Songbird secrets

Songbird secrets

Promiscuity, divorce and speedy migration are all part of the life of a songbird
September 1, 2010

Talk about getting a bad rap. In the extensive scientific literature about songbirds, the purple martin has long been described as a leisurely migrant that takes its time each fall flying from breeding grounds in Canada and the northern United States to its winter home in Brazil or elsewhere in South America. But in fact, this charming and colourful member of the swallow family flies an impressive 400 to 500 kilometres a day until it reaches Central America. Then it makes a two-week pit stop to regain its strength before resuming the journey at the same blistering pace.

And many other migratory songbirds travel at equally extraordinary speeds, according to groundbreaking fieldwork by York University biologist Bridget Stutchbury. A Canada Research Chair in Ecology and Conservation Biology, Stutchbury has published her findings in many scientific journals as well as a book released last spring, The Bird Detective: Investigating the Secret Lives of Birds, which has become a national best-seller.

Stutchbury has made some startling discoveries about the sex lives of the birds that embellish our fields, forests and backyards with their brilliant colours and melodious songs. Divorce, adultery and betrayal, for example, are commonplace. Females are frequently unfaithful to their partners and will dump one male for another that is stronger, healthier and blessed with brighter plumage or a more robust singing voice.

But such fickle behaviour has nothing to do with emotional flakiness. It’s all about survival of the species.

“They’re trying to gauge genetic qualities,” says Stutchbury. “They’re looking for high-quality males in order to produce high-quality offspring.”

Stutchbury conducts most of her field studies in the hilly, heavily forested and songbird-rich tip of northern Pennsylvania bordering Lake Erie. And there is nothing remotely voyeuristic about her research into avian sexual behaviour. She begins by erecting a device called a mist net, which resembles a gigantic, rectangular non-stick spiderweb, 12 metres long and 3 metres wide. Birds that fly into the net are captured, and Stutchbury extracts a few drops of blood from their wings. The samples are then analyzed to identify each bird’s father.

The net is also the starting point for Stutchbury’s studies of migratory behaviour. She attaches a tiny geolocator to the back of each captive bird. The battery-powered electronic device is roughly the size of a dime and weighs about 1 to 1.5 grams. A sensor records light levels 24 hours a day, and this information is used to determine where a bird is at sunrise and sunset each day.

Stutchbury was the first scientist in the world to use a geolocator in research involving songbirds. The British Antarctic Survey (BAS) developed the gadget over a decade ago to track the migrations of geese and albatrosses, but it was too large to be attached to a songbird. Stutchbury worked with the BAS to produce a smaller version, which led her to a discovery that has completely disproved the conventional thinking about the speed of songbird migrations.

Stutchbury’s findings were published in the journal Science in 2009, and since then, dozens of researchers around the world have begun using geolocators.

“It’s led to a revolution in the study of birds,” says Stutchbury. “The next year or two is going to rewrite what we know about migration.”

Equally important, the results may answer some perplexing and troubling questions. Stutchbury notes that a number of species with summer breeding grounds in various parts of Canada are in serious decline and are listed as endangered or are even facing extinction. In many cases, Canadian habitat is plentiful and the birds are producing healthy offspring.

“There are no obvious problems with their breeding grounds,” she says. “Something is happening during migration to their wintering grounds. Unless we know where they’re going, there’s no hope of solving the problem.”

Stutchbury and others who are concerned with the health of bird populations will be holding their collective breath when the annual southerly migration begins this fall. They are deeply concerned about the impact of the BP oil spill and the resulting contamination in the Gulf of Mexico. She notes that the Mississippi Delta is part of an avian superhighway over which dozens of species fly each year as part of their journey across the Gulf to Mexico.

“We’ve never had a spill that big, and it couldn’t have happened in a worse location,” says Stutchbury. “Songbirds from the boreal forest of Canada fly over there and use it as a stopover. We don’t know whether they’ll be harmed by the contamination.”