TORONTO – In groundbreaking research, Canadian scientists have for the first time tracked the flight paths of migrating songbirds by fitting them with tiny geolocators carried in miniature backpacks.
“Never before has anyone been able to track songbirds
for their entire migratory trip,” said lead investigator Bridget
Stutchbury, a professor of biology at Toronto’s York University.
“One
aspect of the research is looking at really this miracle of migration
and how these little birds are able to make these long trips,”
Stutchbury said. “And these geolocators allow us for the first time to
do a start-to-finish map.”
Songbirds
fly thousands of kilometres to and from their breeding and wintering
grounds during the annual migration. But existing technologies like
radio-frequency or satellite-tracking weren’t suitable for tracking
birds small enough to fit in the palm of a hand.
Stutchbury’s
team worked with the British Antarctic Survey to design a miniaturized
geolocator – weighing less than a dime – that could be easily carried
on the backs of songbirds in order to chart their migration routes and wintering destinations.
The
research began in summer 2007, when the team captured 14 wood thrushes
and 20 purple martins at their breeding grounds in Pennsylvania, then
strapped on the geolocators before the birds took wing for Central and
South America.
The devices are mounted on the birds’ backs by
looping thin straps around their legs. The geolocator rests at the base
of the bird’s spine to avoid interfering with its balance.
“We
know that birds wearing geolocators have successfully mated and laid
eggs … and were able to find food and feed their young,” Stutchbury
said in a teleconference arranged by the National Geographic Society.
“Our observations showed that these birds were not slowed down or
showed any signs of even knowing they were carrying a backpack.”
Unlike
global positioning systems that use satellites to pinpoint the location
and movement of a vehicle, for instance, geolocators have an onboard
sensor that records light levels at sunrise and sunset.
And
since the times of sun-up and sunset are known for any given day
anywhere on the planet, Stutchbury said, “we can match up the sunrise
and sunset times to the location where that bird must have been on that
day.”
When bird flocks returned last spring, the scientists were
able to retrieve geolocators from five wood thrushes and two purple
martins and analyze the data to map individual migration routes and
wintering locations.
What they found was a surprise, say the researchers, whose report is published in this week’s issue of the journal Science.
The data showed that songbirds can fly more than 500 kilometres in a single day, far more than the 150 kilometres per day that previous studies had estimated.
What’s more, the researchers discovered that songbirds‘
migration rate was two to six times faster when they headed north in
the spring – to breed – compared with their southerly trip in fall. For
example, one purple martin took 43 days to reach Brazil during fall
migration, but in spring returned to its breeding colony in just 13
days.
“So this bird was able to fly over 7,000 kilometres in under two weeks,” she said. “It’s really stunning.”
But the research isn’t only about charting migration routes – it’s also about species conservation, Stutchbury said.
Wood
thrush numbers have declined by about 30 per cent since the mid-1960s,
just one example of how songbird populations worldwide have plummeted
over the last 30 to 40 years.
“They’re in such a tailspin that
there’s a real sense of urgency to use geolocators to try to identify
what’s causing the problems,” said Stutchbury, adding that scientists
need to understand whether changes in habitat in either the breeding or
wintering grounds are “driving the numbers down.”
Ryan Norris, a
biologist at Ontario’s University of Guelph who studies migratory
animals, said the successful use of geolocators should have “a
significant impact” on future songbird research.
“Up until now,
the ability to track animals over large distances has really relied on
rough estimations,” said Norris, who was not involved in the study.
“Geolocators look to be more accurate.”
While the research shows that individual songbirds
can be tracked using the devices, he said the challenge is to map
migratory pathways across the entire range of a single species.
“So
the next question is where do the other breeding populations winter? Do
they mix with the Pennsylvania population or do they winter in another
separate area?” he said. “And that’s important for conservation
decisions and how to allocate resources for conservation.”
