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These high-tech tools study the ancient migratory routes of birds

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While it still feels like beach weather in much of North America, billions of birds have started flying for one of nature’s great spectacles: autumn migration. Birds fly south from the northern US and Canada to wintering grounds in the southern US, the Caribbean, and Latin America, sometimes spanning thousands of miles. Other birds leave temperate Eurasia to Africa, tropical Asia or Australia.

Using observation records and data collected through bird banding20th-century ornithologists roughly mapped general migration routes and timing for most migratory species. Later, using radar at airports and weather stations, they discovered how weather and other factors affect when birds migrate and how high they fly.

Today, technological developments provide new insights into bird migration and show that it is more complex and miraculous than scientists ever imagined. These new and continuously improving technologies are important tools to protect migratory birds from: habitat loss and other threats.

Birds across the border

The power of the internet has greatly aided research on migratory birds. Using the popular eBird Networkcan bird watchers around the world upload observations to a central database, creating a real-time record of the ebb and flow of migration. Ornithologists have also learned to use NEXRADa national network of Doppler weather radars, to visualize birds that migrate across the North American continent.

Now scientists are setting up a global network of receiving stations called the Motus Network, which currently: 1,500 recipients in 31 countries. Each receiver constantly records the presence of birds or other animals within a nine-mile radius that scientists have equipped with small, lightweight radio transmitters, and shares the data online. The network will become increasingly useful for understanding bird migration as more receiving stations along migratory routes become active.

Track individual birds via satellite

Three new technologies are rapidly expanding what we know about bird migration. The first is satellite telemetry of bird movements. Researchers fit birds with tiny solar-powered transmitters, which send data about the birds’ locations to a satellite and then to a scientist’s office computer. The scientist can learn where a bird is, the route it takes to get there and how fast it travels.

For example the black-tailed godwit, a shorebird the size of a dove, breeds in Alaska and then migrates to New Zealand. Satellite channels show that black-tailed godwits often fly non-stop from Alaska to New Zealand. Recently, a black-tailed godwit set the record for the longest non-stop flight by a land bird: 8,100 miles in 10 days, from Alaska to Australia.

Satellite telemetry surveys show how much individual birds, even those from the same breeding site, vary in their migratory behavior. Individual differences in migratory behavior are likely due to differences in physical condition, learning, experience and personal preferences.

Another shorebird, the whimbrel, also makes a phenomenally long journey across the ocean. Satellite telemetry has shown that some whimbrels travel from northwest Canada across the North American continent to Canada’s east coast, then take off across the Atlantic for a six-day nonstop 3,400-mile flight to the coast of Brazil. In total they are allowed to travel 6,800 miles.

Unfortunately, hunters kill some of these birds when they land to rest on islands in the Lesser Antilles. The unfortunate fate of two satellite-tracked whimbrels has catalyzed a campaign to tighten regulations hunting shorebirds in the Caribbean.

Geotagging small birds

Many birds are too small to carry a satellite transmitter. Given the energetic effort required for migration, a device must weigh less than 5% of a bird’s body weight, and many migratory songbirds weigh less than 0.7 grams.

An ingenious solution for small birds is a geolocator tag or geologger—a small device that just records time, location and presence or absence of sunlight. Scientists know the timing of sunrise and sunset on a particular date, so they can calculate the location of a bird on that date to within about 200 miles.

Birds carrying geologgers must be recaptured to download the data. That means the bird has to survive a migration tour and return to the same place where it was first captured and tagged. Amazingly, many small birds with a geologger do just that.

Geologgers have shown that black-headed singers– small songbirds that breed in the boreal forests of North America – fly long distances across the Atlantic in the fall, heading for the Amazon basin. Birds that breed in eastern North America migrate across the Atlantic into maritime Canada or the northeastern United States and make a 60 hours, non-stop, 1500 miles flight to the Greater Antilles. There they rest and recuperate before continuing across the Caribbean to South America.

Blackpolls breed in Alaska flying over the North American continent before leaving shore on the Atlantic coast and fly to South America. In total they cover 6600 miles in 60 days.

Even more astonishing: geologgers show that another small passerine bird, the wheatear, migrates from North America to sub-Saharan Africa. Wheatears breeding in Alaska fly 9,100 miles across Asia to East Africa, taking three months. The animals that breed in eastern Canada travel 4,600 miles across the Atlantic to Europe and then to West Africa – including a 2100-mile, four-day, non-stop flight over water.

Record Night Migratory Calls from Birds

Two hours after sunset in the fall, I like to sit outside and listen to birds migrating over my head. Most birds migrate at night, and many give a species-specific “chit”, “soap” or other call in flight. The calls can serve to keep migrating flocks together, including: different species on their way to the same destination.

Using Ornithologists automated passive acoustic recording to study these nocturnal calls and identify the species or group of related species that make each noise. The technology is a microphone that faces the sky, is connected to a computer that continuously records the sound stream, and is supported by sound recognition software. Sometimes it reveals migrants overhead that are rarely seen on the ground.

Nick Kachala, an honors student in my lab, set up recording units in three university buildings in the fall of 2021. One of the most registered migrants was the gray-cheeked thrush, a shy northern boreal forest bird rarely seen in the northeastern United States during its fall migration. He also discovered the dickcissela grassland bird that I have never seen in our area.

Many bird watchers are now building DIY backyard recording units to identify the birds that fly over their homes during migration.

Protecting Migratory Birds

Radar monitoring indicates that the number of North American migratory birds decreased by 14% between 2007 and 2017. There are likely multiple causes, but habitat loss is probably the main culprit.

Satellite telemetry and geologgers show that along migration routes there are special stops where migrants rest and refuel, such as the coast of the Gulf of Texas, the Florida Panhandle, and Mexico’s Yucatan Peninsula. Conservation experts generally agree that protecting migratory birds is critical save these sites.

Effective conservation measures require you to know where and how birds migrate and the dangers they face during migration. Ornithologists using these new technologies are learning things that help stop and reverse the global decline in migratory birds.


Tom Langen is a professor of biology at Clarkson University.

This article was republished from The conversation under a Creative Commons license. Read the original article.


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