Annual Schedule Adjustment by a Long-Distance Migratory Bird

Matching the timing of annual cycle events with the required resources can have crucial consequences for individual fitness. But as the annual cycle is composed of sequential events, a delay at any point may be carried over to the subsequent stage (or more, in a domino effect) and negatively influence individual performance. To investigate how migratory animals navigate their annual schedule and where and when it may be adjusted, we used full annual cycle data on 38 Icelandic whimbrels (Numenius phaeopus islandicus) tracked over 7 years-a subspecies that typically performs long-distance migrations to West Africa. We found that individuals apparently used the wintering sites to compensate for delays that mostly arose as a result of previous successful breeding, and a domino effect was observed from spring departure to laying date, with the potential to affect breeding output. However, the total time saved during all stationary periods is apparently enough to avoid interannual effects between breeding seasons. These findings highlight the importance of preserving good-quality nonbreeding sites in which individuals may adjust annual schedules and avoid potentially adverse effects of arriving late at the breeding grounds.