Carryover effects of long-distance avian migration are weaker than effects of breeding environment in a partially migratory bird

Claire Buchan,Juan Miguel González,James J Gilroy,Aldina M A Franco,Javier Bustamante,Alina D Marca,Philip W Atkinson,Inês Catry

doi:10.1038/s41598-020-80341-x

Abstract

Migration may expose individuals to a wide range of increasing anthropogenic threats. In addition to direct mortality effects, this exposure may influence post-migratory reproductive fitness. Partial migration—where a population comprises migrants and residents—represents a powerful opportunity to explore carryover effects of migration. Studies of partial migration in birds typically examine short-distance systems; here we studied an unusual system where residents breed in mixed colonies alongside long-distance trans-Saharan migrants (lesser kestrels (Falco naumanni) in Spain). Combining geolocator data, stable isotope analysis and resighting data, we examined the effects of this stark difference in migratory strategy on body condition, breeding phenology and breeding success. We monitored four colonies in two regions of southern Spain for five consecutive years (2014–2018), yielding 1962 captures, determining migratory strategy for 141 adult bird-years. Despite a 3000-km difference in distance travelled, we find no effect of strategy on breeding parameters. We find weak evidence for a short-term negative carryover effect of migration on body condition, but this was only apparent in the breeding region with lower primary productivity. Our results indicate that carryover effects of even highly divergent migratory strategies may be minimal relative to effects of conditions experienced on breeding grounds.

Highlights

Migration may expose individuals to a wide range of increasing anthropogenic threats
We examine carryover effects in an unusual example of long-distance partial migration, where non-migratory individuals are fully resident in the Spanish breeding grounds throughout the year, while migrants undertake a c. 3000-km trans-Saharan migration, such that individuals may be exposed to very different costs between the two strategies
Of 25 adult individuals (59 bird-years) for which we determined migratory strategy in multiple years (17 individuals for two years, seven for three years and one for four years), 21 maintained a consistent migratory strategy, three individuals switched from migrants to residents, and one individual switched from being a resident to being a migrant

Summary

Introduction

Migration may expose individuals to a wide range of increasing anthropogenic threats. Environmental conditions during spring migration can influence arrival time and body condition at the breeding grounds, with consequences for subsequent breeding success. Distances and timings can vary significantly within p opulations[10], sometimes leading to significant variation in survival[11] Such differences may apply to non-lethal carryover effects; larger migratory distances have been linked to later arrival on breeding g rounds[12] and lower breeding s uccess[13]. Partial migration, where migrant and non-migrant individuals exist within the same p opulation[14,15], provides a powerful natural experiment to explore these carryover effects, by comparing fitness parameters of migrants and residents[16]. We may expect to see differences in carryover effects between migrants and residents across different fitness components

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Discussion

Conclusion