Evol Ecol Res 11: 413-420 (2009)     Full PDF if your library subscribes.

The morphology, flight, and flocking behaviour of migrating raptors

Robert W. Black and Alyssa Borowske

Department of Biology, Cornell College, Mount Vernon, Iowa, USA

Correspondence: R.W. Black, Department of Biology, Cornell College, 600 First Street West, Mount Vernon, IA 52314, USA.
e-mail: bblack@cornellcollege.edu


Question: Is there a clear relationship between the morphology of raptors, their styles of flight, and flocking behaviour during autumn migration?

Methods: We documented the autumn migration and flocking behaviour of raptors at the Macbride Raptor Migration Research Station in Johnson County, Iowa between 1992 and 2003. We then compared the flocking behaviour of raptors of different species and flight styles. We also compared our results with the predictions of common hypotheses on the evolution of flocking behaviour in birds.

Conclusions: Raptors of different species and styles of flight exhibit both unique tendencies to flock and different flock sizes during autumn migration. Raptors that utilize primarily powered flight (falcons, harriers, and accipiters) are less likely to flock and exhibit a smaller flock size than do soaring raptors (buteos and eagles). The ‘thermal location and utilization’ hypothesis is the only hypothesis on the evolution of flocking behaviour that is generally applicable to the migration of raptors at this mid-western site.

Keywords: autumn migration, flight style, flocking behaviour, morphology, raptor.

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