The East Atlantic flyway population of pale-bellied Brent Geese Branta hrota is, with its current population estimate of 6000 birds, one of the smallest goose populations of the World. During 1991-99 a total of 361 individually marked Brent Geese have been marked and followed in their wintering areas by intensive field studies. In this paper we use standard capture-recapture analysis to investigate seasonal and annual survival rates of the population. We divided the year into three periods with different spatial distribution of the geese, autumn (September-December), winter (Jan-March), and spring (April-May), and estimated survival rates between these periods. Survival from autumn to winter was high (0.999 monthly survival rate (MSR)), lower from winter to spring (average 0.985 MSR; 0.991 MSR in years with 'normal' temperatures, 0.968 MSR during a severe winter, 1995/96), and lowest from spring to autumn (0.982 MSR), -resulting in an overall annual survival rate of 0.870. We discuss the variation in seasonal and annual mortality rates in relation to constraints faced by the birds such as seasonal changes in availability of food resources, severe winters, long-distance migration and predation risk.
Ardea, 2001, Vol 89, Issue special issue, p. 101-112
branta hrota; survival; mark-recapture; severe winters