How a small bird is helping to save its grassland habitat

In an effort to retrieve tiny geolocator devices, researchers returned to NAS Patuxent River recently to recapture a number of grasshopper sparrows that had been banded and tagged with the devices last year. Because the device could not exceed 4 percent of the bird’s body weight, only the heavier males were tagged.

We’ve all heard the expression “a little bird told me,” but it’s precisely the information a little bird can tell us that has an avian ecologist and two assistants treading through the grassy areas surrounding the NAS Patuxent River airfield.

Operating on a grant from the Department of Defense Legacy Resource Management Program, Daniel Kim and his team, working with the Vermont Center for Ecostudies, are looking to recapture many of the 30 grasshopper sparrows that were caught, tagged and banded here last year.

“These birds are grassland breeding birds and grasslands are the most endangered ecosystems in the world,” Kim said. “Grasslands are generally on good soil that gets readily and quickly converted to agriculture; or they’re in areas where there are a lot of people and get converted to cities. Approximately 95 percent of the world’s grasslands are no longer native grasslands.”

Grasshopper sparrows are not a rare bird; they’re very common, Kim noted, but since the 1960s, their population has declined an average of 3 percent a year.

“If you think about how interest works, a 3 percent decline means that about every 21 years, that population is getting cut in half,” he said. “We aren’t creating more grasslands, we’re watching them shrink and this bird is one of the species that will lose out bigtime when their habitat is no longer suitable for them to nest.”

Pax River, with its isolated and relatively undisturbed grasslands, serves as a perfect research area for the bird study.

“Around airfields, the grass tends to stay grass and at a relatively short length, which allows for stability and presence of habitat for the grasshopper sparrow to use year after year,” Kim explained. “And with not a lot of grassland area outside of the base, they don’t have anywhere else to go. Pax is basically a grassland in the middle of a forest. If they’re coming back, you’ll probably find them here.”

In 2015, each captured bird was tagged with a tiny geolocator device that fit like a harness over its thighs and rested on its back — and it’s those geolocators, and the information they’ll provide, that the group is here to retrieve in 2016.

Kim explained the geolocators do not use or transmit any kind of signal. Instead, they record ambient light over long periods of time and by using that information to acquire latitude and longitude, scientists are able to accurately determine what areas the birds have visited.

“If we can see where these birds are breeding and, more importantly, where they’re going — if there are areas of regional or national importance where they stop over during migration — it will allow us to make management recommendations on a regional or even continental scale,” Kim said. “Natural resources management, like everything else, is underfunded. But if you can identify and target high value areas to protect, then you can get the most out of your conservation buck.”

In the two weeks the team has been here, they’ve seen 12 tagged birds and recaptured 11 of them by playing a recording of the male’s song.

“The males are very aggressive and when we play the recording of another male, they’ll get worked up and come right toward the speaker and hit the net,” Kim said. “Five minutes later, after we take measurements and remove the geolocator, they’re free and off again.”

Grasshopper sparrows pose no threat to installation aircraft.

“They’re not much of a strike hazard due to their very small size and non-flocking habits,” explained Pax Conservation Director Kyle Rambo. “Their numbers are actually an indicator of a safe, well-maintained airfield, and results from this study may help us better manage the species for both conservation and airfield safety.”