The proximate and ultimate causes of flocking in migratory raptors have received little attention to date and thus are not well understood. In order for flocking behavior to have evolved in a particular species, flocking must somehow enhance the survival and reproductive success of the individuals of that species.
Migratory raptors that are considered “regular flockers” (less than 15 % of all migratory raptor species) have been described to generally have the following four traits in common: 1. they migrate long distances, 2. they are primarily insectivorous during migration, 3. all individuals within each species have similar migration destinations and 4. each species contains many individuals. I propose that, in addition to the above characteristics, the flocking behavior of migratory raptors is related to the wing shape and flight patterns typical of particular species. Specifically, I propose that some raptors form flocks so that they may make optimal use of thermals; rising warm air provides lift to migrants and allows birds to save energy by reducing the need to flap during flight.
My data supports the hypothesis that those raptor species that have evolved flight patterns dominated by soaring are likely to take advantage of thermals and are the most likely species to form flocks during migration. Conversely, raptor species that exhibit primarily flapping flight during migration are not likely to form flocks.
Alyssa Borowske, ’07 Barre, VT
Sponsor: Robert Black