Spatial demography of black-tailed godwits: Metapopulation dynamics in a fragmented agricultural landscape

How is it possible that such an iconic species as the black-tailed godwit, which has been studied for decades and plays an important role in Dutch nature conservation, is still a topic of concern? The main reason of its decline is the intensification of agricultural land use. In this thesis we studied the population dynamics of black-tailed godwits, to better understand the underlying reasons. On the basis of a thorough demographic field study, we estimated the annual survival rate of young and adult godwits, where they started to breed and with whom, and if their eggs hatched successfully. With this information we could estimate whether reproduction was high enough to compensate mortality of adult godwits. We compared populations breeding on herb-rich wet meadows, often especially managed for meadow birds, with populations breeding on modern grassland monocultures of intensified agriculture. On herb-rich meadows, reproduction was often just enough to compensate for mortality, which means that the population breeding here was a “source”. The reproduction of populations breeding on grassland monocultures was often too low, and the population was a “sink”. Yet, the population breeding on meadows could not grow, as too many young dispersed to sinks. What could we do to safeguard the future of godwits? The most effective measure is to increase chick survival. Most herb-rich meadows were mown on 15 June, when 40% of the chicks have not fledged. Postponing mowing until after chicks have fledged, would already result in a population growth.