Brent geese in a meta-ecosystem: The ecology of migratory species at different scales

Migratory species are at risk in todays’ changing world, because of their dependence on different areas during specific periods of the year. Therefore, it is important to understand the ecology of these species, at large scales: along the total migratory route, and at small scales: the interactions with e.g. food. In this thesis the ecology of the brent goose is studied at different spatial scales. First, underlying reasons for migratory behavior are considered, leading to the conclusion that differences in requirements of adults and young can form an important explanation for migration in many species. Next, the habitat use of the brent goose is studied both at the flyway scale as locally, in the Wadden Sea, using novel network techniques. These techniques allowed to statistically show that movement patterns along the flyway differed depending on the type of habitat. Furthermore, locally, brent geese which use agricultural pasture in the Wadden Sea area use patches for shorter periods, because of human disturbance, and use more patches, because of the homogeneous availability of high quality food, compared to birds which use natural salt marshes that show a heterogeneous availability of food and form the original habitat of brent geese in spring. Finally the interactions of brent geese with their food on salt marshes was studied, showing that brent geese prefer plants high sugar contents. High sugar richness is an adaptation to high salinity. With high salt contents the same adaptation is achieved, but plants with this strategy are avoided by brent geese.