DOI: 10.5061/dryad.v41ns1s28
title: Movement and nutritional data of mule deer in Western Wyoming (December 2015–March 2021)

description: For many species, behavioral modification is an effective strategy to
 mitigate negative effects of harsh and unpredictable environmental
 conditions. When behavioral modifications are not sufficient to mitigate
 extreme environmental conditions, intrinsic factors may be the primary
 determinant of overwinter survival. We investigated how movement behavior,
 and internal (i.e., nutrition and age) and external (i.e., food
 availability and snow depth) states affect survival over winter of a
 long-lived and highly faithful species (mule deer; Odocoileus hemionus).
 We first tested if animals changed their behavior during winter based on
 internal and external states; we subsequently investigated how behavior
 and state interacted to influence survival risks in the face of
 extraordinary winter conditions. Movement behavior changed minimally as a
 function of age and nutrition; and yet, movement behavior affected
 survival—animals that exhibited more restricted movements were more likely
 to succumb to mortality overwinter compared with animals with less
 restricted movements. Additionally, nutrition and cumulative snow depth
 had a strong effect on survival; animals that were exposed to deep snow
 and began winter with low fat were much less likely to survive. Behavior
 was an effective tool in securing survival during mild or moderate
 winters, but nutrition ultimately underpinned survival during harsh
 winters.
description: We studied a population of mule deer that winters on two distinct
 winter ranges in the Wyoming and Salt River mountain ranges in western
 Wyoming, USA (42°25°N, 110°42°W) from December 2015 to March 2021. Adult,
 female mule deer were fit with GPS collars that recorded fixes every 2
 hours. We used data on movement, nutritional condition,
 age, and survival of adult (≥2 yrs old), female mule deer from December
 2015 to March 2021. Beginning in December 2015, we captured 70 adult,
 female mule deer using helicopter net gunning. Each March and December
 following that initial capture, we recaptured all surviving individuals
 and captured new individuals to maintain a sample size of 70 animals. At
 the initial capture event, we extracted one insiciform canine to assess
 age of individuals using cementum annuli and assigned a unique animal
 identifier (e.g., “001”). At every capture event, we measured body mass,
 determined nutritional condition, and fit all animals with a GPS
 radio-collar programmed to take satellite fixes every two hours from
 December 2015 to March 2018 and every one hour from December 2018 to March
 2021 (LaSharr et al. 2022). Nutritional condition of individuals was
 determined using developed protocols for mule deer which include measuring
 subcutaneous rump fat via ultrasonography and body palpation to estimate a
 body condition score (Stephenson et al. 2002; Cook et al. 2007). We
 calculated percent ingesta-free body fat (hereafter, body fat) of all
 animals (Cook et al. 2007). For each winter, animals were assigned a
 unique animal-year identifier. GPS collars recorded locations every 1 to 2
 hours throughout winter. First, we subset all collars that had hourly
 relocation data to 2 hours. Next, we subset movement data for each winter
 for each individual from 1 December to 30 April. Because we were
 interested in movement on winter range, and not during migration, if
 animals were still migrating into the beginning of December, we began the
 subset on the day following their last migration date in autumn. If
 animals began migrating in April, we ended the subset the day before their
 first migration date in spring. If animals spent more than 50% of December
 or April migrating, we removed those animal-years from the
 analyses.