PhD ceremony Ms. T. Lok: Spoonbills as a model system. A demographic cost-benefit analysis of differential migration
|Fr 15-11-2013 at 11:00
PhD ceremony: Ms. T. Lok, 11.00 uur, Academiegebouw, Broerstraat 5, Groningen
Dissertation: Spoonbills as a model system. A demographic cost-benefit analysis of differential migration
Promotor(s): prof. T. Piersma, prof. J.M. Tinbergen
Faculty: Mathematics and Natural Sciences
Migration, the seasonal movement between breeding and non-breeding areas, is a widespread phenomenon in the animal kingdom. Yet there is considerable variation in the extent to which animals migrate. Some don’t migrate at all, whereas others transverse the entire globe each year. The aim of the thesis of Tamar Lok was to get a better understanding of the evolutionary drivers of this variation, by quantifying the costs and benefits of migration, and how these are influenced by density dependence (competition). Using 25 years of resightings of individually colour-banded spoonbills born in The Netherlands, Lok found consistent individual variation in how far birds migrate and where they spend the winter, ranging from France to Senegal. During this period, the population grew from 400 to 2500 breeding pairs, accompanied by a decrease in annual survival of spoonbills of all ages. Survival of adult birds, that perform annual migration, decreased only between mid winter and arrival at the breeding grounds. Although the rate of decrease was independent of an individual’s migration strategy, survival was consistently lower for the birds wintering in Mauritania or Senegal, which was mainly caused by higher mortality during spring migration. Despite their lower survival, and also somewhat lower breeding success, most birds originally wintered in Mauritania or Senegal, though more and more birds now start wintering in Europe. Therefore, rather than density dependence causing more birds to winter in poorer quality areas, “traditional” long-distance migration appears to constrain spoonbills to adapt sufficiently fast to changing conditions along a flyway.
Read also the press release: Spoonbills habitually fly further than is good for them