This animation illustrates the use of a network of surveillance weather radar to record nocturnal migrating birds, bats, and insects in the continental U.S. from sunset to sunrise Oct. 1, 2008. The blocky green, yellow, and red patterns, especially visible on the east coast, represent precipitation; but within an hour after sunset, radar picks up biological activity, as seen in the widening blue and green circles spreading from the east across the country. The birds, bats, and insects take off, fly past, and get sampled by the radar beam. Note, the black areas on the map do not represent places without birds, necessarily, but rather places where radar does not sample.

CORNELL (US)—Are wind turbines hazardous for migrating birds, two-thirds of which travel at night? To answer that question, researchers are using radar and newly developed listening devices to map migration patterns.

Radar, combined with state-of-the-art bioacoustic listening devices, could be an effective way to record birds’ flight calls at night and then quantify and identify species migrating past potential and existing wind-power sites, says Chris Clark, director of the Bioacoustics Research Program at Cornell’s University’s Lab of Ornithology.

Clark and Andrew Farnsworth, a postdoctoral associate at the lab and an expert on migrating birds, have developed listening devices as well as the software to analyze them.

Data from the network of weather surveillance radars in the continental U. S. can be superimposed over a map of the country to track night-time migration. On Oct. 1, 2008, researchers recorded movement of 2,000 birds per cubic kilometer in some of the most densely traveled areas.

“You’re talking about a massive movement of birds overnight,” Farnsworth says. The risks that wind turbines pose for migrating birds is not clear, Farnsworth adds, but migration pathways tend to overlap with high-wind areas that have the greatest potential for wind-energy development.

Radar data—which can show the magnitude, location, timing, speed, and direction of migration patterns, and provide information on key stopover sites—along with data from flight call recordings and tracking tags on birds will allow researchers to identify many species in key areas.

Clark adds that recorders are cost effective, can be automated for many months at remote sites, provide data on many species simultaneously, increase the probability of tracking secretive and endangered species, and will allow regulatory agencies to develop computer models to assess risks to birds from wind turbines.

But using such acoustic technology could produce a massive “data crunch.” A single microphone over a three-to-four-month period can record 120 to 140 gigabytes of data. Collections from several hundred microphones would require advanced software to process the data volume.

Researchers will need to better recognize the wide variety of flight calls and learn to integrate data from radar with those from acoustics and tracking tags, Clark explains, adding that more research is needed to determine at what altitudes species tend to fly and whether birds sense turbine blades and avoid them.

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