Bay Area Thrushes Nest Together, Winter Together, and Face Change Together

June 18, 2013 — Swainson' s Thrushes, from a local population near Bolinas, CA, spend their winters together in Mexico, according to a new tracking study released by Point Blue Conservation Science, (Point Blue, formerly PRBO). This result is important because it shows how the conservation of habitat for these local populations in California is tightly linked with climate and habitat changes in Mexico, where these birds spend their winters, 1,600 miles away.

The Swainson's Thrush is one of the most melodic of all the songbirds, and can be heard singing now by hikers, walkers, and cyclists enjoying trails near streams throughout the bay area.

Using tiny tags to track a bird's location, biologists from Point Blue have pinpointed the wintering locations of Swainson's Thrushes, tracking them from study areas in Marin County to their wintering homes in central Mexico. Published this week in the journal The Auk, the study illustrates the linkages between nesting and breeding locations of migratory birds. Swainson's Thrushes have lost 95% of available nesting habitat along streams and rivers throughout California. They have also almost completely disappeared from the Sierra, and projections on Point Blue's "Where Will the Birds be" interactive website (choose bird distribution, then riparian, then Swainson's Thrush) illustrates that the Swainson 's Thrush will occur in fewer places in California, given climate change.

Continued

Backpack-toting birds help researchers reveal migratory divide, conservation hotspots

"Birds of a feather do not necessarily flock together," says Kira Delmore, a PhD student with UBC's Department of Zoology and lead author of the paper. 

Pictue: Wikipedia

"Our teams of thrushes took dramatically different routes to get to their wintering grounds, either south along the west coast to Central America, or southeast to Alabama and across the Gulf of Mexico to Columbia." 

The study, to be published this week in the Proceedings of the Royal Society of London B, is the first to collect a complete year's worth of data from individual birds to document such a migratory divide. 

"This detailed level of migration and stopover data helps us pinpoint vital feeding and rest habitats that the birds rely on at key points during their long journey – just before crossing the Gulf of Mexico, for example," Delmore adds. 

The researchers say the study also raises the possibility that migratory behavior may play a role in speciation, the process by which one species evolves into two. 

"Given that migratory behavior is under genetic influence in many species of birds, these results raise the question of what hybrids between these two subspecies would do," says Darren Irwin, associate professor of Zoology at UBC and co-author of the paper. 

"One possibility is that hybrids would take an intermediate route, leading to more difficulties during migration. If so, the migratory differences might be preventing the two forms from blending into one."

Read more at: http://phys.org/news/2012-09-backpack-toting-birds-reveal-migratory-hotspots.html#jCp

More information on Swainson's thrush (Catharus ustulatus):

http://www.allaboutbirds.org/guide/swainsons_thrush/id

http://www.birdweb.org/birdweb/bird/swainsons_thrush