Aspects of the biology of Egyptian Goose Alopochen aegyptiacus colonizing The Netherlands

Abstract

Since 1967, the Egyptian Goose has established a feral breeding population of some 1350 pairs in the Netherlands and colonized large parts of the country. Aspects of the breeding cycle and the changes in winter numbers are analysed. The Dutch population has a six-month breeding season and overall breeding success in the Netherlands is higher than in Africa, or in the British population. The proportion of successful pairs and overall breeding success decreased a few years after colonization of new areas. Timing of the onset of incubation was positively related to winter severity. Density-dependent factors appeared to begin to operate soon after colonization. As soon as the population stabilized, environmental factors became of major importance. Although population size is reduced during severe winters, the delay in the onset of breeding and relatively high success after such winters, as well as the prolonged breeding season, can quickly compensate for these losses. This combination may explain the relatively greater breeding output of this tropical species in the moderate climate of Western Europe.