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Meteorologists use Doppler radar to paint a picture of winds inside a thunderstorm. But they have to be careful to screen out birds — which can look like giant raindrops. A scientist talks about radar and birds …
Using radar to help track birds has been around for almost 60 years. It started in England, where some researchers saw what they called “angels” on military radar. Radar was first used to identify potential collisions with low-flying aircraft, but it’s now being used to conserve migratory birds.
Sarah Mabey is the David Smith Conservation Science Fellow of North Carolina State University. She helps monitor 11 radar stations in the southeastern U.S., using the data to map areas where migratory songbirds concentrate during fall and spring migrations. With radar, this can be done even though the migrating birds are flying under the cover of night. These birds spend their daytime hours feeding, and sleeping, and getting ready for another night of migration…
Mabey: In the evening, just after dusk, the birds take off — they leave these habitats and enter up into the atmosphere. And the radar will pick them up as they enter the radar beam. And they display as these bright areas on the radar screen. So you can identify areas where the birds have really concentrated…
More about where these birds are going — on the next article.
Radar Ornithology has been around for the better part of the last 60 years. It really started in England, with some researchers seeing what they called “angels” on military radar. And they followed up and found out that these were actually birds. That was the very beginning of radar ornithology. In the United States, it’s had a waxing and waning time. But about 10 years ago, NOAA brought online a national network of Doppler radars, what are called weather surveillance radars. And they called them the Next Generation radar, NEXRAD, because they had this Doppler capability. And, of course, NOAA was very interested in tracking severe weather. But there were a couple of researchers in this country who saw the potential for using this radar network to look at bird migration. And the radar, just a very simple technology, in the most basic sense, the radar emits energy, a microwave, that goes out into the atmosphere and hits a particle, and then some of that energy is then reflected back and picked up by the antennae of the radar. Birds are just like a big raindrop out there in the atmosphere. And, of course the weather people who also use the NEXRAD Doppler radars to tell you what your weather is going to be like for the rest of the week, they don’t like birds in their imagery. So, weather people work really hard to eliminate birds from their data. And we as weather ornithologists are interested in eliminating weather from the radar imagery and just picking up the biological targets, particularly the birds. But Doppler radar can pick up insects in the atmosphere as well as birds, so it’s highly sensitive. The work that I’m doing uses this NEXRAD network in the Southern Mid-Atlantic. I’m monitoring 11 radar stations and collecting data from those stations, and using the data to map those areas where migratory songbirds concentrate during fall and spring migrations. And you can do this because the migratory birds are flying at night. They land sometime in the very early morning. And they chose those habitats that are best suited to their needs. They spend the daytime hours feeding, and sleeping, and getting ready for another night of migration. In the evening, just after dusk, the birds take off — they leave these habitats and enter up into the atmosphere. And the radar will pick them up as they enter the radar beam. And they display as these bright areas on the radar screen. So you can identify where the birds have really concentrated — where there’s a high abundance of birds — because they light up on the radar screen, at brighter colors, which relate to the target densities that the radar is picking up. And by taking this information, and then referencing it to the geography, you can build a map of where the birds have concentrated during the day. And the work that I’m doing, I’m seeking to integrate these migratory birds’ stopover concentration areas with land cover information and land use information. And the goal of my project is to help conservation practitioners design a regional conservation plan for migratory land bird stopover points.
Pairing visual observation with radar better check on data, which species – not right tool for looking at birds on the ground.
There are two things here. One is that we have a pretty poor understanding of how migrations work. A lot of people talk about migratory pathways, or migratory routes. And this comes from what we understand about waterfowl, mostly. And we don’t think that this same concept applies as well to migratory land birds, particularly to songbirds, who we think migrate with more of what we call a “broad front” migration, which means that they’re dispersed across the landscape. And so if we want to understand how birds move, in relation to the landscape, in relation to geography and weather, than we do want to track them while they are actually flying. And Doppler weather surveillance radar can help us do that, because it has the wonderful feature of giving us directionality of moving targets, and for instance, Dr. Sydney Gauthreaux, who’s from Clemson University, is using the NEXRAD system to look at bird movements during the peak hours of nocturnal migration, looking at those areas where the greatest number of birds are moving, and looking at the orientation of those birds relative to major features of the landscape, like coastlines, mountains. And that helps us to understand bird migrations generally. The work that I’m doing with radar is more focused at looking, not at what the birds are doing when they are actually in flight, but the way, a sort of proxy for where they have been during the day. And you could rely on bird-watchers to tell you where are the most important stopover concentration sites. But, a nice example shows why you can’t always rely on on-the-ground observers. Just to take an example from the Gulf Coast. Now, a lot of bird-watchers, or birders, will tell you that High Island on the coast of Texas, is one of the most spectacular places to see a diversity of songbirds in the spring. The birds are migrating over the Gulf of Mexico. They hit bad weather, and they drop down on that coast in huge numbers, and this is what we call a “fallout.” Well, Dr. Gauthreaux’s work with Doppler radar has shown that the majority of Trans-Gulf migrants are actually over-flying the coast, and they’re landing some 50 miles inland, in places like the Columbia bottomlands, or the Atchafalaya Basin. These expensive areas of old-growth bottomland forest. And so while the bird-watchers are there on the coast, the majority of the birds are actually in these fairly inaccessible places. ^^^ And I’m finding similar patterns in my own work in the southern mid-Atlantic region, where birds do concentrate along the coast, but if you compare those coastal concentrations with an area like, say the