Follow the rain? Environmental drivers of Tyrannus flycatcher migration across the New World

MURPHY, M.T.; MACPHERSON, M.; CUETO, V.R.; JAHN, A.E,; TUERO, D.

AUK

AMER ORNITHOLOGISTS UNION

Año: 2018 vol. 153 p. 881 - 894

0004-8038

Predictable seasonal changes in resources are thought to drive the timing of annual animal migrations; however, wecurrently understand little about which environmental cues or resources are tracked by different migratory birdspecies across the planet. Understanding which environmental cues or resources birds track in multiple migratorysystems is a prerequisite to developing generalizable conservation plans for migratory birds in a changing globalenvironment. Within the New World, climatic differences experienced by Nearctic?Neotropical migratory (NNM; i.e.breed in North America and spend the nonbreeding period in the Neotropics) and Neotropical austral migratory (NAM;i.e. breed and spend the nonbreeding period wholly within South America) bird species suggest that their migratorystrategies may be shaped by unique selective pressures. We used data gathered from individuals fitted with light-levelgeolocators to build species distribution models (SDMs) to test which environmental factors drive the migratorystrategies of species in each system. To do so, we evaluated whether temperature, precipitation, and primaryproductivity (NDVI) were related to the seasonal distributions of an NNM (Eastern Kingbird [Tyrannus tyrannus]) andNAM species (Fork-tailed Flycatcher [T. savana]). Both Eastern Kingbird and Fork-tailed Flycatcher locations werepositively correlated with high precipitation during their nonbreeding seasons. Eastern Kingbird locations werepositively correlated with both NDVI and temperature during their breeding season and both pre- and post-breedingmigrations. Fork-tailed Flycatcher locations were positively correlated with both temperature and precipitation duringboth migrations, but only temperature during the breeding season. The value of extending the application ofgeolocator data, such as in SDMs, is underscored by the finding that precipitation was such an important predictor ofthe nonbreeding distributions of both types of migrants, as it remains unclear how global climate change will affectwet?dry cycles in the tropics.