Ask an expert birder about the best time to experience prime migration, and they might answer with a detailed explanation about weather conditions that could leave a new birder’s head spinning. Tracking the weather to choose the optimal birding window can practically require a degree in meteorology: What’s the temperature? Know the wind speed and direction? Any rain on the horizon?
Thankfully, since 2018, rookie and experienced birders alike have taken advantage of a simpler method: BirdCast. Created by the Cornell Lab of Ornithology, BirdCast forecasts the intensity of overnight bird migration across the continental United States, displaying waves of migratory birds on a series of easy-to-read forecast maps. Now, with the release of a slick new migration dashboard this spring, the BirdCast team has made it even easier for anyone to predict if they’ll have a birdy morning.
The standout feature of the migration dashboard is that it provides users the ability to localize the data, letting you zoom in to your state or county to see estimates of how many birds are migrating at night—and in real time. The tool also displays the birds’ flight direction, speed, and altitude, providing birders with more information for deciding when and where to bird during the migration seasons. “With the dashboard you can understand something about what those numbers are doing and what's happening as it's happening,” says Andrew Farnsworth, an ornithologist at the Cornell Lab of Ornithology who spearheaded the new tool’s development.
While spring and fall migration progress in roughly similar patterns each year, no two spring or fall migrations may be identical because of changes in bird abundance, weather conditions, and even shifts in the timing as the planet warms. “Just appreciating how dynamic migration is on a day-to-day level—it’s something that this kind of insight can provide, which I think is really cool,” says Benjamin Van Doren, who worked on BirdCast as a Cornell University undergraduate and now as a postdoctoral researcher at the Cornell Lab of Ornithology.
The simplicity of the bird forecasts betray the complex mathematical processes that underlie them. BirdCast was just a glimmer in scientists’ eyes in the late 1990s, when migration predictions were essentially being hand drawn using limited data inputs. The ability to estimate the numbers of migratory birds became a real possibility in 2010 with advances in technology, cloud computing, and machine learning that allowed scientists to fully harness a powerful data source: weather radars.
A network of 143 radars, managed by the U.S. government, dots the continental United States, collecting information about the atmosphere, such as rain and wind, and also some biological data, including the movements of insects and birds. Scientists had already been researching how these radars could help them better understand bird migration, but separating the two data types was a major hurdle. Van Doren and Kyle Horton, a former Cornell postdoctoral researcher and now an ornithologist at Colorado State University, overcame the challenge by using advanced machine-learning techniques to analyze two decades of bird and weather data. Their efforts revealed that the number of migrating birds each night could be explained mainly by atmospheric conditions. “That was a huge leap forward,” Farnsworth says.
The pair then created forecast models, combining the bird data from weather radars with meteorological weather forecasts. Iterations of these maps have guided birders since Van Doren and Horton's research went public with the launch of the BirdCast website in 2018. Since then, Farnsworth has brainstormed other ways to show the scale and magnitude of migration, but it wasn’t until late 2021 that the dashboard was conceived under the data visualization expertise of Audrey Carlsen. In only six months, Carlsen and her team working closely with Farnsworth and others managed to complete the tool just in time for spring migration. “It's a unique opportunity to educate and make people aware,” Farnsworth says.
The technology’s central innovation is its numerical estimates of how many birds flew overhead the previous night—or, if you visit the dashboard after sunset, how many are passing over at that very moment. The dashboard might show just a few thousand birds migrating over New York County, for example, but more than 8 million birds for the entire state of New York. And on one of the busiest nights this May, BirdCast predicted more than 400 million birds were on the move across the continental United States. “It's important [to remember] that it is an estimate, we're not actually standing out there, counting bird by bird,” Carlsen says.
The original forecast maps only show migration intensity ranging from low to high, so seeing a number is a major addition. “There is just something that is more dramatic about seeing an actual number,” says Bradley Wilkinson, a birder and ecologist at Duke University. “It brings home the immensity of the event that’s happening.”
BirdCast’s forecasts and new dashboard are helping novice and experienced birders appreciate migration this spring. “It’s amazing,” says Anna Vallery, a passionate birder and conservation specialist at Houston Audubon. “Even if you are stuck at your computer working, you feel like you can be a big part of migration happening by tracking it through this crazy technology.”
For Wilkinson, BirdCast has been a game changer for his birdwatching—and getting his family to join in on the spectacle of migration. “It’s hard to overstate my enthusiasm for BirdCast,” he says. He tries to go outside and bird more during stretches when BirdCast has predicted big pushes of migrants. “I think having that specific number attached to it has made [them] understand the magnitude and scale of the event in a much more profound and real way,” Wilkinson says.
How to Get the Most Out of Birdcast
Night before birding: BirdCast forecasts migration for three upcoming nights, so start planning early. The night before a possible outing, pull up the static forecast maps that display the migration intensity to get a big-picture view of bird traffic across the continental United States. Warm colors indicate more birds will pass overhead, while cool colors suggest little migration activity. Bright white, the highest level of intensity, “means get up early and go birding in the morning, because there is likely going to be a lot of birds coming through,” Vallery says.
Next test out this year’s new tool: the migration dashboard. Plug in your county to access hyperlocal information. The extra features on the dashboard, like the birds’ altitude and expected migrants, can help you fine-tune your plans. Intuitive charts show the current season’s data as well as historical migration movements. The dashboard includes estimates of how many birds recently flew through the area and when peak migration occurred, as well as their flight direction, speed, and altitude. “All that can inform where you are going to go birding and how you are going to go birding,” Farnsworth says.
Feeling ambitious? If you see large numbers of migrants on the dashboard’s live feed at night, consider stepping outside to listen for the chip notes of birds flying overhead. You could even try your hand at recording those nocturnal flight calls or watch for migrants passing in front of a full moon. “It is really cool to verify [the numbers] in real time,” Wilkinson says. “I can set up my spotting scope on the moon, and visually confirm all these birds flying over.”
Morning of birding: A high number of birds the night before suggests it’s worth getting up to go birding in the morning. Before heading out, check the altitude chart to see whether the birds likely stopped over, Farnsworth suggests. If migrants drop in altitude overnight, a favorite patch is more likely to be dripping with birds. If altitude remains high, though, you will likely still have some success, but keep in mind that birds may have passed over your county and skipped your local birding spot.
Also, check the list of expected nocturnal migrants on the dashboard. Checklists submitted during eBird’s 20-year history provide an idea of what species will likely be around in each county throughout the migration season. For new birders, some idea of what species to expect can help with ID. If you seek a favorite bird on the list, you could visit that bird’s preferred habitat, or you might want to commit to spending more time birding that day.
All migration: The dashboard can also be a tool for conservation. Collision risk with buildings increases when birds fly at a low altitude, so during migration, you can use high numbers of birds and altitude as clues to turn off unnecessary lights. Live near an urban center? The morning after a big migration event, consider patrolling the perimeter of large buildings to help injured birds (or count and record dead ones) that collided overnight. Cats kill millions of birds each year, so seeing high numbers of birds on the dashboard is a good reminder to keep your cats inside.
A word of caution: While the forecasts are fairly accurate—about 75 percent, according to Van Doren—they aren’t perfect. “Whether or not birds show up at your backyard or at your favorite birding hotspot is a different, challenging question,” Horton says. “But that’s the fun of it, trying to figure out the mystery of migration.”