and as a tool to better understand life history (Monteith et al , ; Searle et al ). Through analyzing this relatively new stream of data, we have learned that %IFBF, and presumably overall condition, among individual animals, even those taken from the same herd at that same time, is highly variable (Bergman et al ).…”

Mule Deer Habitat Selection Following Vegetation Thinning Treatments in New Mexico

“…Treating habitat can improve deer forage quality and body condition, but selection for treated areas can vary considerably by season and year (Everitt 1983, Hobbs and Spowart 1984, Bergman et al 2014 b , Sorensen 2015). Additionally, posttreatment recovery time and climatic conditions interact to influence vegetation responses to tree thinning.…”

Habitat and herbivore density: Response of mule deer to habitat management

“…Mechanical habitat treatments were delivered within the previous 2–8 years (Bergman et al ). We did not incorporate potential study units that had received mechanical treatments within the previous 1–2 years because of uncertainty about time lags in vegetation response following mechanical disturbance.…”

“…We captured mule deer and marked them as part of a larger research project (Bergman et al ). We captured all deer either by helicopter net‐gunning (Webb et al , Jacques et al ) or baited drop‐nets (Ramsey , Schmidt et al , White and Bartmann ).…”