Arctic Researchers Race to Uncover Effects of Global Warming on Songbirds
Ornithologists are in a race against time to document shifts at the top of the world that could foreshadow what's to come in lower latitudes.
Uphill from the gently flowing Kuparuk River, we take our positions and begin our stakeout for white-crowned sparrows and Lapland longspurs, hoping to track down their nests. The search is not for the impatient. The strategy is to watch and wait and listen. Sometimes for hours on end, until someone spots a bird. Then the researchers track its movements, and look for signs, such as carrying food, to determine whether it has chicks on a nest. "This is very much a game of clues, deductions, predictions," says John Wingfield, his binoculars perpetually trained on the shrubs in front of us. He remains oblivious to the thick mat of mosquitoes and horseflies blanketing the shoulders and back of his dark-blue fleece. An environmental endocrinologist from the University of California-Davis and a project co-leader, Wingfield has returned to Toolik almost every summer since 1987 to study birds.
The week before, the team tracked down 16 longspur nests. Sparrow nests are proving much more elusive. The Lapland longspur is an Arctic specialist that builds its nests between the knobby tussocks on the open tundra. It winters in the Midwest and central United States and has evolved to cope with the severe, unpredictable conditions of springtime in the Arctic. Despite this week's high temperatures, "by Friday there could be two feet of snow and below-freezing temperatures," says Wingfield. Harsh conditions early in the season sometimes force the birds to retreat back over the Brooks Range, where there is more competition for fewer resources. The white-crowned sparrow mates as far south as New Mexico, and the tundra represents the northernmost reaches of its breeding range. The bird hides its nests in dense thickets of treelike shrubs such as willows and dwarf birch, making the five-inch- wide structure excruciatingly difficult to find.
When the researchers have the good fortune to find a nest, they observe what types of material they're constructed from and count the eggs. (Longspurs build their nests with grasses and ptarmigan feathers, while white-crowned sparrows prefer to line theirs with caribou or moose hair.) They then mark the nests with flags and identification numbers written on Popsicle sticks, and record the exact locations so that they can easily revisit them. When the chicks hatch, they record their weight. When they grow to juveniles, researchers record muscle size and color and body fat before banding them.
During the past four years the team has found a tight coupling between the birds' arrival and nesting on the tundra and the pulse of food resources. Discovering the link has required going beyond surveying nests and hatchlings. Gough's team painstakingly collects and counts bugs to understand what the birds are eating and how that changes throughout the season. They sweep nets across 100 meters of tundra at a time and catch bugs in "pit-fall traps"--party cups with ethanol inside placed in holes in the ground to trap and preserve their unlucky catches, which they pick up two days later. To monitor how vegetation patches shift, Shannan Sweet, a Ph.D. student of Boelman's, marks out meter- by-meter "quadrats" with flags and labels. She records everything from when plants bud and flower to when berries ripen. Sweet also photographs the quadrats every few days until snowmelt, and then weekly after that, to track the shifting snowmelt and patchiness of the tundra from year to year. One important question the researchers aim to answer is how the encroaching shrubs might affect which bugs, and how many of them, are available for the birds and when.
Throughout the day we hear the squeaky-gate song of the savannah sparrow, the trill of a yellow warbler, the quick tink, tink, tink of a hoary redpoll followed by its machine-gun-like juh, juh, juh. A glaucous gull glides overhead, and two greater white-fronted geese make a noisy exit of porpoiselike belches after wading in the river.
Following a particularly long lull in activity, an almost electronic chirp emanates from the brush below us, an alarm call from a white-crowned sparrow, possibly because it has spotted us. Wingfield is staking out a shrubby labyrinth beneath us when he makes an urgent call over the radio: "Down here by the river. He's got a beak full of food. He flew up to the bush closer to you. There he is, flying. Got it?" An adult zips by, its beak stuffed with insects. "Got it," Boelman responds, glued to her binoculars. From across the valley, two graduate students radio in that they've located their holy grail, a white-crowned sparrow nest, with five hatchlings inside, about four days old. "Yahoo!" Boelman exclaims. She radios back that we're going to sit tight, waiting for our sparrows to reveal their nesting sites. Boelman and Wingfield wait nearly four hours--to no avail. They'll have to try again another day.
While Boelman, Wingfield, and Gough track what's happening in Alaska's Arctic, other researchers have been studying the ecological effects of climate change on birds across the globe.