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.