Radar’s Eye on Wildlife
Biologists harness weather technology to unlock the secret lives of birds, bats and bugs.
By Russell Roe
The next time you watch the weather on TV, you should know that you’re missing something. Something big. The bigger story of life in the air is being ignored — hidden behind the cheerful TV meteorologists, the warm air masses from the Gulf and the picture sent in by one of our viewers. In addition to tracking storms, weather radar picks up aerial wildlife — birds, bats and insects — but meteorologists routinely filter it out or skip over it.
That means you’re missing the drama of life and death, grand voyages and great migrations, the great struggle of life across North America’s aerial landscape.
Too bad for us. Now here’s Tom with tonight’s sports report.
It’s all there on radar: Hill Country bats emerging on their nightly feeding forays, flocks of birds migrating across the Gulf of Mexico and hordes of insects being carried on winds high aloft. Even if meteorologists are ignoring it, biologists aren’t. They’re increasingly using Nexrad weather radar and other radar systems to gain new insight into animal behavior and to observe aerial wildlife in ways that were previously unachievable.
Winifred Frick, a biologist at the University of California-Santa Cruz, came to Texas last summer to count bats — millions of bats. She figured that if meteorologists could estimate the number of raindrops in a raincloud, she could find a way to measure the number of bats in a bat cloud. And if she could estimate the number of bats on a radar image, she could track whether bat colonies were thriving or in decline.
Frick’s work dovetails with previous research done with radar, primarily involving birds. Sidney Gauthreaux, a professor at Clemson University in South Carolina, pioneered the field with his work on bird migration along the upper Texas coast. The use of radar to track bird migration and monitor bat movements has deepened our knowledge of wildlife and led to conservation actions such as purchasing bird migration stopover habitat, guiding wind farm locations and calculating bat benefits in agricultural pest control.
To accomplish her bat-counting task, Frick enlisted the help of Phillip Chilson, a University of Oklahoma meteorology professor who provided a storm-chasing radar truck, and Thomas Kunz, a Boston University bat biologist who brought his bat-counting thermal-imaging equipment.
The biologists and meteorologists converged on Frio Cave, which harbors one of the largest bat colonies in the U.S. and sits along the Frio River between Uvalde and Garner State Park in the Texas Hill Country. Kunz set up his heat-sensing gear outside the cave, near the top of a limestone ridge, to obtain a census of the bats as they left. Chilson parked his truck, normally used for tornado duty, in an agricultural field a few miles away to record radar images of the bats. They would later correlate their data and compare it with images captured by the weather radar station in New Braunfels to obtain a bat count.
For Frick, this method beats standing outside Frio Cave and counting to 1.5 million as fast as she can.
Before sunset, more than a million Brazilian free-tailed bats, also called Mexican free-tailed bats, started to swirl out of Frio Cave in search of that night’s dinner. The bats flew for a short distance in one direction and turned to head south over the ridge. Then they dispersed. We couldn’t see where they went, but the radar could.
“These are small animals, flying high in the sky, and they’re flying at night, so the ability to try to estimate the number of bats flying in the night sky hasn’t really been possible,” Frick says. “The radar really allows us to see a phenomenon that nothing else allows us to really visualize.”
That night at the regional weather radar station in New Braunfels, the bats showed up as a colorful blooming image amid the hills and agricultural lands of the area. The radar picks up the bat emergences from more than a dozen Hill Country caves. “You can see them nightly sort of erupt, these huge blooms of radar reflectivity coming out of the ground,” Frick says.
John Arvin, research fellow at the Gulf Coast Bird Observatory, tracks birds (and sometimes bats) on radar from his home in South Texas. He says watching the Hill Country bat emergences erupt on radar is “just like watching popcorn pop.”
Jon Zeitler of the National Weather Service in New Braunfels says his office regularly gets calls from people who see clear skies outside but at the same time observe a series of storms suddenly popping up on radar in the Hill Country. It’s the bats.
Meteorologists filter out such biological data to focus on weather patterns, but biologists want to reverse that and study the radar castoffs — the biology of the sky.
Radar works by transmitting a signal into the atmosphere and listening for a returned signal. When the pulse hits a target, a small amount of the pulse is reflected back to the radar. The objects causing the reflection can be raindrops, birds, dust or anything in the atmosphere.
