There and back
A look at the miracle of bird migration
Wednesday, Apr 23, 2014 06:00 am
I first knew about a month ago that spring had arrived.
I was out for a walk amongst the still snow-covered fields when I heard the honk of a Canada goose. There it was, standing tall and proud atop a nearby condo complex, presumably complaining about the frozen state of his favourite pool.
Next came the crows, winging their way in from nowhere in their slick new black suits, making a racket. Behind them were the jubilant squeals of the gulls, and the whistling wings of the mallards.
A few predators like the merlin have already landed in town, birder Peter Demulder tells me. The bluebirds should show up any day now.
“From here on, everything comes back,” he said.
It’s migration season, and the birds are coming back. Expect thousands of feathered friends to fill the skies over St. Albert in the coming weeks, each of which is returning home after an epic but poorly understood journey from down under.
Birders such as Demulder and Dan Stoker were out watching for them on the weekend as part of the annual Springing to Life count at Big Lake – a popular stopover for many migratory birds. The count resumes this weekend.
“The migration of birds north is a major sign of spring,” Stoker says.
These birds have come home after travelling huge distances and many local birders such as Stoker like to celebrate their arrival.
Stoker says crows and Canada geese are typically the first birds to return to town, followed by starlings and mallards. Once the lakes thaw, everything else starts to flood in.
Past Springing to Life counts have spotted some 84 different species on and around Big Lake, including tundra swans, Franklin’s gulls and red-winged blackbirds.
“At any given time, you could be looking at 5,000 birds or more,” Stoker said.
There and back again
Chris Guglielmo is the co-director of the Advanced Facility for Avian Research at Ontario’s Western University and has studied migratory birds for about 20 years.
About 80 per cent of Canada’s birds are migratory, in that they leave in the winter and come back for the summer, Guglielmo says.
“It comes down to not enough food and too-harsh winter conditions,” he says.
Many of these birds have tropical ancestors and are ill-equipped to deal with Canada’s winters. Some may feed on bugs, which are tough to find in the snow, or live in open water, which tends not to exist in December. As a result, they fly down to sunny Mexico or South America whenever the weather gets too cold.
But why bother coming back?
“There are all sorts of advantages for birds to come up here,” notes Dick Cannings, who studies migratory birds with Bird Studies Canada.
The north has fewer predators than the south, for example, and longer days in which to feed and breed – 24-hour days in the case of the Arctic, Cannings notes.
Where birds go and when they come back depends on the species, he continues. Some birds just move up or down a mountain range. Many ducks move until they see open water. Most warblers and flycatchers go to Mexico, while Swainson’s hawks fly all the way to Argentina.
Cannings says the Arctic tern racks up the most frequent-flyer miles during migration of any bird, as it breeds in the Arctic and winters in the Antarctic.
“It basically is going around the world,” Cannings said.
If you spot a Franklin’s gull this spring (black head, red beak), you’ll be looking at a bird that’s spent the winter in Chile, Stoker says.
Once here, the gulls will spend their days following combine harvesters by the hundreds, gobbling up any disturbed bugs.
Mysteries of migration
Despite being such a common event, much about migration is still a mystery to humans.
Researchers believe birds know when to migrate by watching for a change in day length – specifically, the change that happens at the winter solstice.
This event triggers radical changes in a bird’s behaviour and body, Guglielmo says. It starts gobbling food and packing on fat, growing its digestive tract so it can eat more at once.
“They become what I like to call these obese super-athletes,” he says, and become physiologically similar to Type-II diabetics – high blood sugar, high insulin resistance, and high fat.
The western sandpiper (which Guglielmo studies) will bulk up to 50 per cent body fat in preparation for migration, he notes as an example. Its heart grows by about 25 per cent, its stomach grows by 50 per cent, and its flight muscles get huge.
“They look like bodybuilders,” Guglielmo says.
Unlike mammals, birds have the proteins and enzymes needed to get about 90 per cent of their muscle power from fat instead of sugar, giving them superhuman endurance, Guglielmo says.
Many birds can fly for two to three days straight without stopping for food, drink or sleep. The bar-tailed godwit (which looks like a big sandpiper) flies for about nine days straight each year to migrate between Alaska and New Zealand – that’s roughly 10,400 kilometres.
“We don’t really know how they do without the sleep,” Guglielmo continues.
Some studies suggest birds can shut off half of their brain at a time, letting one half fly while the other sleeps, he says.
We also know little about how birds know where to go during migration.
Cannings says birds seem to know from birth to head a certain direction for a certain length of time to migrate, allowing them to get to and from their wintering grounds without guidance from their parents.
Experience does play a role when it comes to specific routes, he continues. Take a young bird 500 miles west and it’ll be 500 miles off course when it migrates, for example. Do the same with an adult and it will change course to compensate.
This suggests birds have an internal map and compass with which to navigate.
Researchers have identified several compasses used by birds, Guglielmo says.
“The most important right around sunset is called the sun compass.”
Sunlight is strongly polarized near sunset, and birds can use this to find north and south, Gugliemo says. Other studies have found that birds also use magnetic fields and stars to get their bearings.
The map is largely a mystery, Cannings says. Magnetic fields, smells and even infrasound have all been suggested as its source.
While the actual route birds take during migration varies slightly year to year, many will hit up specific rest stops such as Big Lake to rest, refuel, or even stop and breed.
It’s vital for us to protect these regions if we want to preserve migratory species, Cannings says.
“Even a small patch of woodlot might be enough for them to refuel.”
Risk and reward
Migration carries a host of hazards, including buildings, predators and bad weather.
Those birds that make it are sometimes so exhausted that they die on arrival, Stoker says.
“It’s a very sad state of affairs,” he says. “They pay the price, some of them, in getting there, but once they get there, they’ll be able to raise a good family and start the cycle all over again.”
Migration is one of the most remarkable things in the world, Cannings says.
“You have all these animals that can fly and a lot of them take that to the extreme and move around the world.”