Fall migration maps reveal where birds fly over North America

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If you’re like me, you’ve probably had enough of the weather forecast. It’s often wrong or shows me what I don’t want to see.

I’m here to tell you that there is a better forecast, a forecast for birds.

Called BirdCast, the forecast provides a three-day forecast of how many birds will fly over the country – and where. After sundown on Tuesday, for example, BirdCast estimates that 74,000 of them will travel across New York City skies. The tool, which was developed by the Cornell Lab of Ornithology and a handful of other universities, also shows where large numbers of birds navigate in the sky. in near real time. In other words: it’s radar, but for birds.

This type of predictive technology is particularly useful as fall migration approaches its peak in North America. Each fall, billions of migratory birds travel south in search of food and warmer weather, some traveling several thousand kilometers. The famous arctic tern takes an epic journey of more than 12,000 miles from the Arctic to the Antarctic, a distance that exceeds the longest non-stop commercial flight in the world.

Migration offers a sort of fleeting paradise, even for novice bird watchers. You can see all kinds of unique species in your backyard as they pass, like warblers, thrushes, and sparrows in New York’s Central Park. Forecast maps like BirdCast help in revealing migration hotspots from southern Texas to the Great Lakes region.

These tools are also a boon to birds. Hundreds of millions of them die each year from collisions with windows, and disorienting lights are a big part of the problem. Forecasts can help cities determine when to turn off lights, allowing more winged passers-by to pass safely.

The Field Museum in Chicago has collected tens of thousands of birds that collided with buildings downtown. These four are from his collection.
Courtesy of the Field Museum

See where the birds fly above

Our ability to map and predict birds is rooted, like so many innovations, in warfare. Engineers developed radar technology during WWII to detect enemy planes, which essentially involves broadcasting microwaves and seeing what they bounce off – much like a bat might use sonar. to map a dark cave. During the war, radar operators began to notice strange spots – known as “angels”- appearing on their screens. The operators, some of whom were bird watchers, eventually figured out that the points were not bomb-carrying planes at all. They were birds.

The discovery sparked a revolution in ornithology. For the next eight decades, scientists used radar technology to detect birds and insect swarms in the night sky, just as meteorologists did. used to map hurricanes and torrential rains. More recently, major advances in computer science have made it easier to process large amounts of data, allowing scientists to make detailed migration predictions over a short period of time, said Andrew Farnsworth, senior associate researcher at the Cornell Lab of Ornithology, who heads the BirdCast. project. We are now in the era of radar ornithology, he said.


BirdCast’s live map shows where the birds migrate. Warmer colors indicate that more birds are passing through an area.
Van Doren and Horton / BirdCast

First launched in 2000, BirdCast runs on software that analyzes weather radar to discern what a bird is in relation to a cloud or other object. This analysis produces a map of the United States that shows where birds migrate in the sky, like the one above, with warmer (more orange) regions showing where there is more bird traffic, that is ie more birds moving in an area at any given time. Pretty neat, isn’t it?

BirdCast also produces a three-day forecast, which estimates nocturnal movements, as the vast majority of North American birds migrate after dark. Researchers have a good idea of ​​how the weather affects their movements – temperature, which affects wind speed and direction, is especially important in determining when birds are traveling, Farnsworth said. By taking advantage of the weather forecast, BirdCast estimates where birds might migrate in the near future. (You can find “live” migration forecasts and maps here.)

BirdCast migration forecast for Thursday, September 30.
Van Doren and Horton / BirdCast

You can use these maps for bird watching, but keep in mind that they show the number of birds in the sky – not on the ground – and the forecast is for nighttime migration. Where predictive power really comes into play is to help cities, young and old, reduce the number of birds that die crashing into buildings.

How bird forecasts can reduce window collisions

Every year in the United States, between 365 million and 988 million birds die while running in buildings, researchers say estimate. It is the second leading killer of birds in North America after predation by domestic cats, and light pollution is a big part of the problem. Lights can attract and disorient birds, causing them to crash.

This is what makes bird forecasts so useful: when we know that a large number of birds are about to pass through a particular region, it is clear that we can prevent strikes by turning off at least some of the birds. lights of buildings at night. It really is that simple – and we know it works.

A study published this summer, for example, they found that halving the area of ​​lighted windows in a large Chicago convention center during spring migration resulted in 11 times fewer collisions. The authors further concluded that dimming the lights during migration could reduce the number of collisions in the center by about 60%. You rarely encounter conservation victories of this magnitude – and literally overnight, moreover.

BirdCast has a characteristic Called “lights out alerts,” which reveal which cities should prioritize lights out and when.
Van Doren and Horton / BirdCast

In the United States, more than 40 cities now have Lights Out Programs, and some, including New-York, They succeeded legislation require buildings to be more bird-friendly, for example by using glass with patterns that make windows more visible to birds. BirdCast, for its part, has a characteristic called “extinction alerts” (pictured above) which can help cities determine when to darken.

Likewise, researchers have proposed using forecasts to help reduce bird strikes at airports, which cause over a billion dollars of damage every year in the world. In a A recent study, scientists analyzed airplane-bird collisions at three New York City airports and found that weather radar can “accurately predict the likelihood of bird strikes.” Theoretically, airports could use this information to make flights safer and cheaper.

What the radar reveals about birds

Bird radar is not only useful for bird watchers and collision prevention. It also helps scientists answer some of ornithology’s biggest questions, such as how climate change affects the timing of migration.

Radar results 2019 to study, for example, found that rising temperatures alter spring migration about two days earlier per decade in the United States, on average. (The changes are much larger as you move further north.) It might not seem like much, but migrations are carefully planned events where timing is a matter of life and death.

Birds have adapted to arrive at particular places at particular times – for example, “when the pulses of spring insect flowers peak,” Farnsworth said. “With temperatures rising earlier, birds can arrive after the pulse of food availability, creating an increasing mismatch. If this happens quickly, bird populations might not be able to keep up. ”

Researchers are also using radar to take a closer look at some of the unknowns of migration, such as what happens to birds during a heavy thunderstorm or when wind patterns suddenly change. They previously thought storms could put an end to migration, Farnsworth said, but radar suggests otherwise. “The idea that rain automatically stops migration is totally wrong,” he said. “Birds move in all kinds of conditions. “

Yet despite all the advances in radar ornithology, one major mystery remains largely unsolved. How? ‘Or’ What to do birds sail, anyway? I’ve always been back to my hometown, so it’s hard to imagine birds could travel thousands of miles to a destination they’ve never seen or visited. To achieve such a feat, they probably use a combination of the sun, stars, Earth’s magnetic field, and maybe even their sense of smell. But exactly how they put all this information together to navigate is “a total mystery,” Farnsworth said. “I don’t think we’re starting to figure it out.”


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