With a trained eye, observers can tell the difference between raindrops and birds on a radar image. “Big movements of birds have a particular stippled pattern to them,” Arvin says. “You can easily distinguish between birds and rain showers because rain showers make these big, blocky-looking images that are strongest in the center.”
The system of more than 150 Doppler radar stations provides biological and meteorological coverage over the whole country. And the archive of digital radar data goes back 20 years.
“There’s a true wealth of data here,” Chilson says. “In one sense, you could say this could be one of the largest biological repositories in existence.”
Scientists at the U.S. Geological Survey are developing artificial intelligence software that will distinguish between birds and precipitation on radar, and they hope to dive into the Nexrad archive to develop models for the timing and routes of bird migration. USGS scientists have also formed a collaborative to share their radar research, including a project documenting migration patterns and stopover habitat in the borderlands of the Southwest.
Frick, Kunz and Chilson aren’t just bat counters. They’re also interested in how wind, rain and other factors affect the timing and direction of bat emergences, and weather radar gives them the answers.
Frick has used weather radar to study how drought and rain influenced bat behavior at Frio Cave. She looked at daily radar data and found that bats emerged earlier in dry years than in wet years.
“In dry years, they’re more willing to face the increased risks of predation by emerging earlier because they have physiological needs that need to be met,” Frick says. “In the wet years, they’re more willing to wait till later to come out because they know they’ll get full tummies.”
That predation was on display on the night I visited Frio Cave. It was a dry year, and the bats were coming out when it was still light outside. As the bats emerged from the cave, a red-tailed hawk repeatedly dive-bombed into the bat cloud in an attempt to get dinner.
Kunz and Jason Horn of Boston University have tracked the migratory pulse of bats in Texas by studying archived Nexrad data. They observed radar activity over known bat sites for a period of months and found that as the bats arrived from Mexico, they tended to stop at bridge colonies, such as Austin’s Congress Avenue Bridge, before moving on to the Hill Country caves. When they migrated back to Mexico, the pattern was reversed.
Spurred by radar images of bats and migrating moths thousands of feet in the air, Texas researchers, including the Texas Parks and Wildlife Department, showed that Hill Country bats save farmers millions of dollars by gobbling up crop-eating insects, underscoring the need to protect large bat colonies.
The radar research being done on bats, birds and insects is part of an emerging discipline called aeroecology, which aims to unify the study of aerial wildlife the way marine biology did for the sea. Most people think of bat habitat as a cave and bird habitat as a forest or wetland. But birds and bats spend much of their time in the air, and aeroecology blends meteorology and biology to study the near atmosphere as habitat and to look at animal interactions there.
New developments in radar could very well mean major advances in the field. The next generation of weather radar, coming this year, is called dual-polarization, which will transmit waves vertically in addition to horizontally. It’ll be like seeing in two dimensions instead of just one. Distinguishing between birds, bats and rain will suddenly get much easier.
Already, radar has helped unlock some of the mysteries of bird migration. Texas sits in a crucial spot for millions of migrating birds, and it’s where the study of radar and wildlife really took off. Much of what we know about the details of bird migration we’ve learned from Gauthreaux and his radar studies along the Texas coast, Arvin says.
“He discovered pretty much everything that’s known about it now — the timing, the altitude of flight, all those kinds of things that we kind of take for granted as common knowledge,” says Arvin.
Gauthreaux’s radar studies led to some major Texas conservation actions. Millions of birds cross the Gulf of Mexico in the spring on their way to their nesting grounds, and they need a place to stop and rest after the exhausting journey over the sea. Where do they stop? The upper Texas coast. Gauthreaux, using radar, was able to map the important stopover sites for the birds, and the U.S. Fish and Wildlife Service targeted those areas for protection. The USFWS has acquired 20,000 acres under a land acquisition program spurred by the birds, and it hopes to acquire 50,000 more. The forested areas along rivers were found to be magnets for migrating birds — places that are vital for the birds to replenish their energy reserves so they can keep on migrating.
“What’s been very important in Texas is protecting some of the important stopover areas in the greater Houston area — the Columbia bottomlands, adding sections to the national wildlife refuge, the Trinity River area,” Gauthreaux says. “All of those are projects where weather radar showed them how critically important those stopover areas are. In terms of conservation achievements, that’s one of the biggest for the state of Texas.”
