“Ottawa” Science of Spring: Songbirds now Report their Location as they Fly
Automation has come to the world of biologists who study bird migration, taking away some of the hard labour involved in studying tiny creatures that live in treetops.
This is a happy change for York University’s Bridget Stutchbury, who has chased songbirds through forest canopies for decades.
In the old days, she would put a tiny geolocator on a bird — a device that recorded where it went. The drawback: She would send birds south with these tiny backpacks, but she had to catch them again the next spring to extract the data. That meant putting out nearly invisible nets and waiting for the bird to fly into one.
“Sometimes we would have a bird and we could see the tag (geolocator) on it but just couldn’t catch the damn thing.”
Today, lines of detectors on towers sit passively, waiting for the migration of little birds with chips tied on little backpacks. The network is called Motus, and it has receivers scattered from Eastern Canada to Central America. In Canada, they are concentrated in southwestern Ontario, Nova Scotia and along the St. Lawrence River.
“If it flies near a tower, it goes Ping! and you know that your animal was near the tower. It’s ideal for studying migration,” Stutchbury said.
A new line of towers across Panama records passing hawks, which stay over land because they ride on “thermals,” or air that rises over warm land. (Little songbirds often cross the Gulf of Mexico. It’s a shorter route.)
There are more arrays of these bird detectors in Florida, and in southwestern Ontario where birds cross Lake Erie.
“It’s quite impressive how many are picked up by these towers,” she said.
It’s like the Distance Early Warning lines of radar stations that were set up in the Cold War to detect Soviet bombers coming across the Arctic, she notes, “though with a friendlier purpose.”
Biologists have been able to watch other wildlife at a comfortable distance for years. Wolves carry radio collars, and no one has to go near the wolf to unload data. The same goes for sharks, whales and more.
But songbirds are tiny — about 10 to 30 grams, depending on the species. That means most weigh less than an ounce.
“So they’re too small to carry conventional tags,” Stutchbury said. “They have to make these things really tiny, and they have finally been able to do it.”
Another key is battery life. Batteries lasted three weeks when she got into the tracking business around 1990; today they last more than a year, enabling the biologist to follow an individual bird south in fall and then north again.
That brings her to wood thrushes, a species at risk in Ontario. Cute little brown bird, lovely song.
The young birds leave the nest and never return to that same territory, which leaves a conservation riddle. Where do they go?
“We’re trying to understand juvenile survival. … We have no idea how many of the kids that are produced every year actually return to breed, because they don’t return home,” she said.
She puts tiny tracking devices on them, and with the long-life battery she can watch them first exploring new territory far from the nest in late summer, and then going south and coming north again.
“We have never been able to track juveniles before.” She expects the youngsters will fly around Lake Erie while their experienced parents go straight across the water, but this spring’s data will show for certain.
Migration remains a wonder to Stutchbury: Tiny birds travelling thousands of kilometres, sometimes flying non-stop day after day.
“They’re running back-to-back marathons. Something like the blackpoll warbler can double its body weight in a week (before migration), and burn it off in three days.”
Stutchbury has a Canada Research Chair in ecology and conservation biology.