Tracking through Life Stages: Adult, Immature and Juvenile Autumn Migration in a Long-Lived Seabird

Clara Péron,David Grémillet,Katherine Renton

doi:10.1371/journal.pone.0072713

Abstract

Seasonal long-distance migration is likely to be experienced in a contrasted manner by juvenile, immature and adult birds, leading to variations in migratory routes, timing and behaviour. We provide the first analysis of late summer movements and autumn migration in these three life stages, which were tracked concurrently using satellite tags, geolocators or GPS recorders in a long-ranging migratory seabird, the Scopoli’s shearwater (formerly named Cory’s shearwater, Calonectris diomedea ) breeding on two French Mediterranean islands. During the late breeding season, immatures foraged around their colony like breeding adults, but they were the only group showing potential prospecting movements around non-natal colonies. Global migration routes were broadly comparable between the two populations and the three life stages, with all individuals heading towards the Atlantic Ocean through the strait of Gibraltar and travelling along the West African coast, up to 8000 km from their colony. However, detailed comparison of timing, trajectory and oceanographic conditions experienced by the birds revealed remarkable age-related differences. Compared to adults and immatures, juveniles made a longer stop-over in the Balearic Sea (10 days vs 4 days in average), showed lower synchrony in crossing the Gibraltar strait, had more sinuous pathways and covered longer daily distances (240 km.d-1 vs 170 km.d-1). Analysis of oceanographic habitats along migratory routes revealed funnelling selection of habitat towards coastal and more productive waters with increasing age. Younger birds may have reduced navigational ability and learn progressively fine-scale migration routes towards the more profitable travelling and wintering areas. Our study demonstrates the importance of tracking long-lived species through the stages, to better understand migratory behavior and assess differential exposure to at-sea threats. Shared distribution between life stages and populations make Scopoli’s shearwaters particularly vulnerable to extreme mortality events in autumn and winter. Such knowledge is key for the conservation of critical marine habitats.

Highlights

Autumn migration from high latitudes is triggered by decreasing temperatures, food shortage and day length shortening
Studying movements of individuals belonging to early life stages using electronic devices is yet challenging because they are difficult to access before their first breeding attempt and often experience higher mortality than adults [15,23,24,25]
Immature and adult birds did differ in their autumn migratory paths, timing and behavior and the different age groups studied showed different oceanographic preferences along their migration paths

Summary

Introduction

Autumn migration from high latitudes is triggered by decreasing temperatures, food shortage and day length shortening. Since the advent of miniaturized long-lasting electronic tracking devices, many studies have explored the migratory pathways of both terrestrial [5,6,7] and marine species [8,9,10,11], revealing extraordinary long-distance trans-equatorial migrations [12,13,14]. Most of these studies have been conducted on adults for methodological reasons [15]. Conservation measures are currently essentially based on adult distribution during the breeding and/or inter-breeding season [28], spatial distribution of the other life stages can differ significantly [18,29]

Methods

Results

Conclusion