Moult and ageing of storm petrels hydrobates pelagicus

Abstract

Current published ageing criteria for Storm Petrels, Hydrobates pelagicus appear to be unreliable, so fledged birds are not aged to a high degree of accuracy, restricting the scope of age-specific studies. Analyses of moult and feather wear were carried out on 28 specimens of Storm Petrels which were washed ashore on the southern coast of Portugal during January 1996, and on a further 780 live individuals which were trapped during May-July 1998, also on the southern coast of Portugal. Differences in the pattern of wear and bleaching of the primary feathers between those grown simultaneously in the nest and those grown sequentially over a long period by older birds, allows fledged individuals to be aged as in their first year, or older. Using primary wear to age individuals, the shape of the outermost long primary feather can then also be shown to be a reliable ageing criterion. Some birds in active primary moult can be aged even more specifically by a combination of primary wear and the shape of the outermost primary.