Temperature-based models of the migration of Swainson's Flycatcher (Myiarchus swainsoni) across South America: A new use for museum specimens of migratory birds

The vastly disjunct distributions of long-distance migratory animals pose c hallenges to the modeling of species distributions and, for species with po orly known migratory routes and destinations, to the definition of migratio n patterns. We have addressed these issues with a method that predicts geog raphical ranges of migratory birds month-by-month. The method generates pre dictive models of distribution based on temperature and localities and date s of museum specimens. A model is first developed using specimen data from any one month. That model is then applied under the temperature conditions of a second month to predict the range of the migrant in the second month. In effect, description of the migration pattern is addressed quantitatively in terms of the magnitude of the departure shown by the migrant from a con stant response to temperature. We demonstrate the method with a South Ameri can migratory bird, Swainson's Flycatcher Myiarchus swainsoni. Models gener ated from the months of migratory passage April and September generally are better predictors of either the breeding or the non-breeding ranges than m odels generated from other months of the year.