With These Maps, You Can Track Migratory Birds in Near Real Time

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Black-throated green warblers are among the millions of birds that migrate along the eastern coast of the U.S. The new BirdCast tools give bird-watchers a heads-up about when to look for them. Kyle Horton

If you’re a bird-watcher, there's an interactive way to enjoy your hobby thanks to the Cornell Lab of Ornithology.

Cornell scientists created a tool on their BirdCast website (with research funded by NSF, Leon Levy Foundation, Rose Postdoctoral Fellowship and Marshall Aid Commission) that shows in near real-time the volume and direction of migratory birds traveling throughout the country. The migration forecast maps will keep you apprised of what to expect in the days (and nights) ahead.

BirdCast has been around since 2012, but before this year has relied on human input to forecast and assess bird migration. "We’ve always wanted to remove the human element from these predictions, with the hope that we could implement an automated system driven by new and historical data," said Kyle Horton, a post-doctoral research fellow at the Lab of Ornithology in Ithaca, New York.

The tools rely on the U.S.-based radar network, NEXRAD, to measure the flight activity of migratory birds. Using specialized algorithms, the scientists translate the radar information into intuitive maps that indicate the number of birds in the airspace. The large, colored forecast map and the three smaller forecast maps show the predicted intensity of nocturnal migration three hours after local sunset. The maps are updated every six hours. The live migration map in the right vertical shows the direction of many thousands, if not millions, of migrants in near real-time.

How to use the maps

birdcast forecast map
Cornell University's migration forecasts show predicted nocturnal migration three hours after local sunset and are updated every six hours. Birdcast Project

"The heart of understanding the site is pairing the live map with the forecasts maps," said Horton. It’s not realistic for even the most serious bird-watchers to be outside watching birds all the time, and because migrants may be there one day and gone the next, using the maps in conjunction with each other can help people plan when to prioritize and maximize their bird-watching opportunities.

"If you can see a forecast that shows that three days out it is supposed to be great conditions for migratory birds arriving, you can schedule around that," Horton said. "If, for example, you know on Thursday that Saturday is setting up to be a great night for migration, you could validate this Saturday night by looking at the live migration map. If things are developing as predicted, that’s likely to be a great time to observe some of these birds as they make landfall in your surrounding area." There’s also an online guide about how to use the migration forecast tools.

Serious and casual bird-watchers alike can take their observations a step further and assume the role of citizen scientists.

"From the ornithology side of things, we don’t know from the radar the species that are flying on a given night," Horton said. "So, we encourage everyone to submit their observations to eBird, an online repository for bird-watching observations run by the Cornell Lab of Ornithology. Each year thousands of observers submit millions of observations from around the world. This massive volume of data has been used, and continues to be used, for great conservation science. We hope our forecasts and live updates can serve as an extra motivator to get out and collect more data."

Most birds migrate at night

tanger migratory bird
The scarlet tanager tends to spend winter in the tropical rainforest near the Andes. Kyle Horton

Something that may come as a surprise to casual bird-watchers is that the BirdCast site measures and forecasts migration at night. "It’s probably not widely known that a tremendous volume and diversity of birds move at night," Horton said.

There are some simple reasons for that. Birds of prey — for example, red-tailed hawks, ospreys, peregrine falcons — migrate during the day when these large-winged birds can ride on thermal heat columns.

"As the sun begins to rise, the surface of the Earth starts to heat and causes upwellings of air into the atmosphere," Horton explained. "Raptors can localize these pockets of rising air and efficiently migrate on those. But a lot of the smaller-bodied birds really can’t employ that strategy. So, they move at night when it is much cooler and the winds are calmer. There are hundreds of species that are moving under the cover of darkness. These include the warblers, sparrows, thrushes, tanagers, grosbeaks, flycatchers and vireos."

Migration activity peaks earlier in southern latitudes during the spring. The Gulf of Mexico region typically peaks around the third week of April. Going northward, peak migration in states like New York and Michigan is likely to occur around the first and second weeks of May. People in some parts of the country, such as the Rocky Mountain states, will never see the heavy concentration of migrants as people in states in the Central and Eastern flyways do. But, Horton emphasized, for bird-watchers in these less-traveled areas, migration is relative. It’s happening in these areas, just not at the same intensity as in other places.

