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La Tour du Valat

Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	Phenology, sex ratios, and population trends of Selasphorus hummingbirds in central coastal California
Auteurs :	S. N. G. Howell, Auteur ; T. Gardali, Auteur
Type de document :	Article
Dans :	Journal of Field Ornithology (74(1) WIN 2003)
Article en page(s) :	17-25
Langues:	Anglais
Résumé :	From 1980 to 2000, we mist-netted 2412 Allen's Hummingbirds (Selasphorus sasin) and 203 Rufous Hummingbirds (S. rufus) at a site in central coastal California. Adult Allen's occurred from late January to early August and juveniles from early April to early September. Overall ratios of female to male Allen's were 2.5:1 for adults, 1:1.1 for juveniles. The breeding season female-to-male ratio for adult Allen's of 6.2:1 probably reflected net placement at riparian edges between nests and feeding areas for females. Adult Rufous occurred as transients from mid-February to early May and late June to mid-August and juveniles from mid June to late September. Overall ratios of female to male Rufous were 2.3:1 for adults in spring, 1:1.1 for juveniles. For adults, there was little evidence for a spring migration peak in Allen's, but a fall migration peak was marked. In contrast, adult Rufous showed a spring migration peak but were rare in fall. The two species' main southbound routes in California (coastal for Allen's, interior for Rufous) may, in combination with temporal separation, help partition nectar resources. Capture rates for both age groups of Allen's Hummingbirds indicated a stable population. Juvenile Rufous showed a significant decline in capture rates, reasons for which are unknown.

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