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Scientists Use Weather Radar to Track Bats

WASHINGTON, D.C.—When Winifred Frick sits down at her computer to look at radar maps, it's not to track a local thunderstorm. It's to follow bats. A bat ecologist at the University of California, Santa Cruz, Frick uses weather radars to monitor the movements of animals that used to vanish quickly from scientists's view as they took to the night sky for daily or seasonal journeys. Her research is part of a new field of study, called aeroecology, that looks at the interactions between flying animals and their airspace. Given the numbers of birds and bats killed at wind turbines, there is a great urgency to better understand the movements of airborne animals.

Frick has discovered that at least one bat species is quite particular about the weather. Brazilian free-tailed bats, common in the south-central United States and Mexico, emerge from their daytime slumber at different times of day depending on the temperature and humidity, as Frick and her colleagues will report here Saturday at the annual meeting of the American Association for the Advancement of Science (which publishes ScienceNOW).

Radars are a window into airspace. They send out radio waves that reflect off raindrops, airplanes, bats, and so forth. To predict storms, meteorologists must filter out reflections from organisms. So what Frick needs are the unfiltered raw data, which are less readily available. Until recently, researchers could typically look at information from just a few places for a few points in time.

At the meeting, Frick and her colleagues described a new Web portal, called Surveillance Of Aeroecology using weather Radar, that makes using radar data much easier for biologists. To compile weather and flood information used by forecasters around the country, the National Severe Storm Laboratory in Norman, Oklahoma, stitches together data from 156 NEXRAD radars from across the United States and overlays the filtered information on a U.S. map. Researchers can look at the big picture or zoom in to a particular locale. The data are updated every 5 minutes, and all of the information is archived.

Now the lab is making it easy for researchers to download and use not just data processed for meteorologists, but the unfiltered data as well. And in the next few years, those radars will be upgraded. The new equipment may allow biologists to tell birds, insects, and bats apart, something they can't do right now.

"It's a tool that can be used by lots of people to ask a variety of different questions," says Frick. "It will really open up the field."

With a few strikes on her keyboard, Frick was able to call up daily radar data that covered a bat cave in Texas. That data showed what time the bats emerged from the cave for their nightly insect hunts. It was very dry during 2009 and 2010 was very wet, allowing her to get a sense of how the climate affected emergence time. During the dry year, the bats tended to come out relatively early, and hotter days meant even earlier starts, she found. But during wet years, hot days resulted in late starts. "How local weather affects the bats depends on the seasonal climate," she explains.

The bats are balancing the need to wait until dark, when day-flying hawks stop hunting, and the need to catch the insects when they are most plentiful, right at dusk. Also, dehydration is a factor on hot days. In moist years, the bugs thrive, so there's more to eat and insects stay active longer on hotter days. But in dry years, water stress and fewer insects make the bats come out earlier, says Frick.

"We've been limited in the past in that we haven't had very good methods for seeing up in the night skies and the air above us," says Paul Cryan, a research biologist at the U.S. Geological Survey in Fort Collins, Colorado, who is not connected with the work. Now with the easier access to radar data, Cryan says that researchers such as Frick "are just starting to see patterns that are meaningful."

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