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Ecological Causes and Consequences of Intratropical Migration in Temperate-breeding Migratory Birds
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New discoveries from direct tracking of temperate-breeding passerines show that
intra-tropical migration (ITM) is common in a growing number of species which has important
implications for understanding their evolution of migration, population dynamics, and
conservation needs. Our large sample size (N = 191) for Purple Martins Progne subis subis tracked
with geolocators to winter sites in Brazil, combined with geolocator deployments at breeding
colonies across North America, allowed us to test hypotheses for ITM which has not yet been
possible to do for other species. ITM in Purple Martins was not obligate; only 44% of individuals
exhibited ITM and movements were not coordinated in time or space. We found no evidence to
support the resource hypothesis; rainfall, and temperature experienced by individual birds
during their last 2 weeks at their first roost site were similar to conditions at their second roost
site after ITM. Birds generally migrated away from the heavily forested northwestern Amazon to
less forested regions to the south and east. ITM in this aerial insectivore appears to support the
competition avoidance hypothesis and may be triggered by increasing local density in the core
wintering region. Full-life cycle models and migratory networks will have to incorporate ITM to
properly address seasonal carry over effects and to identify which wintering regions are most
important for conservation. -
- Date created
- 2016-01-01
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- Subjects / Keywords
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- Type of Item
- Article (Draft / Submitted)