For Many Species, Moving Day Has Added Stress
Jim Robbins New York Times 19 Dec 11;
HELENA, Mont. — Every fall the calliope hummingbird, which weighs about as much as a penny, braves high winds and bad weather to migrate from Canada and the northern United States to as far south as Mexico, then back again in the spring — a total of 4,000 to 5,000 miles.
The journey is one of several dozen “spectacular migrations” — in the air and on land — that are chronicled in a new report by the Wildlife Conservation Society. But the report warns that these migrations are in peril.
“Long-distance migrations as a whole are rapidly disappearing,” said an author of the report, Keith Aune, a senior conservation scientist here in Montana for the wildlife group, which is based at the Bronx Zoo in New York.
The report surveyed wildlife biologists across the Western United States, where most of the large-scale migrations still take place. It details 24 terrestrial and 17 aerial migrations; a later report will take up ocean migrations. There are many more imperiled migrations, Mr. Aune said, but these are both the most important and the most likely to survive if they receive public support.
Long-distance migrations are not only a spectacle, he said; they are crucial to keeping wildlife species extant in a changing world. “They are about survival,” he continued. “When we block migrations, we lose the ability to sustain a population.”
It has happened all too often, he said, citing the vast migrations of bison across the Great Plains in the 19th and early 20th centuries. While there are still bison, they are largely limited to a few reserves, like Yellowstone National Park.
Then there was the passenger pigeon, now extinct: In 1866, a migrating flock was so immense it took 14 hours to pass one spot in Ontario.
Such stories can win support for preserving the corridors that wildlife use to migrate, Mr. Aune said, adding: “If I say, ‘We need to protect ecological connectivity,’ people will say, ‘What is that?’ We have to have something the public can grasp. Spectacular migrations have great storytelling power.”
Wildlife migrate to seek water or food at different times of the year, or to breed. The ability to freely move across the landscape could become even more important as the climate changes and wildlife need to adapt — following the movement of the plants that they eat or looking for new sources of water as old sources dry up.
The problem is that corridors are often very long, and many obstacles crop up because migrations have not been recognized or protected. There are natural obstacles, too. This year, for example, many pronghorn antelope — the fastest land mammal in North America — drowned as they tried to cross the flooding Missouri River on their way to fawning grounds in Canada.
David Wilcove, an ecologist at Princeton and the author of “No Way Home: The Decline of the World’s Great Animal Migrations” (Island Press, 2007), thinks storytelling about great migrations could be sound strategy.
“I don’t think the notion of biodiversity per se has gained any traction with the public,” he said. “But people have been fascinated by animal migrations since the first hominids stared at herds of wildebeest. And the fascination persists to this day.”
Oswald Schmitz, an ecologist at Yale, agreed, though he added that evidence was still lacking to say that loss of these corridors could result in extinction.
“We need to instill a different kind of ethic, and this report does a great job of showing why we need to protect large landscapes,” he said. “It’s a narrative that reaches out to the nonscientist on why we need to protect large landscapes.”
Protecting large landscapes for migration, biologists say, is also a benefit because it assures the protection of a wide range of other species that occupy smaller areas.
The longest migration included in the report is the 400 rugged miles covered by some Alaska caribou. Among other threats, it may encounter problems as the changing climate brings more snow; that could slow the animals’ journey and make them more vulnerable to wolves. Perhaps more than any other species, the report says, the caribou embody a story of “survival through adaptive movements and migration.”
But in sheer mileage, their journey is dwarfed by that of the arctic tern, which travels up to 24,000 miles in a year, flying from one pole to the other, round trip. That migration may be threatened by human development at places where the terns stop during their journey.
Three species of bats have a particularly specialized type of corridor, the report says. The Mexican long-tongued bat, the Mexican long-nosed bat and the lesser long-nosed bat all spend time in the American Southwest, and all migrate at different times to Mexico, feeding on nectar, pollen and fruit in their migration corridor. The main threat is development of land in the “nectar corridor,” which has flowering plants that provide food for their trip.
As migration routes are disrupted, other species can be affected too — including humans. Take the case of migratory songbirds, whose numbers are down across North America.
In the spring, these birds eat 3,000 to 10,000 tons of insects each day as they travel. “It’s a legitimate concern,” said Dr. Wilcove, of Princeton. “Presumably with the decline of songbirds, insect damage to crops and forests could be worse.”
