About a week ago, the wind was howling at up to 60 miles an hour, blowing snow and causing hundreds of car accidents. The juncos who usually hold forth under the bird feeder scurried to the porch where they sheltered out of the wind. An opossum found a protected corner of the porch and curled into a tight ball to wait out the storm. The humans on Owl Acres lit a roaring fire in the fireplace and snuggled down to wait it out.
And now, only a few days later, redwing blackbirds are singing in the field, and yesterday our first robin appeared in the yard. He joins the cardinals, blue jays, finches, woodpeckers, chickadees, nuthatches juncos and sparrows who stayed all winter.
The spring migration has begun. It makes me wonder about the enormous effort these little birds expend to fly thousands of miles south, and then thousands of miles north again every year.
The accepted reason for this migration is simply that birds fly south because it’s warmer and there’s more food there during the northern winter. And they fly back north to their breeding grounds to find more and better nesting sites and food available in the spring and summer up north. It’s likely to be more complicated than that and fertile grounds for research.
What we see and hear on Owl Acres bears this out. What I never thought about though, is that while they’re raising their young in the summer months, they’re also preparing for the fall migration.
To be successful, a bird’s migration is dependent on preparation, the weather and the environment.
Before a bird embarks on thousands of miles of travel, it needs to store up relatively large amounts of fat. Our migrants do this by eating literally two or three times their weight each day before migrating. The abundant insects, seeds and other food found in their northern habitats help them layer on fat just under the skin and in their abdomens. They will burn it all on the journey.
Another important activity that many migrating birds complete while they’re still in their northern breeding grounds is to molt. Feathers don’t last forever, and generally need to be replaced once or twice a year. Molting requires a lot of energy to build those new feathers, so it’s best to get the job done while they have plenty to eat.
Weather is another important factor. Migrating birds wait for favorable wind conditions whenever possible before they head out on their migrations. Not only do storms and strong winds affect the birds’ actual travel, but migration timing has been honed over thousands of years, to coincide with the availability of food supplies. Robins arrive when the ground is warm enough for the earthworms to emerge from their winter huddles. The emergence of insects and buds guarantee the protein needed for egg production and to feed the chicks when they hatch. As weather patterns change, temperature-dependent activities like plants budding out and insects hatching may no longer coincide with day length and temperature fluctuations that signal migration.
Some 650 species of birds inhabit North America, and about 350 of these species are long-distance migrants. Others undertake shorter migrations. Migration patterns are not one size fits all. Each species has developed its particular way of doing. Some birds don’t migrate at all. They have sufficient food in their home habitat so they just stay put. On Owl Acres we see a dozen or so species of birds that live here year-round. Four species of woodpeckers—red-headed, red-bellied, hairy and downy–find plenty to eat in old wood and, these days, the suet blocks on our bird feeder. Their cousin the northern flicker, another woodpecker, gets its food by finding ants in the soil. Unlike its stay-at-home cousins, the northern flicker usually goes south when the snow cover is hiding the ants. We had very little snow this winter, and we saw at least one northern flicker who had decided to stick around.
Canada geese have also decided that they don’t all have to go very far to winter. Some just stayed in the neighborhood.
Juncos come from the forests in Canada to spend the winter under the bird feeder on Owl Acres. These hardy Canadians don’t need the tropics, but they’re happy to clean up all the seed that the bigger birds kick out of the bird feeder. Soon they’ll be off to Canadian forests.
Our long-distance migrants like Mr. Robin are coming back now. in the next several weeks, we’ll hear a lot of transients stopping over to rest before heading farther north.
Some birds travel in migrating flocks, and others fly solo. Some species fly by day, and others by night. They all seem to know where they’re going though. They use a complex set of tools to navigate. Like sailors, birds navigate by the sun and the stars. They can also sense the earth’s magnetic field. They use the position of the setting sun as a clue, and also recognize landmarks on the ground. There is some evidence that they may also use their sense of smell.
Birds that travel by night are often confused by the lights on communication towers and the lighted windows of tall buildings. This is especially problematic on foggy nights, and an estimated seven million night-flying song birds die each year due to collisions with manmade obstacles. Birds that migrate during the day are not safe from these collisions either. Thousands of years of evolution did not prepare them for glass windows or obstacles at these altitudes.
Although they are making the same trip each year with the same destinations, birds don’t necessarily follow the same path going north that they followed going south. They seem to know where the food supplies are and where good stopover places can be found in each season. They also seem to know where they were born and return to that place each summer.
With all this planning and calculating and navigating, it makes me think that calling somebody a birdbrain should be a compliment.
Photo by Author. Alt text: View out the front door at Owl Acres. The morning sun lights up a House Finch on the porch railing and a Canada Goose standing out in the yard. The Finch does not migrate. The Canada Goose migrates only as far as needed to find food and habitat.