By Sharon Oosthoek, CBC News
Bird migration looks like a bad idea at first glance — all that energy needed to fly thousands of kilometres, all those predators along the way and the promise of doing it all over again just a few months later.
But of course Mother Nature knows exactly what she is doing. If you've ever wondered, as we did, what all that back and forth across the sky is about, read on.
Why migrate in the first place?
Two words: food and babies. It turns out the longer days of the northern hemisphere's summer mean a bumper crop of yummy bugs, which in turn means more baby birds.
"Even though migration is quite an investment and quite risky, the payoff can be pretty huge," says biologist Jody Allair of Bird Studies Canada, a non-profit conservation group.
"If you've spent any time up in a bog in Algonquin Park in early June, you'll know why. The food abundance is just out of control."
But the good times don't last forever. Starting in late summer, the bug banquet tapers off, and within weeks there's a chill in the air signaling the killing cold to come. Time to head south.
How do birds' know when to move on?
The trigger is changes in daylight — less of it in the fall and more of it in the spring. While it's not fully understood, scientists believe birds' hormone levels are affected by shifts in daylight hours, signaling that it's time to get going.