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Ecological Causes and Consequences of Intratropical Migration in Temperate-breeding Migratory Birds

  • Author(s) / Creator(s)
  • 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.

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  • Type of Item
    Article (Draft / Submitted)
  • DOI
  • License
    Attribution-NonCommercial 4.0 International
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  • Citation for previous publication
    • Stutchbury, B. J. M., Siddiqui, R., Applegate, K., Hvenegaard, G. T., Mammenga, P., Mickle, N., Pearman, M., Ray, J. D., Savage, A., Shaheen, T., Fraser, K. C., & Zuk, M. (2016). Ecological Causes and Consequences of Intratropical Migration in Temperate-Breeding Migratory Birds. American Naturalist, 188, S28–S40.