Birds Migrate Along Ancient Routes: How Scientists Are Tracking Their Amazing Journeys

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

Using observation records and data collected through bird banding, 20th-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 advances are providing new insights into bird migration and showing that it is more complex and wonderful than scientists ever imagined. These new and constantly improving technologies are key aids for protecting migratory birds in the face of habitat loss and other threats.

Birding across borders

The power of the internet has greatly aided migratory bird research. Using the popular eBird network, birders all over the world can upload sightings 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 down the North American continent.

Now, scientists are setting up a global network of receiver stations called the Motus Network, which currently has 1,500 receivers in 31 countries. Each receiver constantly records the presence of any birds or other animals within a nine-mile (15-kilometer) radius that scientists have fitted with small, lightweight radio transmitters, and shares the data online. The network will become increasingly useful for understanding bird migration as more receiver stations become active along migration tracks.

Tracking individual birds via satellite

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

For example, the bar-tailed godwit, a pigeon-sized shorebird, breeds in Alaska and then migrates to New Zealand. Satellite transmitters show that godwits often fly nonstop from Alaska to New Zealand. Recently, a godwit set the record for the longest nonstop flight by a land bird: 8,100 miles (13,000 kilometers) in 10 days, from Alaska to Australia.

Birding across borders

The power of the internet has greatly aided migratory bird research. Using the popular eBird network, birders all over the world can upload sightings 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 down the North American continent.

Now, scientists are setting up a global network of receiver stations called the Motus Network, which currently has 1,500 receivers in 31 countries. Each receiver constantly records the presence of any birds or other animals within a nine-mile (15-kilometer) radius that scientists have fitted with small, lightweight radio transmitters, and shares the data online. The network will become increasingly useful for understanding bird migration as more receiver stations become active along migration tracks.

Tracking individual birds via satellite

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

For example, the bar-tailed godwit, a pigeon-sized shorebird, breeds in Alaska and then migrates to New Zealand. Satellite transmitters show that godwits often fly nonstop from Alaska to New Zealand. Recently, a godwit set the record for the longest nonstop flight by a land bird: 8,100 miles (13,000 kilometers) in 10 days, from Alaska to Australia.

atellite telemetry and geologgers show that there are special stopover sites along migration routes where migrants rest and refuel, such as the Texas Gulf Coast, the Florida Panhandle and Mexico’s Yucatan Peninsula. Conservation experts widely agree that to protect migratory birds, it is critical to conserve these sites.

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 under 0.7 ounces (20 grams).

An ingenious solution for small birds is a geolocator tag, or geologger – a tiny device that simply records time, location and presence or absence of sunlight. Scientists know the timing of sunrise and sunset on a given date, so they can calculate a bird’s location on that date to within about 125 miles (200 kilometers).

 A painted bunting equipped with a 0.024-ounce (0.7-gram) solar geolocation datalogger. Jeffrey F. Kelly, CC BY-ND 

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

Geologgers have shown that Blackpoll warblers – small songbirds that breed in the boreal forests of North America – fly long distances over the Atlantic in fall, heading to the Amazon basin. Birds breeding in eastern North America head out over the Atlantic in maritime Canada or the northeastern U.S. and make a 60-hour, nonstop, 1,500-mile (2,500-kilometer) flight to the Greater Antilles. There they rest and recuperate, then continue across the Caribbean to South America.