Abstract
Explanations for the wide variety of seasonal migration patterns of animals all carry the assumption that migration is costly and that this cost increases with migration distance. Although in some studies, the relationships between migration distance and breeding success or annual survival are established, none has investigated whether mortality during the actual migration increases with migration distance. Here, we compared seasonal survival between Eurasian spoonbills (Platalea leucorodia leucorodia) that breed in The Netherlands and migrate different distances (ca 1000, 2000 and 4500 km) to winter in France, Iberia and Mauritania, respectively. On the basis of resightings of individually marked birds throughout the year between 2005 and 2012, we show that summer, autumn and winter survival were very high and independent of migration distance, whereas mortality during spring migration was much higher (18%) for the birds that wintered in Mauritania, compared with those flying only as far as France (5%) or Iberia (6%). As such, this study is the first to show empirical evidence for increased mortality during some long migrations, likely driven by the presence of a physical barrier (the Sahara desert) in combination with suboptimal fuelling and unfavourable weather conditions en route.
Highlights
Migration—the regular seasonal movement of individuals, often from a breeding location to a non-breeding location and back—is a common and taxonomically widespread phenomenon throughout the animal kingdom [1]
There was a strong effect of migration strategy on spring migration survival (tPhe sum of Akaike weights of models including the effect 1⁄4 1.00, table 1), with birds wintering in Mauritania being three times more likely to die during spring migration (17.7%) than birds wintering in France (5.1%) or Iberia (5.6%)
The main result of this study is that mortality during spring migration was higher in the longest distance migrating spoonbills that wintered in Mauritania, compared with those staying in Europe
Summary
Migration—the regular seasonal movement of individuals, often from a breeding location to a non-breeding location and back—is a common and taxonomically widespread phenomenon throughout the animal kingdom [1]. Migration is considered to have evolved as an adaptation to exploit seasonal peaks in resource abundance while avoiding seasonal resource depression during the non-breeding period by travelling—at some cost—to more benign areas. As reviewed in [4], many theories have been developed to explain this enormous variation in migration patterns. These theories all assume that migration is costly and that this cost increases with migration distance. This cost may be direct, causing reduced survival during migration [5,6], or it may carry over to the season, reducing subsequent survival or reproductive output
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