For decades, the closest that scientists ever came to studying the migration patterns of songbirds was to stalk them for a few days at a time in a small aircraft.
Today, thanks to the efforts of a Canadian biologist and a bird-sized, data-gathering "backpack," researchers have for the first time an accurate measurement of how quickly purple martins and wood thrushes travel south for the winter and back north to breed.
Turns out, it's ridiculously quickly.
Data gathered by York University biologist Bridget Stutchbury shows that some songbirds make it back from the Amazon basin to their northern U.S. breeding grounds in just two weeks. Based on the best available data, scientists had guessed the trip would take about a month.
The study marks the first time anyone has mapped songbird migration routes to the tropics and back.
"It's completely changed the way we look at these little birds and what we're capable of," Prof. Stutchbury said.
In a paper to be published in Science magazine, Prof. Stutchbury describes a new technique that allowed her to monitor two species of songbirds continuously. Researchers captured birds in their northern U.S. breeding grounds in late summer and attached to them tiny geolocator "backpacks." The devices, which weigh about as much as a dime, are attached to the birds' legs using teflon straps so as to not interfere with wing movement.
The geolocators record sunrise and sunset times. When the birds are recaptured after their return from the south in spring, the data is downloaded and compared to listings of sunrise and sunset times across the region, allowing scientists to map out the journey.
Before the use of geolocators, researchers used radio transmitters to track bird migrations. However that required constant proximity to the signal. Prof. Stutchbury said the best previous data she had came from a researcher who followed the birds in a plane for about four days -- in 1973.
"We expected [the birds' travel time would be]about a month," she said. "Based on other studies, we had little glimpses of what these birds can do."
But only the slowest bird recaptured - a wood thrush that eschewed a perilous 12-hour non-stop flight across open water for a safer route - took a month to get back. Some of the other birds took half as long, beating by a wide margin researcher estimates of about 150 kilometres a day.
Prof. Stutchbury chose the two species because of their vastly different migration habits. Wood thrushes tend to travel to central America and fly at night, whereas purple martins travel further south, and fly during the day.
For songbirds, there are significant advantages to arriving back north as early as possible, including claiming the best breeding spots and most desirable mates.
Prof. Stutchbury said she hopes to use the newly collected data to study how habitat quality affects the birds' ability to make these trips, and whether it's the winter or the breeding grounds that have the biggest impact.
That information could prove vital to the conservation of songbirds, whose numbers have plummeted. In North America alone, Prof. Stutchbury said, there are some 30 species showing long-term decline.
THE BIRDS
The wood thrush is renown for having one of the most beautiful songs of any North American bird. The birds tend to winter in Mexico and other parts of Central America. As such, the birds' flight path sometimes includes a perilous 14-hour non-stop flight over the open waters of the Gulf of Mexico, which results in certain deaths for birds that can't make the trip in one go.
Wood thrushes tend to stick to forested areas, and fly at night. Despite their numbers dropping significantly over the past few decades, the birds are still considered a relatively less urgent conservation challenge, compared to other species.
Purple martins are North America's largest swallow, measuring about 20 centimetres in length. Unlike wood thrushes, purple martins tend to travel further south to the Amazon basin for the winter. The birds tend to travel in large flocks.
Purple martins are known for their aerial acrobatics, and tend to feed on insects out in open areas. The bird's call is a distinctive, loud noise. The combination of its distinctive sound and dazzling flight have the made purple martins a favourite of bird lovers.