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.
Time is short for the millions of migratory songbirds that journey thousands of miles north to breed on Alaska's North Slope. On this vast swath of Arctic tundra, which drops gently downward from the Brooks Range for about 130 miles until it meets the Arctic Ocean, the sun shines around the clock for just a few months, quickening the pace of life. Their arrival and departure cued by that nearest of stars, the birds race for the nesting territory and food they'll need to raise their young and prepare for the return trip south come autumn.
Many of the birds, such as white-crowned sparrows, American robins, savannah sparrows, and Lapland longspurs, are the same ones that regularly visit the Lower 48. When they arrive in the Arctic in late spring, they rely on the dried remains of last year's bog blueberry and bog cranberry, exposed as the snow melts. Then much heartier meals become available, like spiders, crane flies, midges, and caterpillars. "Just like we don't want to be feeding our kids sugar all the time--we want to be feeding them some protein as well, some tofu or chicken or beef--they want to be feeding their chicks arthropods," says Natalie Boelman, an Arctic ecologist at Columbia University's Lamont-Doherty Earth Observatory.
I've come here to the Toolik Field Station, tucked into the foothills of the Brooks Range, to tag along with Boelman and her colleagues, who are studying whether climate change is causing shifts between when Alaska's migratory songbirds arrive and breed and when the insects that the birds and their chicks rely on are abundant. The Arctic is warming faster than anywhere else on the planet, amplified by shrinking sea ice and glaciers and shorter snow-covered seasons that leave behind darker, less reflective water and land that absorb more heat. Over the past century temperatures across the globe have increased by an average of 0.74 degrees Celsius, while the Arctic has warmed at nearly twice that rate. At the same time, higher temperatures are spurring the northward march of shrubby vegetation onto the open tundra; the dark, leafy plants soak up more heat and trap more snow. This insulates the ground, raising soil temperatures and releasing extra nitrogen that gives the shrubs even more of a leg-up.
How songbirds will adapt to the increasing variability is a mystery. Melting snow caused by warmer springs could lead to an explosion of flowering plants and bugs before chicks have hatched to take advantage of it. Even a one-week mismatch could spell trouble for these migrants. Boelman, borrowing from biologist Eric Post at Penn State University, compares it to lunchtime in the cafeteria: "Imagine you go to lunch at noon every day at your cafeteria at work, and then all of a sudden that cafeteria stops serving lunch at noon and opens at 11, but you don't know and you keep showing up at noon," says Boelman. "You're going to miss lunch or just get the tail end of it, the scraps."
Although the life histories of migratory waterfowl and other animals and plants have been more thoroughly studied in the Arctic, "the migratory songbird picture is just a big hole in our knowledge," says Laura Gough, a plant ecologist at the University of Texas in Arlington and Boelman's co-investigator. "We just don't understand what's happening." Evidence of change is abundant in more closely monitored species. A northward expansion of winter moths has led to outbreaks in Scandinavia's Fennoscandia region. Red foxes are displacing Arctic foxes in Norway and parts of Alaska. Forage plants, a staple of the caribou diet, are unfurling their leaves earlier in Greenland, before the caribou deliver their calves. With fewer food options, the nutritional quality of the females' milk is declining, reducing the survival rates of their offspring.
The fate that befalls songbirds at the top of the world could have ripple effects in the Lower 48. "Because the birds are migratory, if they arrive on the tundra and bugs are peaking at different times, or there are too many storms and they can't breed, and it happens several years in a row, it's going to affect their population numbers farther south," says Gough. This matters because migratory songbirds provide valuable "ecosystem services," keeping insect populations in check and dispersing seeds across great distances. On top of that, some of these birds are regular visitors to people's backyards, trusty fixtures in our daily routines. "They're just such a big part of the acoustic landscape," says Boelman, "people would really notice when they open their windows and they're not there."
We set out single file, donning Gore-tex parkas, mosquito head nets, rubber boots, bug and bear sprays, and binoculars, all of which make the otherwise pleasant, mid-70s temperatures feel downright toasty. Graduate students and undergrads lugging nets and other field gear fan out in different directions. It's quiet, aside from the high-pitched whine of the constant swarm of mosquitoes determined to invade my head net.
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.
