In order to manage populations of migratory geese a better understanding of the mechanisms that determine the size of these populations is needed. The objective of this project is to investigate such mechanisms, within the framework of the entire population of Dark-bellied Brent Geese, that winters in western Europe, and breeds in northern Siberia. The final objective of this project is to help predict future numbers of geese that will winter in western Europe in order to be able to forecast levels of agricultural damage caused by geese. Though hunting is an important factor determining the size of most goose populations, this is not a focal point in this project. Therefore this project focuses on a virtually non-hunted subspecies, viz. the Dark-bellied Brent Goose. Research activities Field work has been carried out in the Pyasina-delta in northern Taymyr, Russia during six consecutive summers from 1990 - 1995 in order to cover two complete lemming cycles. The project focuses the one hand on natural predators (like arctic foxes, Snowy Owls, Glaucous Gulls and Herring Gulls, and even Polar Bears) as a regulatory mechanism for the Dark-bellied Brent Geese, a virtually non-hunted subspecies. Lemming cycles have an important effect on the abundance and behaviour of most of these predators, and measuring lemming density forms an integral part of this study. On the other hand weather conditions, as well as the body condition of the geese themselves are being studied, because those factors are in themselves extremely important predictors of breeding success.