Effects of post-breeding moult and energetic condition on timing of songbird migration into the tropics |
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Authors: | Bridget J. M. Stutchbury Elizabeth A. Gow Tyler Done Maggie MacPherson James W. Fox Vsevolod Afanasyev |
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Affiliation: | 1.Department of Biology, York University, Toronto, Ontario, Canada, M3J 1P3;2.British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 0ET, UK |
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Abstract: | Each autumn billions of songbirds migrate between the temperate zone and tropics, but little is known about how events on the breeding grounds affect migration to the tropics. Here, we use light level geolocators to track the autumn migration of wood thrushes Hylocichla mustelina and test for the first time if late moult and poor physiological condition prior to migration delays arrival on the winter territory. Late nesting thrushes postponed feather moult, and birds with less advanced moult in August were significantly farther north on 10 October while en route to the tropics. Individuals in relatively poor energetic condition in August (high β-Hydroxybutyrate, low triglyceride, narrow feather growth bars) passed into the tropics significantly later in October. However, late moult and poor pre-migratory condition did not result in late arrival on the winter territory because stopover duration was highly variable late in migration. Although carry-over effects from the winter territory to spring migration may be strong in migratory songbirds, our study suggests that high reproductive effort late in the season does not impose time constraints that delay winter territory acquisition. |
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Keywords: | migration geolocator neotropical migrant plasma metabolite moult |
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