Variation in movement patterns of mule deer: have we oversimplified migration?

Brock R. McMillan,Madelon van de Kerk,Randy T. Larsen,Daniel D. Olson,Kent R. Hersey

doi:10.1186/s40462-021-00281-7

Abstract

BackgroundConservation and management of migratory animals has gained attention in recent years, but the majority of research has focused on stereotypical ‘migrant’ and ‘resident’ behaviors, often failing to incorporate any atypical behaviors or characterize migratory behaviors beyond distance and timing of the migration. With migration threatened by anthropogenic development and climate change, it is crucial that we understand the full range of migratory behaviors. Our objective was to demonstrate and characterize the variation in migration strategies, including typical and atypical migratory behaviors for mule deer (Odocoileus hemionus) in Utah, USA.MethodsBecause calculation of common metrics such as distance, timing, and use of stopovers during migration did not adequately describe the variation we observed in migratory behavior for this species—particularly when animals visited multiple (> 3) ranges for extended lengths of time—we developed additional methods and categories to describe observed variation in migratory behavior. We first categorized trajectories based on the number of discrete, separate ranges and range shifts between them. Then, we further characterized the variation in migration strategies by examining the timing, duration, and distance traveled within each of the categories. We also examined if and how frequently individual deer switched among categories from year to year.ResultsWe classified 1218 movement trajectories from 722 adult female mule deer, and found that 54.4% were dual-range migrants, who made one round-trip to one distinct range. Multi-range migrants (23.6%) made one round-trip during which they stayed at multiple discrete ranges. Commuters (1.0%) traveled to the same range multiple times, and poly migrants (1.5%) made multiple round-trips to different ranges. Gradual movers (2.5%) did not show a discrete range shift but moved gradually between ranges, whereas residents (12.6%) never left their home ranges, and dispersers (4.4%) left but never returned. Of the deer that we monitored for multiple years, 51.2% switched among categories.ConclusionWe conclude that the substantial number of atypical migratory strategies, as well as the number of deer that switched categories, underlines the importance of studying these less-stereotyped behaviors that may be exhibited by large proportions of populations. Acknowledging and investigating the full complexity and diversity in migratory strategies might uncover unknowns with respect to underlying factors and drivers of migration, and can help shape effective conservation strategies.

Highlights

Conservation and management of migratory animals has gained attention in recent years, but the majority of research has focused on stereotypical ‘migrant’ and ‘resident’ behaviors, often failing to incorporate any atypical behaviors or characterize migratory behaviors beyond distance and timing of the migration
Several authors have claimed that classic examples of typical migratory behavior are probably the exception rather than the rule for many species, and that migration should be viewed as a continuum of behaviors ranging from resident to migrant [9, 10]
With migration threatened by anthropogenic development and climate change, it is crucial that we understand the full range of migratory behaviors [12]

Summary

Introduction

Conservation and management of migratory animals has gained attention in recent years, but the majority of research has focused on stereotypical ‘migrant’ and ‘resident’ behaviors, often failing to incorporate any atypical behaviors or characterize migratory behaviors beyond distance and timing of the migration. Migration of large herbivores has gained attention in recent years, with management strategies aiming to reduce habitat fragmentation and movement barriers in order to maintain corridors between summer and van de Kerk et al Mov Ecol (2021) 9:44 winter ranges [1,2,3]. The majority of migration studies focus only on typical resident or typical migratory behaviors, failing to incorporate any atypical migratory movements [11, 12]. With migration threatened by anthropogenic development and climate change, it is crucial that we understand the full range of migratory behaviors [12]

Objectives

Methods

Results

Discussion

Conclusion