Surfing the Heat Wave or the Green Wave: Divergent Ecological and Evolutionary Consequences for Nearctic Neotropical and Austral Migrant Kingbirds

JAHN, A.E,; TUERO, D.; MACPHERSON, M.; ROEDER, D.; HUSAK, M.S.; ETESSAM, E.; CEREGHETTI, J.; CUETO, V.R.; HENDRIX, T.; SARASOLA, J.H.; LISTER, C.

D. Roeder, C. Lister, T. Hendrix & A. E?Etessam

Congreso; VI North American Ornithological Conference; 2016

American Ornithological Society

Geolocationstudies over the last five years have revealed that a surprising number ofmigrant passerine species of the Americas practice winter itinerancy. Winteritinerancy ? moving from place to place across the winter season ? is mostknown in the Palearctic insectivorous bird migration system and has been linkedto the wet and dry seasons in African savannahs. One explanation of this typeof frequent movement has been termed ?the Green Wave hypothesis?, and has beenshown in geese that follow a seasonal wave of new plant growth throughout theirannual cycle. South America likewise has savannahs north and south of theequator that experience wet and dry seasons. However, due to its narrow shape,and position over the equator, South America has low seasonal variation inprimary production (growing plants), and has high between year variability inprimary productivity due to El Niño cycles. So why do birds migrate there? Astudy by Renfrew et al. (2013) showed Bobolinks tracking Normalized DifferenceVegetation Index (NDVI) during their winter movements between grasslands withinSouth America. Using Ripley?s K function present evidence that food limitation(energy-selected migration) is a stronger selection pressure for Australmigrants (Fork-tailed Flycatcher, Tropical Kingbird) in comparison to thetime-limited strategies of Nearctic-Neotropical migrants (Eastern & WesternKingbird, Scissor-tailed Flycatcher). Austral migrants clustered around NDVIwhen molting (tracking emergence of food), while Nearctic Neotropical migrantsclustered around high temperatures year round. Future research should focus onthe influence of changing climate on these two divergent migration strategies.