SEEN - SE European Bird Migration Network
Does inter-specific competition determine migration strategy of the Willow Warbler Phylloscopus trochilus and Chiffchaff Phylloscopus collybita?
M. Ciach 1,2
1Department of Nature-Cultural Heritage, Animal Ecology and Wildlife Management, University of Agriculture, Kraków, Poland
2 Bird Migration Research Station, University of GdaƄsk, Przebendowo, 84-210 Choczewo, Poland

The Willow Warbler Phylloscopus trochilus and Chiffchaff Phylloscopus collybita are closely related species, exhibiting similarities in their morphological and ecological requirements. Long term data from bird ringing stations and direct observation of migrants showed that inter-specific relations might influence migration strategy. Migration dynamics of both species were closely connected – the beginning of the Chiffchaff migration depended on the end of the Willow Warbler migration. Relation between both species migration was confirmed by direct observation of habitat use and preferences in stopover site. While the Willow Warbler used optimal habitats exclusively (thin branches with leaves), the Chiffchaff showed shift in habitat use during migration. In first period of autumn migration, the Chiffchaff used sub-optimal and marginal habitats (thick and leafless branches). When the Willow Warbler left stopover sites, the Chiffchaff started to use optimal habitats, previously occupied by the competitor. A suggested model of reciprocal-dependent migration explains the migration strategy of closely related species. Inter- and intra-specific competition could play a significant role in the evolution of migration strategies.
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