A thrush eats berries on a tree
People who live along the path of migratory birds, such as this thrush, can help them by using plants that produce fruit in the autumn. Bachkova Natalia/Shutterstock

Then in early-to-mid August, the fall songbird migration will start ramping up again. In mid-September, Horton said bird-watchers can start looking for large waves of birds to begin coming through their areas with that peak continuing until about mid-October.

This clockwise migration, called a loop migration, is driven largely by the wind patterns in North America and the Western Hemisphere. Because the birds will have bred during the summer, there will be more migrants on the fall journey than the spring migration. They will also be coming through long urbanized stretches where the light pollution will be far worse than in the Great Plains of the Central Flyway. The flocks will also be more susceptible to artificial light disorientation because there will be so many young birds that have no experience in migration.

"The impact of light on them might be that much higher because it is such a novel stimulus and may cause a sort of enhanced disorientation," Horton said.

What's best time of day to observe migrating birds?

migration birds
The Baltimore oriole is a migratory breeding bird known for its whistling songs. Kyle Horton

Knowing in advance what days the birds will be arriving is half the battle, but that leads to new question: What's the best time of day to observe them?

That can vary depending on where you are in the country but, generally, Horton said the sweet spot is the first two hours after the sun rises. "It’s a phenomenal time to see these birds," he said. "Many of them will be quite active because they have flown all night and are trying to build up their fat stores. So, they are actively foraging and very often singing. It is an exciting time to get out and hear the diversity of bird songs."

But, Horton added, if you can’t be out that early, don’t get discouraged. The migrants will generally stick around for the day. Then, as conditions become suitable later in the day, they will take off again to continue their journey. And don’t despair if you miss one group of arrivals altogether. New waves will move in each morning.

Practical uses for the data

Cornell birdcast live map
Real-time analysis maps show intensities of actual bird migration as detected by the U.S. weather surveillance radar network. Birdcast Project

Cornell scientists ultimately hope these data will be used to reduce the mortality of birds during peak migratory seasons. Horton hopes the data will help researchers talk with municipalities, energy producers and homeowners about, among other things, disorientation caused by nighttime light pollution, collisions with structures such as buildings and wind turbines plus predation from cats. "We’ve never had this data available before, so everything is quite new at this point, and we’re in the infancy of having this conversation," Horton said.

A key place to begin that conversation is the Central Flyway of Texas and Oklahoma through Kansas, which is an important flyway for migrant birds with literally billions of them coming through during the spring migration. After their 500-mile journey from places like the Yucatan Peninsula across the Gulf of Mexico, the birds first must deal with the disorientation that can be caused by light pollution in heavily populated cities such as Houston, San Antonio, Austin and Dallas.

"We have broadcast the arrival of migration forecasts and live migration maps on social media. It’s very encouraging that organizations like Houston Audubon are seeing the conservation utility of the data, notifying followers that migrants are on their way and to turn off outside lights when possible," Horton said.

Another goal is to link efforts to reduce light pollution with other conservation actions such as trying to mitigate bird mortality from collisions with wind turbines. No sooner have the waves of birds navigated their way through cities on their way north to their breeding grounds than they encounter these huge clean-energy generators — and that can be fatal for the birds.

"We wouldn’t expect any wind facility to turn off their turbines for all of spring or fall migration," said Horton. The goal, rather, is to provide data that identifies the days and times large volumes of migrants are going to move through. Then, scientists can alert energy facilities and ask them to turn off their wind turbines during those times.

Wind turbines, Horton pointed out, are not the largest driver of mortality for migrating birds. In fact, they are far from it. More pressing issues include habitat change, degradation and loss and cat predation, which Horton said is a huge issue for migratory birds.

The estimated annual mortality figures for birds are staggering. According to data provided by Scott R. Loss, assistant professor of Global Change Ecology and Management in the Department of Natural Resource Ecology and Management at Oklahoma State University, the annual median estimates (the average of high and low estimates) for bird deaths from various causes in the U.S. are: cats, 2.4 billion; building windows (residential and non-residential), 599 million; automobiles, 199.6 million; power line collisions, 22.8 million; communication towers, 6.6 million; power line electrocutions, 5.6 million; and wind turbines, 234,000. The lowest estimate for accidental bird deaths is more than a billion and the upper estimate is around 5 billion, according to estimates Loss provided.

You can do your part to help them by tracking their arrivals on BirdCast, turning off outdoor lights, stocking feeders, and keeping cats indoors.