Regulation of numbers of Dark-bellied Brent Geese Branta bernicla bernicla on spring staging sites.

The usage of the Boschplaat salt-marsh on Terschelling over a 30-year period by Brent Geese Branta b. bernicla, is compared with that on improved grassland on Texel. Natural salt-marsh turns out to be a preferred spring staging habitat. Spring feeding on grassland is a new phenomenon. An exponential model shows that, with the increase in world population size of this subspecies, on the salt-marsh an asymptotic value in numbers has been reached, while on the grassland site further growth is still to be expected. Bird censuses, data on the proportion of first-winter birds, survival estimates from colour-ringed birds, and re-sightings of individuals, have been used to predict the number to return to the same spring staging site next year. The return rate of marked birds in relation to spring body-mass has been compared for both study sites. Re-sightings of marked individuals show that site-tenacity is high. However, there are clear differences between the Boschplaat salt-marsh and the Texel grassland site. In springs following a good breeding season world population size has increased markedly, and competition on the salt-marsh is high. Particularly males with lower body-mass are less likely to return to the same salt-marsh in a subsequent spring.

Ebbinge B.S., ARDEA 80 (2): 203-228