Raptor migration in the Neotropics: patterns, processes and consequences. Bildstein, K., L. Ornitologia Neotropical, 15(Suppl.):83-99, 2004.
Raptor migration in the Neotropics: patterns, processes and consequences [pdf]Website  abstract   bibtex   
The Neotropics host breeding or non-breeding populations of 104 of the 109 species of New World raptors (i.e., members of the suborder Falconides and the subfamily Cathartinae), including 4 complete migrants, 36 partial migrants, 28 irregular or local migrants, and 36 presumed non-migrants. Standardized counts of visible migration initiated in the 1990s, together with a focused literature search provide an emerging picture of raptor migration in the region. Here I describe the movements of the principal species of migrants, and detail migration geography in the Neotropics. The Mesoamerican Land Cor84 BILDSTEIN ridor is by far the most concentrated migration flyway in the region. Three species of Nearctic breeders, the Mississippi Kite (Ictinia mississippiensis), the Broad-winged Hawk (Buteo platypterus), and the Swainson’s Hawk (B. swainsoni), all of which are complete migrants, together with western North American populations of Turkey Vultures (Cathartes aura), numerically dominate this northern or “boreal” flight. Much smaller numbers of Ospreys (Pandion haliaetus), Swallow-tailed Kites (Elanoides forficatus), Merlins (Falco columbarius), and Peregrine Falcons (F. peregrinus), routinely enter and leave the Neotropics via trans-Caribbean and trans-Gulf of Mexico routes. Southern or “austral” and intratropical movements, including dispersal and colonization in response to habitat change, are known but remain relatively little studied. Having detailed the patterns and processes of raptor migration in the region, I discuss what is known about the ecological consequences of these movements, including competitive interactions between migrant and resident species. I then go on to explore the role that long-distance migration has played in shaping raptor species distributions and abundances in the Neotropics. I conclude by proposing that the hourglass configuration of continental landmasses and the north-south orientation of mountain ranges in the New World, not only facilitate long-distance land-based raptor migration in the region, but also enhance regional raptor diversity via a speciation process called “migration dosing.” The process of migration dosing involves a series of events in which “doses” of diverted long-distance migrants (1) arrive in areas tangential to or beyond their major migration flyways, (2) remain there the following breeding season rather than returning to traditional breeding areas, and (3) eventually diverge from parental stock in geographic isolation. Likely examples of migration dosing are presented from two species-rich near-cosmopolitan genera, Accipiter and Buteo.

Downloads: 0