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Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	A source population of Black Redstarts (Phoenicurus ochruros) in villages with a high density of feral cats (Felis catus)
Auteurs :	M. Weggler, Auteur ; B. Leu, Auteur
Type de document :	Article
Dans :	Journal of Ornithology (142(3) JUL 2001)
Article en page(s) :	273-283
Langues:	Anglais
Résumé :	Between March 1994 and April 1997 we determined the source-sink status of a population of Black Redstarts (Phoenicurus ochruros) in two adjacent mountain villages in Switzerland, and estimated mortality attributable to feral cats (Felis catus). The finite rate of increase of the population was 1.06 +/- 0.09 (lambda +/- s. e.). Hence, during the three study years the local population had a source status (lambda >1). The ratio between the number of produced (103) and absorbed breeders (88) - another way to evaluate source-sink status - revealed a rate of increase of 1.17. In total, 307 young fledged during the study period. Survival rate between fledging and the next breeding season was estimated to be 0.336, so 103 new breeders were produced out of the 307 fledglings. This number is slightly higher than the 94 breeders the population lost through mortality. The finite rate of increase of the population without the observed losses from cat predation would be lambda = 1.20, assuming that this would not affect fecundity and mortality from other sources. Therefore, predation by cats reduced the productivity of this population by at least 12% (from 1.20 to 1.06) but did not convert it into a sink population. A comparison of the mortality of eggs, nestlings and juveniles, in combination with direct observations, suggested that juveniles were most vulnerable to cat predation between fledging and their independence after eight days. Predation by cats caused 33% of egg fatalities, 20 % of nestling fatalities, greater than or equal to 10 % of fledgling fatalities and greater than or equal to 3% of adult fatalities.

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