The fall migration is winding down. Or is it? Most songbirds and many raptors have departed, but the waterfowl are just getting started. Schoodic Institute in Winter Harbor conducts an annual SeaWatch, counting the scoters and other seabirds that stream southward past Schoodic Point in autumn. At the beginning of October, the scoters hadn’t even started yet. This might be a good time to ponder the whole concept of migration. It’s not just “birds go south for the winter.”
Migration is the wholesale movement of a species from one environment to a different one. Often, there is a seasonal component. That’s true for birds. It’s even true for lobsters. Many lobsters move to deeper water offshore in winter.
Some migrating birds aren’t in any particular rush to get where they’re going. Arctic terns are the world’s champion migrants, traveling more than 18,000 miles a year. Over a lifetime, they may travel 1.5 million miles. That’s three trips to the moon and back.
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The hundreds of Arctic terns that nest on Maine islands left for Antarctica several weeks ago, but not on a direct flight. They typically head over to Europe and down the coast of Africa, maybe with a side trip into the Indian Ocean, before returning to the Western Hemisphere. They meander to wherever there’s plentiful food, sometimes spending a month in mid-ocean before continuing their journey. Because they spend opposite seasons near each pole, they experience two summers. No animal on earth enjoys more daylight.
Meanwhile, the record for the shortest annual migration is held by the blue grouse. It spends its summer in the high-altitude, pine-dominated forests of mountains out west, then heads downhill to spend the winter in deciduous habitat. Their migration may be as short as 300 yards. More than 100 bird species in North America have demonstrated some tendency to migrate seasonally up and downslope.
A lot of our Maine birds migrate according to food abundance. Some years, red-breasted nuthatches flee the state. Other years, they don’t. Black-capped chickadees will move southward if they anticipate a bad winter.
Currently, the blue jays are really annoying me. Last year, they emptied my bird feeders faster than I could fill them. They stole big loads of seeds and hid them away, caching plenty of food for the winter. Then they left anyway. I’d estimate 10-20 pounds of last year’s seeds are still stashed in the trees somewhere around my house. I can forgive them for one year, but now they’re doing it again!
Virtually all finches migrate in haphazard fashion. They simply meander until they find food. Some years, a lot of Canadian finches wander down here. Other years, they don’t. Pine grosbeaks and common redpolls are two Canadian finches that don’t breed in Maine, but do visit in some years. Biologists who monitor food supplies in Canada note a good fruit crop in the provinces, and predict that the pine grosbeaks won’t come down into the states much this year. Likewise, the seed crops in birches and aspens that nourish Canadian redpolls are healthy this year, so not much southward movement is expected.
Pine siskins are small finches that breed in northern Maine and across Canada. Last year, the food crop for them was so poor, they totally vacated the state, journeying much farther south than usual. Purple finches also disappeared for much of the winter. Both are expected to stick around Maine in bigger numbers this year.
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Bohemian waxwings are expected to find plenty of winter ash berries across Canada, so we may not see as many down here this year. They’re odd-ball wanderers, anyway. Most breed west of Hudson Bay, and all the way up the Bering Sea in northern Alaska. When they show up in Maine, their migratory route is more west-to-east than north-to-south.
And then there is that whole climate change thingy. The length of daylight has long been understood as one trigger for telling birds when it was time to go. As the earth warms, we may watch that date gradually become later. I’ve been a little surprised to watch ospreys and great blue herons lingering around my house later than usual this year. But why the surprise? Not only was there no frost on any night in September, I don’t recall a daytime temperature below 55.
By now, most of our broad-winged hawks are crossing Mexico, headed for the Amazon Basin. Our bobolinks are reaching the pampas in Argentina. But some of our less ambitious birds are just goofing off.