The dramatic pageant of fall bird migration is beginning to occur in many parts of Alaska. Alaska is a crossroads for bird migration and enjoys a cosmopolitan avifauna during the summer months of breeding and nesting. Northern wheatears from Africa, long-tailed jaegers from the South Pacific, Arctic warblers from Asia and many birds from South and Central America come to nest and raise their young here. They take advantage of the 24 hours of daylight for feeding, the available high protein diet of an abundant insect population and a relative lack of competition for food and nesting sites. On this first day of August in the Denali area a blackpoll warbler, a bird about 5 inches in length from beak to tail, was showing the yellows and olive greens of its fall plumage revealing little trace of the black cap that distinguishes males in breeding condition and gives the species its name. Weighing less than an ounce, this bird requires enough fuel to fly as much as 6,000 miles, zigzagging its way back to South America.
In the distant past, blackpolls probably nested only in the evergreen forests of eastern North America. Slowly they extended their breeding range far into northwestern Canada and Alaska. Now the members of this northwestern segment of the population, instead of flying directly south, retrace every fall on migration the path over which the species originally expanded its range. It is no coincidence that this long-range flier has evolved longer, more powerful wings than most other warblers. The adaptability of these diminutive birds, whose home is alternately the boreal forests of Canada and Alaska and the tropical woodlands of Brazil, is impressive. They fly for three or four days at a time through the wind driven miles over the Atlantic and Caribbean.
The loud voice of a northern water thrush is frequently heard in a thicket on the edge of a bog nearby. This bird is not actually a thrush but a wood warbler and was named in 1808 before there was even a semblance of sensible bird taxonomy. This bird especially favors mangrove swamps in Central and South America during the winter months. Also in the area are Swainsons and gray-cheeked thrush, two beautiful songbirds which over-winter in mature tropical forests. Each species represents an incredible testimony to adaptation, cultivated through centuries.
Many adult birds leave the breeding territory before their young, even while food supplies abound. The early departure is a possible advantage to the older birds that arrive on the feeding grounds first and have first choice of food. Some of the birds of the Interior (of Alaska), such as ptarmigan and gray jays, seldom stray more than a few miles from their breeding territories. Others take part in long flights only occasionally; these irregular movements are called irruptions rather than true migration. Irruptions are characteristic of grosbeaks, crossbills, redpolls and many owls, all residents of the Far North that may fly southward when their winter food runs short.
The mystery of migration remains an apt cliché. We still do not know a great deal about the reasons and mechanics of bird migration. Our ancestors thought the abrupt disappearance of many familiar species such as swallows was because they hibernated like frogs in the mud beneath ponds. More imaginative souls ventured the theory that birds flew away each fall to the moon. Whatever the trigger, birds alter their behavior at the end of the breeding season when their young have flown. The barriers that each mated pair had put up against other individuals of their own kind during breeding begin to crumble. They become gregarious once again and many join in mixed flocks, forming a loosely organized group.
Like music, the rhythm of the seasons, the cycles of migration, of courtship and nesting, of silence and song are rhythms within rhythms. The world that birds represent stretches back from the present to millions of years ago, before factories and cities, highways and office buildings. Engaged in annual migrations between hemispheres, the enduring natural order is most vividly represented by birds.