Ardea
Official journal of the Netherlands Ornithologists' Union

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Patterson I.J. & Hearn R.D. (2006) Month to month changes in age ratio and brood size in Pink-footed Geese Anser brachyrhynchus in autumn. ARDEA 94 (2): 175-183
The conservation and management of wild goose populations requires an accurate estimate of productivity to be made each year, usually soon after the birdsí arrival in the wintering grounds. The best time to make the estimates is not always clear, however, since the measures used may vary over the autumn. Seasonal variation in the percentage of juveniles and in mean brood size in Pink-footed Geese Anser brachyrhynchus were investigated, both in the UK as a whole and at one specific site. Data from 1994 to 2002, held by The Wildfowl & Wetlands Trust (WWT), were used to investigate national trends, while data from the Loch of Strathbeg, Aberdeenshire were used to test for variation at one site. A significant decrease from September to November in the percentage of juveniles in the population was found in both sets of data. Both sets of data also showed a significant decrease in mean brood size from September to November. The percentage decrease in brood size (9%) was less than that in the proportion of juveniles in the population (41%). There was no correlation between the two measures in any month or between their month to month changes. It is suggested that only about a quarter of the decrease in the percentage of juveniles from September to November can be accounted for by differential shooting mortality of juveniles and that later arrival of sections of the population with fewer young might be involved.


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