Science for a Blue Planet

Science for a Blue Planet

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New Micro-technology Tracks the Secret Paths of Songbirds

By | February 2, 2015

Hermit Thrush again

Technology is helping us learn where songbirds fly.

Until recently, tracking devices were too heavy for songbirds to carry, so it was a mystery where these birds went after leaving our yards or nearby natural areas.

Now, thanks to devices that weigh a gram or less, Point Blue Conservation Science researchers have recorded California populations of Golden-crowned Sparrows migrating to the Gulf of Alaska, the Yukon and British Columbia, Swainson’s Thrushes to western Mexico and, most recently, Hermit Thrushes to British Columbia, Washington and Alaska.

Point Blue Avian Ecologist Renée Cormier says this information is important for helping us understand the connections birds have to different geographic areas. In the context of a changing climate and changes in land use, this can help identify the challenges specific songbird species face, depending on where they travel.

Point Blue Avian Ecologists Mark Dettling and Renée Cormier carefully remove songbirds from a mist net as part of their research.

Avian Ecologists Mark Dettling and Renée Cormier carefully remove songbirds from a mist net, as part of a long-term songbird research program that now includes tracking migration routes.

“Point Blue scientists have studied songbird populations at our Palomarin Field Station for almost 50 years and, yet, we had little information on where migratory birds go,” says Cormier, who has worked at the station, located at the southern end of central California’s Point Reyes National Seashore, since 2002. “New micro-technology is making that possible.”

This technology now includes two different kinds of geolocator tags, both placed on birds as backpacks and strapped in place with soft silicon cord. Point Blue began using light-level geolocator tags in 2010. These tags contain a light sensor, clock and battery, and collect daily data on the bird’s location within 100 miles of accuracy by linking up latitude with day length and longitude with solar noon.

This winter, Point Blue also began research on wintering Fox Sparrows using new, more accurate GPS tags. These tags are pre-programmed to download only eight specific GPS points during the bird’s migration and breeding season but offer accuracy within 20 meters.

Both tags require scientists to catch the backpack-wearing birds after they return to California in order to remove the tags and download the data. Point Blue has not detected any negative impacts of the tags on the birds.

Renée holds the light-level geolocator (left) and the new GPS tag (right).

Cormier holds the light-level geolocator (left) and the new GPS tag (right).

At this time, the tags can only be used on larger songbirds, weighing an ounce or more, such as sparrows and thrushes. The technology will have to get even smaller to be used on lighter birds like most warblers, wrens and nuthatches.

“The research has already provided new insights into songbird migration patterns,” Cormier says. “For example, we found Swainson’s Thrushes have strong migratory connectivity, which means most of the birds we tagged here went to the same area in western Mexico, making them more vulnerable to changes in habitat or climate compared to other species that disperse more broadly.”

Point Blue staff outfitted 35 Swainson’s Thrushes with light-level geolocator tags during their summer breeding season in 2010 and, over the next two years, recaptured 12 of the birds, downloaded the data and found 11 of them wintered in the western Mexico states of either Jalisco, Nayarit or Colima. This information, combined with other similar study findings, illustrates the importance of maintaining habitat in both California and Mexico to help ensure the species thrives in the future.

Unlike the Swainson’s Thrushes, Point Blue researchers found coastal California Golden-crowned Sparrows dispersed over almost 800 miles across the Gulf of Alaska during their summer breeding season, but all to coastal areas. They followed a predominantly coastal route and migrated twice as fast in the spring compared to the fall (averaging 29 days versus 53 days). The inland-wintering Golden-crowned Sparrows showed a different pattern, which Point Blue researchers are still analyzing.

“Until now, we’ve only known half the story of these birds’ lifecycles,” Cormier says. “Over time and research with multiple songbird species, we’ll be able to put a more complete picture together.”

The new GPS tags that gather eight specific points are now aboard 15 wintering Fox Sparrows. Point Blue staff also placed the other light-level geolocator tags on 21 of the birds for comparison. This means that, maybe by this time next year, we’ll also know where California’s Fox Sparrows fly.

 

Main photo: Hermit Thrush with a light-level geolocator.

View a recent San Francisco Bay Area NBC news story on Point Blue songbird research: “Bird Can Tell Us A Lot About the Greater Environment.”

Learn more here about Point Blue’s long-term songbird research at the Palomarin Field Station.

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