The tiny tracking units known as light-level geolocators have delivered yet another surprising insight into the migration and winter ecology of Veeries.

The first breakthrough came in 2009-10, when wildlife ecologist Christopher M. Heckscher (PDF) and colleagues from Delaware State University and the British Antarctic Survey revealed not only the path that eastern Veeries took while migrating south to Brazil, but also that they made an additional migration to a second winter site before returning in the spring.

The study was the first to show that a North American-breeding Neotropical songbird occupied two widely separated wintering sites. We reported Heckscher’s findings in “Birding Briefs” in our December 2011 issue.

Now, Keith A. Hobson and Kevin J. Kardynal, researchers with Environment Canada in Saskatoon, have used geolocators to reveal the routes, stopovers, and winter distribution of Veeries that breed west of the Rocky Mountains.

In June 2013, they captured 22 Veeries breeding in the Okanagan Valley of British Columbia and fitted them with geolocators. Then, the following spring, they captured nine of the thrushes and retrieved the data stored in their backpacks.

The researchers write in The Auk: Ornithological Advances that they expected the birds to avoid crossing the Gulf of Mexico when migrating in fall to South America — that is, that they would fly south along the west coast of the United States and over land through Central America.

Instead, the Veeries followed an ancestral great-circle route to the east, traversing the Rocky Mountains and Great Plains before stopping along the Gulf coast from Louisiana to western Florida and then crossing the Gulf of Mexico and Caribbean Sea on their way to south-central Brazil.

Their route was up to 1,600 km (994 miles) farther than that followed by the eastern Veeries, write Hobson and Kardynal, but the western birds arrived within three days of thrushes from the east. And just like their eastern cousins, the western Veeries also moved to a second wintering site, shifting as far as 2,047 km (1,272 miles).

A version of this article appeared in the December 2015 issue of BirdWatching.

How to find Veery and Gray-cheeked, Bicknell’s, Swainson’s, and Hermit Thrush.

 

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Originally Published November 10, 2015