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Pairs of migratory birds work well long distance

Scientists are astonished by how well pairs of a species of Icelandic migratory birds know exactly when to return home to breed after they spend winters in different countries.
/ Source: Reuters

They rarely see each other, spend winters in different countries and don’t communicate for long periods but pairs of a species of Icelandic migratory birds know exactly when to return home to breed.

The couples of black-tailed godwits somehow manage to coordinate their journeys, from different countries up to 1,000 km apart, to arrive back at their Iceland breeding grounds within about three days of each other.

“When males and females from a pair arrive back on their breeding territory in the spring, they do so with remarkable synchrony,” Jill Gill, of the University of East Anglia said in an interview.

“We’re astonished by it.”

Scientists had assumed that males and females of migratory bird species stayed together during the winter and traveled back with each other to their breeding grounds.

“In this particular species, the males and females are going to completely different locations, often different countries, so they are wintering on average 1,000 miles apart,” said Gill, who reported the findings in the science journal Nature.

“And yet they are getting back somehow to the breeding ground within two or three days of one another.”

It takes about a month for the entire population of godwits, which stand about 8 inches (20 cm) tall and weigh roughly 10 ounces (300 grams), to get back to Iceland from their wintering spots dotted around Europe.

Cases of divorce
Couples manage to time it with extraordinary accuracy but if one of them gets it wrong, their partner takes up with another male or female.

“We have had two cases of divorce,” said Gill. “In both cases the female got back before the male.”

Tired of waiting, both females mated with other males.

Gill and her colleagues discovered the unusual talent of the Icelandic black-tailed godwits with the help of a huge network of birdwatchers throughout Europe.

Researchers tagged the birds and volunteers took note of when the godwits arrived and left.

“We get hundreds of sightings from people right across Europe so we are able to work on a large scale,” said Gill.

But she and her team are perplexed about how the birds get it right.

“We know they don’t meet up in the wintering grounds and they don’t meet up on passage. The first time they see each other is when they arrive on the territory,” Gill said.

“Our suspicion is that what we see in the godwits may be true for many other species as well.”