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La Tour du Valat

Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	A method for ageing adult Corncrakes Crex crex
Auteurs :	Rhys E. Green, Auteur ; Norbert Schaffer, Auteur ; Dieter Wend, Auteur
Type de document :	Article
Dans :	Ringing & Migration (20(4) November, 2001)
Article en page(s) :	352-357
Résumé :	The shapes of the tips of Corncrake Crex crex secondary remiges grown by chicks and adults were compared. Measurements of secondaries of birds of known age were obtained from wild Corncrakes in Britain and captive-bred birds originating from Germany and Poland. The tips of secondaries grown in the hatching year were more pointed than those grown in subsequent years in both samples. Secondaries grown in the hatching year are retained until the autumn of the next calendar year. Consequently the average shape of the tips of secondaries of one year old adults was different from that of older birds. The sum of the angles measured at the tips of secondaries 3 to 6 inclusive (numbered ascendantly) was used to quantify this difference. The angle sum scores of known first-years and older birds overlapped, but it is possible to estimate the proportions of the two age classes in a sample of adults of unknown age by assuming that the distribution of scores is the combination of two normal distributions with means and standard deviations taken from the reference samples of known-age birds. The method can also be used to assign individual adults to these two age classes, but if the proportion of errors is kept to less than 1% then it is necessary to leave the 35% of birds which have intermediate scores unaged.

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