Changing migratory patterns in the Jackson elk herd

Abstract

Migratory behavior in ungulates has declined globally and understanding the causative factors (environmental change vs. human mediated) is needed to formulate effective management strategies. In the Jackson elk herd of northwest Wyoming, demographic differences between summer elk (Cervus elaphus) population segments have led to changes in migratory patterns over a 35-year time period. The proportion of short-distance migrants (SDM) has increased and the proportion of long-distance migrants (LDM) has concurrently declined. The probability of winter-captured elk on the National Elk Refuge being LDM decreased from 0.99 (95% CI ¼ 0.97-1.00) to 0.59 (95% CI ¼ 0.47-0.70) from 1978 to 2012. We tested 4 hypotheses that could contribute toward the decline in the LDM segment: behavioral switching from LDM to SDM, differential survival, harvest availability, and calf recruitment. Switching rates from LDM to SDM were very low (0.2% each elk-year). Survival rates were similar between LDM and SDM, although harvest availability was relatively low for SDM that tended to use areas close to human development during the hunting season. Average summer calf/cow ratios of LDM declined from 42 to 23 calves per 100 cows from 1978 -2012 . Further, during 2006 -2012, LDM summer calf/cow ratios were less than half of SDM (23 vs. 47 calves per 100 cows). Our data suggest recruitment is the driving factor behind the declining proportion of LDM in this region. Effectiveness of altering harvest management strategies to conserve the LDM portion of the Jackson elk herd may be limited. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.

Behavioural flexibility in migratory behaviour in a long‐lived large herbivore

“…In one of the only other studies examining switching over time in elk, Cole et al . () found little evidence for switching between migratory strategies for 129 elk monitored >2 years in the Jackson Hole elk herd. One obstacle in comparing our results to theirs is that Cole et al .…”

“…), ~10% for impala (Gaidet & Lecomte ), and 0·2% from short‐distant to long‐distant migrant elk (Cole et al . ) almost certainly underestimate true switching rates. Therefore, population modelling for partially migratory ungulates may need to account for switching between strategies.…”

“…One obstacle in comparing our results to theirs is that Cole et al . () used a different approach to classify migratory behaviour in their system, and there were no clear residents. Thus, methodological differences in the classification of migration may still be obscuring switching between strategies.…”

Challenges and science-based implications for modern management and conservation of European ungulate populations

“…Recently, a decrease in the migration rate of several species has been observed (Harris et al 2009;Cole et al 2015). Climate change, anthropogenic pressure and possibly changes in predator-prey dynamics have all been indicated as potential drivers of this decline.…”

Land management alters traditional nutritional benefits of migration for elk

“…Different behaviors can allow individuals to achieve equal fitness, consistent with predictions of partial migration as an ideal free distribution (Fretwell and Lucas , Hebblewhite and Merrill ). In some partially migratory populations, however, fitness differences can result in reduced prevalence (Middleton et al , Cole et al ) or even loss (Harris et al ) of some behaviors over time. Therefore, when increasing numbers of ungulates exhibit resident behavior, it is not always clear whether prevalence of migratory behavior is also increasing (i.e., the overall population is growing) or whether migratory behavior is declining (i.e., the relative prevalence of resident behavior is increasing).…”