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Although it still looks like coastal weather for most of North America, billions of birds are beginning to take to the wings for one of nature’s greatest spectacles, the fall migration. Birds fly from North America and Canada to their wintering grounds in South America, the Caribbean and Latin America, sometimes covering thousands of miles. Other birds leave central Eurasia for Africa, tropical Asia or Australia.
20th century ornithologists used records and data gathered to identify general migration routes and timing for most endemic species. Later, using radar at airports and weather stations, they discovered how much weather and other conditions affect birds’ migration and how far they fly.
Today, technological advances are providing new insights into bird migration and revealing that it is more complex and fascinating than scientists thought. These new and ever-evolving technologies are key to protecting migratory birds from habitat loss and other threats.
Bird crossing the border
The power of the Internet has greatly aided migratory bird research. Using the popular eBird network, you can upload sightings of bird species around the world to a central database, creating a real-time record of the ebb and flow of migration. Ornithologists have also learned to use NEXRAD, a national network of Doppler weather radars, to visualize birds migrating across the North American continent.
Currently, scientists are establishing a global network of receivers called the Motus Network, which has 1,500 receivers in 31 countries. Each receiver continuously records birds or other animals within a nine-mile radius, which scientists attach small radio transmitters to and share the data online. As more receiver stations become active on migration tracks, the network becomes more useful for understanding bird migration.
Welcome to High Migration –@DrBirdCast Over the next 3 nights, >300 million birds are predicted to ascend each. Stay tuned and call local activity in your county on the Migration Dashboard: https://t.co/EayIq61l0A
— Cornell Bird (@CornellBirds) May 5, 2022
Satellite tracking of individual birds
Three new technologies are rapidly expanding what we know about bird migration. The first was satellite telemetry of bird movements. Researchers attach the birds to small solar-powered transmitters that transmit the birds’ location to a satellite and then to a computer in the scientist’s office. The scientist can figure out where a bird is, the path it took to get there, and how fast it is traveling.
For example, the bar-tailed godwit, a pigeon-sized shorebird, breeds in Alaska and then migrates to New Zealand. Satellite transmitters show that godwits regularly fly from Alaska to New Zealand. Recently, a godwit set the record for the longest nonstop flight by a terrestrial bird: 8,100 miles in 10 days, from Alaska to Australia.
Satellite telemetry studies show how much individual birds, even from the same breeding grounds, differ in their migratory behavior. Individual differences in migration behavior are probably due to differences in physical condition, education, experience, and personal preferences.
Another seabird, the wimberle, also makes surprisingly long journeys across the ocean. Satellite telemetry showed that some of the whips traveled from northwest Canada, across the North American continent to Canada’s east coast, before making a 3,400-mile, six-day nonstop flight to the coast of Brazil. They can travel a total of 6,800 miles.
Unfortunately, hunters kill some of these birds when they come to roost on the islands of the Lesser Antilles. The fate of two satellite-tracked wimberles has fueled a campaign to tighten regulations on coastal hunting in the Caribbean.
Geographical small birds
Many birds are too small to carry a satellite dish. Due to the strenuous effort required for migration, gear should weigh less than 5% of the bird’s body weight, and many migratory songbirds weigh less than 0.7 ounces.
A great solution for small birds is a geolocator tag or geologger—a small device that simply records time, location, and the presence or absence of sunlight. Because scientists know the time of sunrise and sunset on a given day, they can calculate a bird’s location to within 125 miles on that day.
Birds with geologgers must be recaptured to download the data. That means the bird must survive the migration and return to the place where it was first captured and tagged. Surprisingly, many geologger-tagged small birds do.
Geologists have shown that blackpoll warblers – small warblers that breed in the boreal forests of North America – fly long distances across the Atlantic Ocean, heading for the Amazon basin. Birds that breed in eastern North America make a 60-hour nonstop 1,500-mile flight to the Greater Antilles, leaving the Atlantic Ocean in Canada or the northeastern United States. They rest and recover there, then continue through the Caribbean to South America.
Blackpolls that breed in Alaska fly across the North American continent before leaving shore on the Atlantic coast and flying to South America. In total, they travel 6,600 miles in 60 days.
Interestingly, another small songbird, the Northern Wheatear, has been shown by geologists to migrate from North America to sub-Saharan Africa. Wheat grown in Alaska flies 9,100 miles across Asia to East Africa, taking three months to do so. Those that breed in eastern Canada travel 4,600 miles across the Atlantic Ocean to Europe and then West Africa—a 2,100-mile, four-day, nonstop flight that includes overwater flight.
Recording the nocturnal migration calls of birds
A couple of hours after sunset in the fall, I like to sit outside and listen to the birds migrating overhead. Most birds migrate at night, and many emit a species-specific “chit,” “zip,” or other call note while in flight. The calls can be used to keep flocks of different species moving together towards the same destination.
Ornithologists are using automated passive acoustic recording to study these nocturnal calls and identify the related species or groups making each call. The technology is a sky-mounted microphone connected to a computer that continuously records the audio stream and is aided by voice recognition software. Sometimes it shows migrants from above that are rarely seen on the ground.
Nick Kachala, an honors student in my lab, set up recording rooms on three university properties in the fall of 2021. One of the most common migrants is the grey-cheeked woodpecker, a shy bird rarely seen in the northern woodlands. Northeastern America during fall migration. He found a grassland bird called Dixisl, which I have never seen in our area.
Many bird watchers are now building do-it-yourself backyard recording units to identify birds flying over their homes during migration.
Protecting migratory birds
Between 2007 and 2017, the number of North American migratory birds declined by 14 percent, according to radar monitoring. There are probably a number of reasons, but the main culprit is habitat loss.
Satellite telemetry and geologists show that there are special stops along migration routes where migrants stop and refuel, such as the Texas Gulf Coast, the Florida Panhandle, and Mexico’s Yucatan Peninsula. Conservationists agree that protecting these areas is critical to protecting migratory birds.
Effective conservation measures require knowledge of where and how birds migrate and what threats they face during migration. Ornithologists are learning how to use these new technologies to help halt and reverse the decline of migratory birds worldwide.
Tom Langen is a professor of biology at Clarkson University.
This article was reprinted from The conversation Under a Creative Commons license. Read the original article.
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