Kolonievorming bij Canadese Gans Branta canadensis

On an island of 1.9 ha in a 17m deep gravel pit (21 ha), the number of breeding Canada Geese increased over the past decade (Figure 1). The extend of the increase showed a negative correlation with the severity of the preceding winter (Figure 2), possibly because part of the population skipped breeding after a severe winter. During the early stages of colonisation, the vegetation was short and many nests were depredated, mainly by corvids and possibly by gulls. Over the years the vegetation became taller and more dense, hence offering better protection. Consequently, breeding success improved. Interbreeding was observed between Canada Goose and Barnacle Goose Branta leucopsis, Bar-headed Goose Anser indicus, Ross' Goose Anser rossii and domesticated geese Anser sp.