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La Tour du Valat

Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	Are red-backed Shrikes becoming smaller?
Auteurs :	H. Jakober, Auteur ; W. Stauber, Auteur
Type de document :	Article
Dans :	Journal of Ornithology (141(4) OCT 2000)
Article en page(s) :	408-417
Langues:	Anglais
Résumé :	From 1964 to 1998 2811 Red-backed Shrikes were trapped in a stable population near Goppingen (Baden- Wurttemberg, S- Germany, 48 degrees 39'N 09 degrees 47'E). We measured wing length and body mass and plucked an 8th and 9th secondary (s8 and s9), a 2nd greater secondary covert (gc2) and an outer rectrice (t6). During this period the mean wing length decreased in both sexes (Tab. 1, Fig. 1). In females the diminishment began around 1991, in males and full-grown pull. in 1995. Although feather lengths are reduced by abrasion during the breeding season, repeatability in retrapped birds is quite high (Tab. 2). Parent-offspring regression estimates the heritability; its value was high until the end of the 1980s, but has decreased since that time (Fig. 2). For comparison we look the length of pluckd tertials s8 and s9. The length of s8 decreased slightly from 1964 to 1998, while s9 increased. The heritability of the tertials did nor change significantly. Body mass showed no change in this period. Morphological characteristics with a high heritability have no close relation with fitness. Correspondingly, we found no significant connection between the measurements and breeding success or return rate from winter quarters (Tab. 3). The strong decline in the heritability of wing length suggests that environmental variance has increased in recent years.

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