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Tiny GPS tags are huge for the study of small birds

Ovenbird in Big Pine Key, Florida, by marian mcsherry.
Ovenbird in Big Pine Key, Florida, by marian mcsherry.

Our ability to describe exactly where a bird spends the winter, the routes it flies while migrating, and the timing of its movements has just taken a quantum leap forward. For the first time, a small migratory bird has been tracked using the super-accurate Global Positioning System.

Since satellite-based GPS technology became fully operational in 1995, it has been integrated into almost every facet of the world economy and revolutionized countless aspects of our daily lives, from cell phones to turn-by-turn driving directions. Yet its usefulness to wildlife studies has been limited.

The technology can provide locations with an accuracy of about 10 meters (33 ft), but until recently, the smallest model weighed about 12 grams (0.42 oz). Consequently, it could not be used safely on animals that weighed less than 250 grams (almost 9 oz), a little less than the weight of a Pileated Woodpecker.

But now a miniaturized unit an order of magnitude smaller than previous devices has become available. Weighing only about a gram, it can be worn safely by animals that weigh as little as 20 grams (0.7 oz), or about the size of a large warbler.

Wildlife biologists from the Smithsonian Migratory Bird Center used the tag recently to pinpoint the nonbreeding locations of Ovenbirds captured in Maryland and New Hampshire that weighed more than 20 grams. The Maryland breeders flew to Florida and western Cuba. The northern birds migrated farther, taking up territories in eastern Cuba, the Dominican Republic, and Haiti.

Obtaining information so detailed from light-level geolocators or stable isotopes would have been impossible, write researchers Michael T. Hallworth and Peter P. Marra in Scientific Reports. “Non-breeding location data for Ovenbirds analogous to those obtained with GPS tags (~10m) would involve weeks of costly, labor-intensive fieldwork,” they conclude, “and the breeding origin of these individuals would be unknown.”

“The high-resolution tracking of a small migratory songbird, from a breeding to a non-breeding territory at 10 m accuracy, is a major step forward for understanding the ecology of small migratory animals,” conclude Hallworth and Marra. “Continued improvements in this technology will further increase our ability to answer complex questions with regard to seasonal interactions and population dynamics and hopefully help in our ability to conserve migratory species.”

Read the report

Michael T. Hallworth and Peter P. Marra. 2015. Miniaturized GPS Tags Identify Non-breeding Territories of a Small Breeding Migratory Songbird. Scientific Reports 5, article number 11069; doi: 10.1038/srep11069.

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

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