Spatial data develops insights into how individual birds behave Every spring, flocks of birds small enough to fit in your hand fly thousands of miles and across continents to hatch the next generation. The vast majority of these birds head for the chilly air of North America, such as Canada, New England and the Adirondack Mountains. But a small segment finds a mate in the mountains spanning Georgia and North Carolina. It’s here, in an area that flirts with cold winters while embracing hot summers, that select Canada warblers and black-throated blue warblers buck the trend of their more northern-bound relatives. “Even though they’re moving thousands of miles, their territory will be within a few meters of where they were the previous year,” says Heather Gaya, a doctoral student in the University of Georgia Warnell School of Forestry and Natural Resources who has been studying the movements of these and dozens of other species that flock to this corner of the Appalachian Mountains every spring and summer. “It’s really fun to map these territories from year to year to see where they’re changing.” From April 15 to July 15, Gaya and other students at Warnell, along with associate professor Richard Chandler, stay in dorms at the Coweeta Hydrologic Laboratory in Otto, North Carolina. They spend their days catching, banding and monitoring 45 different species of migrating birds that come through the area each spring. But they pay particular attention to the warblers, who represent what’s called a “trailing edge population”—they migrate to the extreme southern edge of their range. Decades ago, the birds would take over an entire mountain. Today, as temperatures warm, they migrate to smaller and smaller areas. “You never see them at the bottom of the mountain anymore,” adds Gaya. This makes them an interesting case study in how climate change is affecting their movements and reproductive habits. This is where Gaya’s research is key. Not only are she and her team mapping the large-scale movements of the warblers, which are listed as threatened in Canada, but Gaya is using spatial data to track movements of individual birds. The goal is to develop a reliable model that can be used to predict how populations will respond to future environmental change and management actions. This individual-based model of range dynamics offers a new level of detail into how the birds behave, and it can be important for a species like the warblers, whose already small habitat in the mountains is threatened by climate change. “Individual-based modeling has the advantage in that a lot of interactions happen individual to individual—but it’s also mathematically difficult to model those frameworks,” she says. “So, the goal is to make an easy-to-use framework that people could use for different species.” The study is connected to a larger project that has been directed by Warnell professor Robert Cooper for decades, tracking a variety of species and their response to climate change. Gaya’s spatial component is a more recent development, as technology opens up more avenues to collect data. Understanding and applying spatial technology wasn’t Gaya’s original path in college. As an undergraduate student she studied biology, and when she assisted on a project studying types of grass, she realized how satisfying field work could be—but studying wildlife seemed more interesting. She received an assistantship from Warnell for her master’s degree and worked with Clint Moore, an adjunct associate professor and current acting leader of the Georgia Cooperative Fish and Wildlife Research Unit, to use spatial technology to track gopher tortoises. Working with Moore, she began to understand how spatial technology could benefit species management. “The more I worked with the data, the more sense it made to focus on the spatial aspect,” she adds. Now pursuing her doctorate, Gaya has found her groove analyzing data she and her team collects in the foothills of the Appalachians. Around 80 species of birds migrate through the area, and the team tracks 45 of them. For every bird they catch, they examine its population and follow it over time. The data shows some birds are affected by climate change more than others. Through her research, Gaya has access to about seven years’ worth of information, and it points to more birds struggling in warm, dry years. “They have lower reproduction rates and they’re often stuck up on top of the mountain where they compete for food,” says Gaya. “So, the offspring also compete for food and we see nest failure.” Years where springs are cool and wet also create challenges. For example, on a cool spring day birds may settle into a nest lower down the mountain. But over time, as the weather warms, more birds move into higher elevations. As a result, she says, there are fewer birds in lower elevations without a mate—further complicating reproductive issues. This spring will be Gaya’s third year working on the mountain. Even though there are some challenges brought by COVID-19—for example, the Coweeta facility sees fewer researchers overall, and Gaya’s group becomes their own “quaran-team” during their months there—it’s still an experience she’s excited to take part in. “There’s something about the Appalachian Mountains that attracts diversity; it’s like the perfect system where you can watch changes in real time among so many species,” she says. “And the birds—these are tropical birds, so they’re brightly colored, around 8 to 9 grams, and these gorgeous animals. I think it’s great field work.”
