Migratory strategies across an ecological barrier: Is the answer blowing in the wind?

Abstract

Background: Ecological barriers can shape the movement strategies of migratory animals that navigate around or across them, creating migratory divides. Wind plays a large role in facilitating aerial migrations, and can temporally or spatially change the challenge posed by an ecological barrier, with beneficial winds potentially converting a barrier to a corridor. Here, we explore the role wind plays in shaping initial southbound migration strategy between two populations departing from different locations along an ecological barrier. Methods: Using GPS satellite transmitters, we tracked the southbound migration of two populations of Short-billed Dowitchers ( Limnodromus griseus caurinus ) from breeding grounds in Alaska to wintering sites in coastal Mexico. The breeding grounds were positioned in distinct regions along an ecological barrier, the Gulf of Alaska. Between the two populations, we compared migratory timing, wind availability at, and tailwind support en route across the Gulf of Alaska. Results: Route choice and arrival timing to wintering sites differed markedly between the two populations: individuals departing from the more westerly site (King Salmon) left at the same time as those from further east (Beluga) but crossed the Gulf of Alaska farther west and arrived along the Pacific coast of Mexico an average of 19 days earlier than their counterparts. Dowitchers from both sites used a slight tailwind to cue departure, but once aloft over the Gulf of Alaska, birds from the more westerly site had up to ten times more tailwind assistance than birds from the more easterly one. Conclusions: The distinct migration strategies, and degree of wind assistance experienced, of these two populations demonstrates how differences in wind availability along migratory routes may form the basis for intraspecific variation in migration strategies with potential carryover effects. Future changes in wind regimes may therefore interact with changes in habitat availability to influence migration patterns and migratory bird conservation.