Boston Blog

How now, brown-headed cowbird?

With help from hundreds of volunteers, Mass Audubon is tracking the health of dozens of the Commonwealth’s breeding bird species.

Jennifer Weeks

Wild turkeys are up, kestrels are down, and robins are holding steady. These are some of the early findings from Breeding Bird Atlas 2 (BBA2), a five-year initiative by Mass Audubon that began in 2007 to measure bird population trends across Massachusetts.

BBA1, conducted from 1974 through 1979, was the first effort in North America to map the status of breeding birds systematically across an entire state. BBA2 is already showing how large-scale landscape changes over the past 30 years have affected wildlife. The results could help the state government and Mass Audubon formulate better environmental and conservation policies.

The atlas approach, in which volunteers survey 10-square-mile blocks across the state during breeding season for five consecutive years, is a way to measure the health of breeding bird populations on a large scale. “When you assess the condition of any population, you need to know how quickly members reproduce and die and the area over which they do it,” explains project coordinator Joan Walsh.

According to data collected in 2007, more than half of the Commonwealth’s breeding bird species are either stable or increasing. But others are declining at sharp rates, including meadowlarks and kestrels, both of which rely on shrub lands and open grasslands–habitats that have shrunk across Massachusetts due to residential and commercial development. National studies by the US Geological Survey have also recorded declines in these species.

The numbers of American kestrels (top), eastern meadowlarks (middle), and short-eared owls (bottom) appear to be declining in Massachusetts, according to the Mass Audubon’s Breeding Bird Atlas 2. (Credits: US Fish and Wildlife Service and Mass Audubon/David Larson)

Other species, including some that once were essentially extinct across the Northeast, are thriving now, including wild turkeys, red-bellied woodpeckers, and Cooper’s hawks. All three of these species are benefiting from the fact that forests, where they nest and hunt, have been growing back on abandoned Massachusetts farmlands over the past century. “The winners are birds that profit from human alteration of the landscape,” says Walsh. “Carnivores and fish-eaters are also doing much better since our pesticide and water-quality laws improved in the 1970s and 1980s, because they aren’t bioaccumulating as many toxics as they used to.”

Spot the bird

Birders use protocols adapted from British surveys, such as standardized classification strategies and codes. For example, “P” indicates a pair seen together in a suitable nesting habitat, while “S” stands for permanent territory, presumed through hearing a specific bird’s song at the same location seven or more days apart.

The atlas is designed mainly to inform conservation policy decisions. Mass Audubon is the second-largest private landowner in the state, so BBA2 may influence how it manages its own sanctuaries. The group will also use the bird data to advise state agencies that manage public lands and wildlife, says Walsh.

BBA2 will also help evolutionary biologists confirm long-term trends. “An atlas adds a geographic component to bird population databases,” says Trevor Lloyd-Evans, director of the bird-banding program at the Manomet Center for Conservation Sciences near Plymouth, MA. “Doing it a second time makes it really useful because that documents changes in populations and ranges, which either oppose or confirm what we’re seeing in our own work.”

BBA1 data is available on the state-run MassGIS website, assembled by the Executive Office of Energy and Environmental Affairs to support environmental planning and management, and will be updated with BBA2 counts. Correlating bird population trends with land-use changes helps regulators come up with policies to address major sprawl zones such as southeastern Massachusetts, which used to be mainly agricultural but is now one of the fastest-growing regions in the state.

Pooling data

Since the 1980s, most US states and Canadian provinces have completed their own breeding-bird atlases. When BBA2 is complete, Mass Audubon plans to integrate its numbers with those from Ontario, Vermont, New York, Ohio, Pennsylvania, Maryland, and Washington, DC, to create a contiguous data set for the Northeast. It will require a lot of coordination and management, but if done right, says Walsh, “I think it will be one of the best databases on bird changes in the world.”

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