Environmental variability, reliability of information and the timing of migration.

Silke Bauer,Zoltan Barta,John M. McNamara

doi:10.1098/rspb.2020.0622

Abstract

The timing of migration and migratory steps is highly relevant for fitness. Because environmental conditions vary between years, the optimal time for migration varies accordingly. Therefore, migratory animals could clearly benefit from acquiring information as to when it is the best time to migrate in a specific year. Thus, environmental predictability and variability are fundamental characteristics of migration systems but their relationship and consequence for migratory progression has remained unexplored. We develop a simple dynamic model to identify the optimal migration behaviour in environments that differ in predictability, variability and the number of intermediate stop-over sites. Our results indicate that higher predictability along migration routes enables organisms to better time migration when phenology deviates from its long-term average and thus, increases fitness. Information is particularly valuable in highly variable environments and in the final migration-step, i.e. before the destination. Furthermore, we show that a general strategy for obtaining information in relatively uninformative but variable environments is using intermediate stop-over sites that enable migrants to better predict conditions ahead. Our study contributes to a better understanding of the relationship between animal movement and environmental predictability-an important, yet underappreciated factor that strongly influences migratory progression.

Highlights

Migration is an adaptation to conditions that vary seasonally or periodically between favourable, resource-rich and unfavourable or hostile [1]
We develop a simple dynamic model to identify the optimal migration behaviour in environments that differ in predictability, variability and the number of intermediate stop-over sites
Our results indicate that higher predictability along migration routes enables organisms to better time migration when phenology deviates from its long-term average and increases fitness

Summary

Introduction

Migration is an adaptation to conditions that vary seasonally or periodically between favourable, resource-rich and unfavourable or hostile [1]. In which the optimal time occurs invariantly at the same time of the year, natural selection would push organisms to time migration at exactly this best time [4]. We lack a detailed understanding of how animals should schedule migrations under different levels of information about the optimal timing, how the best migration strategy would change in environments differing in variability and which role intermediate stop-over sites could play in modifying these relationships. We address these questions with a simple model that calculates the optimal migration behaviour from a starting (wintering) to a destination (breeding) site

Model description and scenarios

Results

Discussion