By Greg Hoch
— It’s September and the fall migration is on.
Migration seems pretty simple, move north in the spring and south in the fall. Once you start looking at it in detail, it’s incredibly complex.
Birds migrate at night. The air is less turbulent and cooler during the night. Put on a down-filled winter coat and flap your arms for seven or eight hours and see how hot you get. Flying by night also allows them to navigate by the stars. Celestial navigation also causes them to get confused by lighted windows and the blinking lights on communication towers, often costing them their lives.
In the spring, birds closely track the calendar, actually the day length. Often we can predict when a species will arrive within a day or so. This is because there is a rush to get to the breeding grounds and establish a territory. Fall migration is much less predictable. Birds hang out, gorging themselves on fruits and seeds, and then catch a cold front when it comes.
Birds can gorge themselves all day and then fly all night. In some cases they can almost double their weight with fat accumulation during the day and then burn that all off that night. Imagine doubling and halving your weight every twelve hours!
Some birds will safely follow the coastline while others will dangerously head off over open water such as the Gulf of Mexico. If a weather front moving in from the north catches them in mid-flight, there’s no place to stop and rest. Millions of birds will run out of energy flying against the headwind, fall into the ocean, and wash up on the beach. There are records of millions of birds washing up on Gulf Coast beaches in a single morning.
The bar-tailed godwit, leaves Alaska and flies straight through to New Zealand. This takes about nine days and is a distance of a little under 7200 miles, without any stops. The blackpoll warbler nests in Alaska, flies east to New Jersey, and then sets out across the Atlantic for a two-day nonstop flight to South America.
Some sandhill cranes migrate from the southern states up to Minnesota where they breed. Others fly past Minnesota and go all the way to Alaska. Some pass Alaska and nest in Russia.
Some species don’t migrate at all. Pheasants, prairie chickens, and sharp-tailed grouse stay year round. The tiny chickadee also overwinters here while a big fat mallard with an inch or more of insulating feathers heads south.
Snow buntings and redpolls migrate from Canada to Minnesota. For them, Minnesota is the south. The question each species has to face is whether it’s more difficult to survive a Minnesota winter, or to survive flying from Minnesota to South America and back. Both options are risky, which is why 80-90 percent of birds never see their first birthday.
The next time you see those migrants at the birdfeeder, imagine what those little bodies have gone through and all the places they’ve seen.
Greg Hoch is a prairie habitat evaluation ecologist with the Minnesota Department of Natural Resources stationed at the Farmland Wildlife Research Unit in Madelia.