Wednesday 29 December 2010

Ageing geese

No, not that they are getting older but the term used for discovering how many young birds there are in the flocks, something I do every autumn and early winter. Breeding success varies considerably from year to year, because of adverse weather on the breeding grounds at critical times, like the hatch, or because the birds fail to get into good enough condition in the spring.
The percentage of young birds is important information to gather, but in order to do so it is necessary to distinguish between adults and young. In the Whitefronts, that is comparatively easy as the young birds lack the black belly bars of the adults while the white forehead is absent or smaller. In Barnacles, the differences are more subtle, with the adults having clear black and white feather edgings on their wings, while on the young they are browner and more 'messy'. As in all geese and swans, the birds stay in family parties throughout the winter, which means one can gather information not just on the percentage of young, but also the average size of broods.
2010 was a very good breeding season for the Whitefronts, with just over 20% young, while the Barnacles did slightly better than average, with c.11%.
A Barnacle Goose family. The male parent spends more time looking for danger than the female, who is following him, while the young bird brings up the rear

A Whitefront family. Three young are on the left. The male parent is alert, the female feeds.

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