Tiny Bird 'Backpacks' Track Wood Thrush Migrations

Migratory songbirds are disappearing and now, conservationists are taking a closer look at what might be happening to them. The scientists have strapped bird "backpacks" onto wood thrushes to get a better look at their migration.

The researchers traced the 4,000-km route taken by wood thrushes from North America down to Central and South America using tiny geolocators made up of a battery, clock, light sensor, and chip to record data.

"The most challenging thing about these tiny geolocators is that they do not transmit data," said Emily McKinnon, one of the researchers, in a news release. "This means that we put the backpack on the bird, it migrates thousands of kilometers south for the winter, migrates back in the spring, and then we have to catch it again to get the data. The culmination of years of this type of tracking and hours and hours of effort by graduate students, field techs, volunteers, collaborators, and of course our project leader, Dr. Bridget Stutchbury, is detailed migration data from more than 100 wood thrushes tracked from 7 breeding sites and 4 winter sites."

So what did they find? It turns out that wood thrushes from Canada don't migrate to the same areas as their counterparts in Kentucky, Virginia and the Carolinas. In addition, Canadian wood thrushes have a longer migratory route.

"Overall we call this pattern 'leap-frog' because the birds breeding the farthest north actually migrate the farthest south, 'leap-frogging' over the southern breeding populations," said McKinnon. "The connections also tended to be predicted by longitude, so that birds breeding further east (and north) spent the winter further east (and south). So if you are Canadian visiting the Mexican Maya Riviera on vacation and you see a few wood thrushes-odds are they are not 'Canadian' wood thrushes, but probably birds from the southern U.S."

The new migratory map could help conservationists better target area for habitat protection.

The findings are published in the journal Conservation Biology.