Watching wildlife on radar isn’t new, but it’s gaining momentum. Gauthreaux thought he could see birds on radar even as a high school kid in New Orleans in the 1950s. The development of digital Doppler radar in the early 1990s revolutionized the field. The Doppler technology meant that researchers could determine the direction and speed of objects in the atmosphere, and Doppler’s digital aspect meant they could download files and store them easily (Gauthreaux no longer had to take photographs of the radar screen). Plus, everything was now in color. The advent of the Internet meant anyone could have access to radar images.
Radar can help bird watchers, too. Several areas of the country have radar watchers who relay their findings to local birders. Arvin, the ornithologist and research fellow, makes a daily radar report on a Texas bird-watching listserv during spring migration to help bird watchers plan their outings. He lets avid birders know what he’s seeing as migrants make their way across the Gulf. He’s especially alert to weather events that may cause the birds to land, called a “fallout.” Such events may not be optimal for the birds, but for Texas bird watchers, it’s the time to break out the binoculars.
Arvin usually stops doing his daily reports in early May, but last year a late storm got his attention: Incoming trans-Gulf migrants were about to reach the coast just as a line of thunderstorms was moving into the area – prime conditions for a fallout.
“There is … an honest to goodness squall line that stretches from Laredo through College Station,” he wrote. “All three Texas radars are showing incoming migrants on a collision course with this line of strong to severe thunderstorms. … That birds will be in a fallout mode this afternoon along the coast is a foregone conclusion.”
Birders took note. It was “very birdy this morning,” one poster commented on the listserv the next morning. A warbler watcher noted: “What a morning!”
Arvin uses a tool we’ve all grown accustomed to from our couches and easy chairs as the TV weatherman waves his hand along a weather map showing the weak cold front moving across the nation’s midsection. It would be great to see Arvin in front of a television camera, with blotches of migrant birds flapping across the gaping Gulf, predicting cloudy skies and a 90 percent chance of warblers at High Island.
As with bats, bird migration presents particular challenges for study. Many migrating birds travel at night, when the atmosphere is more stable but when direct observation is impractical. And they travel at altitudes where direct observation is challenging.
Biologists such as Gauthreaux are using radar to determine basic biological questions about birds and migration — when they migrate, the magnitude of yearly migration, how weather affects migration.
“Birds are incredible at being able to detect the most favorable altitude to migrate, based on the structure of winds aloft,” Gauthreaux says. “Radar was really instrumental in allowing us to discover that.”
And they’re working on direct applications, too — using the knowledge to guide wind farm locations and prevent bird-aircraft collisions. By knowing migration corridors and influences on migration, wind farms can be placed where they will have the least impact on migrating birds, and airports can go on alert when migration is at its peak.
When wind farm companies started proposing projects along the coast, Kathy Boydston of the Texas Parks and Wildlife Department started worrying about the birds.
“We funded one of the first attempts of using radar to track the bird migration corridors along the Texas coast,” Boydston says. “Basically what we were trying to do is track to see what influence weather and vegetation and topography had on migration corridors.” She wanted to use that knowledge to help guide the decisions made by wind companies.
The winds that help the birds during migration are the same winds that companies want to harness to produce power. That’s the conflict. The coastal Peñascal energy farm was built in a migration corridor but made a concession: In what’s believed to be a first for the nation, it’s putting radar to use to avoid bird fatalities. The wind farm uses a radar system to detect incoming birds and analyze weather conditions, and if the birds are in danger of flying into the turbines, the turbines will be shut down.
TPWD gave a grant to Bart Ballard of the Caesar Kleberg Wildlife Research Institute at Texas A&M-Kingsville to track birds along the coast. He set up mobile radar units — smaller than Nexrad and better for tracking individual animals — at the King Ranch and the Laguna Atascosa National Wildlife Refuge in 2007, 2008 and part of 2009. What did he find?
“We learned that we’ve got one of the highest migration passage rates in the world here along the Texas coast,” Ballard says. Warblers, ducks, hummingbirds, swallows and raptors — they’re all flying through.
Ballard has been analyzing the results to learn more about birds and weather and is hoping to fire up the radar system again for more migration studies.
With biology’s expanding role in radar, is it time to rethink the main purpose of radar? Chilson, the Oklahoma meteorologist, offers this thought about what the future might hold as radar biology spreads: “With time, people might start calling these ‘environmental radars’ instead of ‘weather radars’.”
Either way, the next time you watch the weather on TV — after the city council news and before the nightly basketball scores — be sure to think about the birds and the bats.