Sex-specific differences in spring and autumn migration in a northern large herbivore

Lucie Debeffe,Atle Mysterud,Inger Maren Rivrud,Erling L Meisingset

doi:10.1038/s41598-019-42639-3

Abstract

Ongoing global warming is now affecting migratory cycles in a large variety of taxa in seasonally variable environments. Disruption of migratory systems can cause population decline and affect ecosystem function across the globe. It is therefore urgent to understand the drivers of migration and how the different fitness limitations of the sexes affect migration, but studies seldom considered the full annual cycle. We analysed the annual migration cycle of 237 red deer (Cervus elaphus) in Norway and investigate how different seasonal limitations affected the variation in a suite of migration characteristics. We found fundamental differences in migration phenology between seasons, and migratory traits were much more variable in males. Spring migratory movements were characterized by longer distance roamed, lower speed, lasted longer, more frequent use of stopovers, timing was more synchronized and coincided with onset of plant growth, and with higher daily activity levels. Timing of autumn migration was more variable and not closely related to cease of plant growth. Our study emphasizes the benefits of studying the full annual cycle to gain further insight into the migration process, and how understanding the limitations of the full annual migration process of both sexes is critical for conservation purposes.

Highlights

Migration between distinct seasonal ranges is widespread and commonly observed in taxa as different as invertebrates, fishes, birds and mammals[1]
In chamois (Rupicapra rupicapra), it was recently demonstrated that onset of autumn shaped the timing of births more than onset of spring[19], and mule deer (Odocoileus hemionus) overwinter survival was driven by both spring and autumn plant phenology[20]
The rutting season overlaps with the autumn migration season in many species, and onset of male migration in autumn is less linked to environmental stimuli compared to female autumn migration in red deer (Cervus elaphus)[24]

Summary

Introduction

Migration between distinct seasonal ranges is widespread and commonly observed in taxa as different as invertebrates, fishes, birds and mammals[1]. From the body size and gastrocentric hypothesis, the larger males can survive on lower quality diet and not be expected to follow the green wave close These hypotheses predict sexual differences in migration speed and duration, and in use of stopover sites (i.e. places where migratory individuals stop during the migration and before continuing their journey). Plant phenology drives spring migratory behaviour in red deer, while onset of hunting is an important trigger of autumn migration[11,24] In such context, we investigate how different seasonal and sex-specific limitations affected the variation in a suite of migration characteristics at the scale of the migration event (timing of departure, total distance roamed, duration of migration, movement speed, use of stopover sites) and using data on daily activity patterns. If rut determine male autumn movements, with males following females as a ‘resource’, we predict migration timing to be less variable for males than females, and to be quicker in autumn compared to spring, with a more direct route (i.e. a lower total distance roamed), a higher travel speed and a lower probability of using stopover sites (especially when departure is late)

Methods

Results

Conclusion