|
 Some classically migratory birds, like the Swainson’s hawk, do all seem to get the urge to pack up and fly a few thousand miles from the plains of the Midwest to the plains of Argentina at almost the same time each fall. The cue seems to be the photoperiod, or the amount of time the sun is up each day. This tells their internal timer that soon the prey they live on will be disappearing for the winter and if they want to survive, they must go south to find food. In fact, food is the real reason birds migrate, whether it’s a seasonal “drift” or a full-blown transcontinental voyage. This is why birds that live permanently in milder climates don’t often migrate, since the things they eat don’t vanish with the passage of the seasons as they do in the middle latitudes. It’s also important to remember that we can never say “never” or “always” when speaking about nature, including the migration of birds. There are sometimes a few who like what they find in one area and decide to set up a permanent home.
 One species that winters in Arizona is the sandhill crane. In the summer, huge flocks of sandhills live on the grasslands of Siberia where they breed. Grains and insects are plentiful there and the human population is relatively sparse. In the fall, they migrate over the Bering Sea, across Alaska and Canada, through the great plains of the Midwest, and end up wintering in Arizona. Foraging on corn stubble in the Sulphur Springs Valley near Elfrida, a huge colony of sandhills remains here until late February. Then they begin the long flight back north, meeting other large flocks from New Mexico and Nebraska, to continue back to Russia. One tagged sandhill has been satellite-tracked making two such treks from Whitewater Draw north of Bisbee to summer breeding grounds in Siberia on successive years.
  
Eagles, especially bald eagles, don’t migrate in a group like cranes and some other birds do. This might be because they don’t need the protection of a flock as they travel, and they don’t all go to the same place at one time. They are primarily piscivorous (fish-eating) and as the weather gets colder, the rivers and lakes they work for food begin to freeze, making fishing difficult if not impossible.
Recently I went to Haines, Alaska, to photograph bald eagles. It was the last week in November and the temperature hovered around -25 degrees. There aren’t many birds other than penguins that will tolerate this sort of climate, but around 3,000 bald eagles will move to the Chilkat River above Haines and hang out there for months. Why? What attracts birds to an area so cold when most others are heading to warmer territories? Simple answer: FOOD!
 
In this unique spot along the river, warm springs feed the Chilkat and for a space of about three miles, the river never totally freezes over. A certain species of salmon know this and come to the open water to spawn, and then die. The bald eagles also know this, and they come for a veritable smorgasbord. No energy need be expended on hunting, or even flying very far, as thousands of salmon die and are eaten by the eagles, ravens, and magpies who are willing to tolerate the arctic conditions in exchange for free food! I was told that the wintering eagles don’t even kill the salmon they eat, preferring to wait until they die naturally after spawning, saving even that much energy.
But obviously all eagles don’t go to the Chilkat Valley. Lots of other eagles throughout Canada and the higher latitudes of the United States set their sights on warmer habitats. In Arizona, we have approximately 100 resident bald eagles that live and breed here. As demonstrated by Sutton, our own fledgling of three years ago, southwestern balds do migrate north in the summer and spend the warm months in places like Alaska and Minnesota. Then when the days grow short, they head back to Arizona for the winter and to breed near their natal nest areas. During the winter, around 600 “snowbird” eagles will arrive, having migrated from other areas, making use of our open, unfrozen water, scarce as it may be. They will hang out here until the water up north thaws and their preferred food again becomes available. Recently two such migrants were seen around a lake in Scottsdale. (So if you keep your eyes open, your golf-playing in-laws aren’t the only visitors from Chicago you might see this winter!)
|
|
