OTTAWA — Tiny songbirds migrate three times faster than anyone suspected, a Toronto scientist has found: from the tropics to Canada and northern U.S. states at speeds up to 577 kilometres a day.
But the bigger news is that Bridget Stutchbury of York University has just revolutionized the way biologists study birds.
“This is the first time anyone in the world has been able to map songbird migration routes to the tropics and back,” she told reporters this week.
Ms. Stutchbury caught wood thrushes and purple martins and strapped tiny “geolocators” on their backs, then released them in the summer.
Tied on with string, the centimetre-long “backpacks” recorded each bird’s travels until spring. Ms. Stutchbury succeeded in catching some of the returning birds (others nested frustratingly out of reach) and retrieved the stored data, based on precise timing of each day’s sunrise and sunset.
“The floodgates are open now” for research into songbird migrations, she said in a conference call with reporters.
That’s vital because while there are billions of little songbirds worldwide, the numbers of many species are in steep decline.
And the birds have been amazingly hard to track. Weather radar often shows large flocks, and banding birds gives some clues to their movement. In 1973, a scientist managed to follow one bird that had a radio collar for four days before losing contact.
But there was nothing beyond these crude tools. Biologists have had to study a bird for half the year, then watch it disappear.
Now all that has changed.
The backpacks weigh about 1.5 grams each, less than a dime; the birds are about 50 g (two ounces). Ms. Stutchbury was worried the backpack might slow the bird down — until she saw how fast they still fly, and watched them catch insects in mid-air.
“These birds (wearing locators) can sneak copulations with each other, they can lay eggs, they can fly to the tropics and back. They are amazing flying machines,” she said.
“The thing that stood out as being so surprising was the really rapid spring migration,” she said. The fall migration was much slower, probably because birds in spring must rush to get the best nesting grounds, but there’s no need to hurry south in fall.
The fastest bird, a female martin, flew 7,500 km in just 13 days from the Amazon jungle to Pennsylvania.
There were other surprises, too small to show up through older study techniques.
Many birds cross the Gulf of Mexico in the rush north, and some fall exhausted into the water and die. But one thrush’s backpack revealed it flew north to the Yucatan Peninsula, and then “slammed on the brakes and took the long way around over land,” along the Gulf shoreline. It arrived late in its nesting ground, hurting its chances of breeding.
The new tracking ability will let scientists find out which birds overwinter in poorer-quality habitat, and see how that affects their return north and their ability to breed the next summer. The effects of forest destruction and pesticide use in Central and South America remain poorly understood because no one has been able to track individual birds in both summer and winter.
The York team’s work is published in the journal Science, and funded by National Geographic.
While martins and wood thrushes were picked partly because they’re large for songbirds, new tracking backpacks are becoming lighter and can fit smaller birds.