The melody of bird song on a summer morning in the boreal forest is one of the greatest natural sound experiences on earth. Listen
About 200 species of birds migrate to the North American boreal forest every summer to raise their young. They come from the United States, Canada, Mexico, Central and South America, and even as far away as Australia. Africa, and the Antarctic.
What makes the far north so attractive that a bird would literally risk its life, flying vast distances to come here?
There are several reasons why birds such as Swainson's thrushes, peregrine falcons and golden plovers would travel 7,000 miles from southern South America to nest and raise their young here. One reason lies in the availability of wild land and relative safety where the males can set up breeding territories and females can find nesting spots. Much of the boreal forest is far from urban areas, industrial developments, and other human activity.
But perhaps the most important reason to journey so far is the long northern days, which bring lush plant growth and an incredible abundance of insects like mosquitoes, which are essential for birds to feed their growing nestlings.
Insects are rich little packets of protein. Even birds that are vegetarians for the rest of the year—eating only seeds or other plant materials—need insects to give their offspring a healthy start and rapid growth. Although the boreal summer is only a few months long, it also brings endless daylight so the birds can work continuously to establish their territories, build nests, lay eggs, and keep their hungry hatchlings well fed. Everything seems to happen at high speed during the northern summer, so the newborn birds quickly grow big and strong enough to make a long migration south when the northern days begin to shorten.
Millions of mosquitoes can create pure misery for humans and other mammals, but birds actually thrive on them. And the earlier a bird is here, the better, ensuring the best territories, and nesting spots, and the longest possible summer season for their offspring to grow. Among many species, hatching time coincides almost perfectly with the emergence of insect hoards. Of course, this is not pure happenstance, but another example of the way animals evolve in concert with the demands and promises of their environment.
Birds who stay in the boreal forest all winter must face extreme cold, darkness, and storms…but in exchange, they are on the mating and nesting grounds well ahead of the migratory species. So ravens, ptarmigan, gray jays, chickadees, redpolls and gyrfalcons are already well into their breeding cycle when migrating birds such as thrushes, warblers, and sparrows are just arriving.
The advantages of staying put are balanced against the challenges of making it through the long and bitterly cold boreal winter. For this, they have evolved special strategies for survival.
Ptarmigan, for example, dive into the deep, soft snow, making an insulated cave where the temperature stays just below freezing even while temperatures above the snow drop to minus fifty or colder. For walking on top of the powdery snow, they have feathered feet, which act like miniature snowshoes, keeping them from sinking.
Gray jays cache food all summer in places they can find in the winter, like under the bark of trees. Amazingly, months later, these jays can remember hundreds or thousands of places where they have hidden their food last summer!
The total number of birds that come to the boreal forest in summer is mind boggling—an estimated billion sparrows and two billion warblers. Along with them come throngs of swallows and woodpeckers, robins and thrushes. Birds whose beauty and songs brighten the world farther south depend on the boreal forest to ensure there will be future generations of these feathered gifts.
In addition to songbirds, forty percent of North America's waterfowl breed here including ducks, geese, swans, grebes, and loons. One-third of North America's shorebirds, such as sandpipers, plovers, and phalaropes also spend their summers here.
And at the end of the season, about 5 billion birds—adults and their offspring—leave the boreal forest, heading south to every continent on earth. This includes the arctic tern, a graceful water bird that nests in among far northern lakes and rivers, then flies to the waters off Antarctica—a round trip journey of more than twenty thousand miles every year. As a reward for these flights between summer in the far north and the far south, arctic terns spend more time in daylight than any other creature on earth.
Many changes are happening in the boreal forest where these birds raise their young. This includes loss of habitat due to oil and gas development, mining, and hydroelectric projects. Clearcut logging destroys about 2.5 million acres of boreal forest each year. This means an area almost as big as the state of Connecticut is lost annually to birds that nest in the forest. And it undoubtedly contributes to the decline in bird populations. Most of the wood from these clear cuts goes to make newspapers and catalogs…throwaway items.
The boreal forest is also showing the effects of a warming and drying climate. There are more wildfires now and some lakes and wetlands are drying up, which is not good news for the animals and birds whose lives depend on forests and waterways.
And those clever gray jays and other birds who stash their food have problems when cold temperatures come later in the fall—their food can rot, leaving them with less food to get through the winter. These food caches are also important for feeding the young gray jays that hatch in April, before many of the other food sources are available.
Along their migratory routes, boreal birds are also losing habitat—places where they rest and feed to fuel their journeys. And another problem—collisions with radio and cell towers are responsible for the deaths of millions of migrating birds each year.
Some boreal birds spend the winter in tropical forests that are being cleared for lumber and agriculture. This partly explains why at least 40 species that nest in the far north in summer are declining, including the Swainson's thrush.
Decisions we make in our daily lives—and as nations—will determine if these beautiful creatures will continue to jewel our world and to sing their haunting love songs.
It's hard to imagine a world without this sound.