Data from: The cost of migration: spoonbills suffer higher mortality during longer spring migrations

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 have investigated whether mortality during the actual migration increases with migration distance. Here we compared seasonal survival between Eurasian spoonbills that breed in The Netherlands and migrate different distances (c. 1,000 km, 2,000 km and 4,500 km) to winter in France, Iberia or Mauritania. 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 to 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 longer migrations.