In this issue, two studies examine the extent to which variation in migratory behaviour influences individual fitness across a population. Lok, Veldhoen, Overdijk, Tinbergen, and Piersma (2017) examine reproductive success and post-fledging survival in a population of Eurasian spoonbills (Platalea leucorodia), comparing individuals that winter in south-west Europe against those migrating to sub-Saharan Africa, while Grist et al. (2017) measure reproductive success in a population of European shags (Phalacrocorax aristotelis) breeding in Scotland that either remain resident or migrate to surrounding waters. Both studies find that individuals migrating longer distances tend to show later initiation of breeding attempts. In turn, longer migration correlates with lower reproductive success in both populations. In spoonbills, this effect is most pronounced in older male birds, while young individuals show little difference in breeding success with respect to migration distance. In shags, fitness benefits of residence were most pronounced when both individuals of a pair were resident, although there was no evidence of assortative mating. Both studies provide fascinating new insights into the role migratory variability can play in shaping population dynamics.
- partial migration
- climate change