Marcel Visser, an evolutionary ecologist from the Netherlands Institute of Ecology, has studied various avian species, including the pied flycatcher, a migrant that overwinters in Africa and breeds in Northern Europe every spring, and the great tit, a widespread resident of Europe, Asia, and the Middle East. In a 2006 study in Nature, Visser and colleagues reported a 90 percent decline among nine Dutch populations of the pied flycatcher in areas where food availability peaked too early due to warmer spring temperatures. By contrast, in areas where no mismatch occurred, the team found little to no population decline. In more recent studies, Visser and his colleagues have documented shifts in seasonal timing in various bird species, including great and blue tits. While some appear to be keeping up with the changes, others are not.
Migratory songbirds are particularly vulnerable, says Visser, because day length, rather than temperature, is their cue for when to leave their winter residences. "The problem for long-distance migrants is they have to make a decision about their timing in a very different place than where it really matters, which is in the breeding area," he says. The fact that the Arctic is warming so fast is a "ticking time bomb" for migratory birds, "because these birds are not taking temperature into account."
Cagan Sekercioglu, a bird conservation ecologist at the University of Utah, has studied birds the world over and recently compiled a comprehensive database of the ecology and ecological functions of most of the world's 10,000 bird species. In a 2008 paper in Conservation Biology, Sekercioglu and his colleagues modeled and analyzed potential extinction rates of more than 8,400 land birds, representing 87 percent of all bird species, under 60 different scenarios, including variables such as warming projections, habitat loss, and shifts in elevation ranges. In the team's worst-case scenario, some 2,500 bird species--or almost a third of the world's land-bird species--could be committed to extinction by the year 2100 if no conservation actions are taken.
"Since 2008 a lot of things have headed in the wrong direction," says Sekercioglu, including rising greenhouse gas emissions and waning political will toward an international agreement to limit those greenhouse gases. Yet there are positive signs, he adds, such as a recent Nature study showing that the most extreme projections are looking less likely. And in June President Obama committed to leading international efforts to address global climate change when he rolled out his ambitious global warming action plan.
"Climate change threatens all our victories in bird conservation and introduces new challenges related to shifting ranges and the ecosystems that birds and people depend on," says Gary Langham, vice president and chief scientist of the National Audubon Society. Because Alaska is the headwaters of the migratory bird flyways, the state is at the forefront of Audubon's concerns about climate impacts, says Langham. "A thorough understanding of how birds will respond to the uncertain climate future allows Audubon to make wise conservation investments to save the future of our birds."
On another warm day at a field site about 20 miles farther south, the researchers are checking on several nests they found the week before and hunting for new ones. Some of the students head off with sweep nets to collect bugs and to check pitfall traps, while others use metal poles to probe the brush for sparrows or longspurs. Boelman and Wingfield inspect their equipment, including an acoustic device with microphones and a recording unit that captures birdsong in order to document the presence of particular species at various times throughout the summer.
At this site, webs of snow still cling to the mountains in narrow rivulets. Green moss blankets the hillsides until the hills become barren peaks, jutting into the clouds. We spot swallows, a sandpiper, and a long-tailed jaeger with boomerang-like wings and a showy plume of ribbon extend- ing from its tail. Fireweed--dainty wildflowers with fuchsia blossoms--and the tiny pink bells of bog rosemary dot the landscape. One of the only visible reminders of humans is hard to miss: the trans-Alaskan pipeline, which zigzags like a giant metal snake across the hilly plains, carrying crude oil southward to Valdez.
After scouring an area for a half-hour and crawling on all fours, the researchers find an impossibly camouflaged white-crowned sparrow nest in a thicket of shrubs. Closer inspection reveals five lightly speckled eggs, about a half-inch long, nestled inside. By the end of June the team has found 20 sparrow nests and 27 longspur nests.
What the researchers are learning at the top of the world will provide key information to plug into global ecosystem models, which will then generate better forecasts. And it will give conservationists and wildlife managers a clearer idea of what's to come--perhaps allowing time to preserve species in the Lower 48, where shifts aren't occurring as rapidly. Ultimately, though, climate change is a radical experiment with nature. In a sense, all the researchers can do is continue to wait. If the birds start missing lunch, they'll be right there, watching and, perhaps, even hoping.
This story originally ran in the September-October 2013 issue as "Out of Sync."