Ebbinge B.S. (1992) Regulation of numbers of Dark-bellied Brent Geese Branta bernicla bernicla on spring staging sites. ARDEA 80 (2): 203-228

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. On the grassland site males are equally likely to return, irrespective their body-mass. In years following poor breeding this difference is not noticeable. Then, there is immigration of new birds to the Boschplaat salt-marshes, while from Texel some emigration takes place. In late May males predominate on the grassland site, whereas the reverse is the case on the salt-marsh. In females survival is lower in the lightest category, but no differences in the rate of return between the two spring feeding habitats were apparent. Young birds spending their first spring on the grassland site are more likely to return, whereas those on the salt-marsh are seen more often elsewhere. This suggests that the salt-marsh area is filled to capacity in spring, making it hard for young birds to settle. The carrying capacity of salt-marsh in spring has been estimated by dividing the mean peak number of geese by the total suitable grazing area.