Ker Than, National Geographic News 8 Aug 08;
Habitat destruction and climate change are making migrations increasingly difficult for many species, but it's not too late to bring these visually spectacular and environmentally critical mass movements back, according to a new study.
Migrations are one of the animal kingdom's most widespread phenomena.
They are seasonal tests of endurance, collective journeys often taken at great costs by birds, whales, land mammals, insects, and other creatures that are wired to roam.
Scientists estimate that one-third to half of all animals—and even some microorganisms—migrate during part of their lives.
"Even slime molds migrate," said study co-author Martin Wikelski, a zoologist at the Max Planck Institute in Germany and a National Geographic Emerging Explorer. Wikelski's study appeared last week in the journal PLoS Biology.
According to scientists, human actions are threatening many migrations. Habitat destruction, the creation of obstacles such as dams and fences, overexploitation of natural resources, and climate change are combining to make migrations increasingly difficult for many species.
Global warming, for example, is changing flowering times and other natural cycles, driving many birds and insects to move their ranges or arrive before or after their food sources have emerged.
Many of the planets great migrations have already vanished. The sight of vast bison herds roaming North America's Great Plains or multitudes of passenger pigeons darkening the skies as they migrated from Canada to the southeastern U.S. are things of the past.
Not Too Late
By increasing public awareness of the plight of migratory animals and committing to the preservation not only of individual species but also their way of life, many migrations can still be saved, write Wikelski and study co-author David Wilcove of Princeton University.
The authors argue that migrations should be saved, if not for the sheer awe that seeing millions of animals moving with one purpose elicits, then for their ecological importance.
Migrating songbirds, for example, snack on plant-eating insects that might otherwise destroy crops or forests during their layovers.
Salmon transport nutrients from oceans to rivers in the form of wastes, eggs, and sperm as they swim upstream to mate.
"What we really want to protect is the natural phenomenon of abundance," Wilcove said. "If we wait until migrating animals are endangered, then we lose both the ecosystem benefits associated with their abundance and also the wonder and majesty of migration."
Unique Challenges
Every migration scientist has his or her own favorite animal migration. Wikelski remembers standing on a New Jersey beach a few years go, transfixed by a moving wall of dragonflies migrating south from Canada and the northern U.S.
"All you see in the view of your binocular is just one dragonfly after another, zooming through your field of vision," he said.
But protecting the migratory routes of dragonflies and other transient creatures is fraught with unique social and political challenges, the authors write.
Their journeys can cross many state and country borders, so their preservation will require international cooperation.
But Wikelski sees hope in joint projects, such as one between Israelis and Palestinians to understand and protect birds migrating between their home states.
"Vultures go between Palestine and Israel, and Syria, and Lebanon. Storks and cranes do the same thing," Wikelski told National Geographic News. "Eventually, people will understand that its just one planet."
Alistair Drake is a migration scientist at the University of New South Wales in Australia who was not involved in the research.
The new paper "implies a need for a more extensive reserve system, and more constraints on blocking developments, than someone focused mainly on resident species and breeding habitats might have envisaged," Drake said.
As the world faces food and fuel shortages, we could face some uncomfortable choices, Drake added. "It's easy to envision a situation where you have a choice between conserving an important stopover habitat or growing food or biofuel on it."
But Wikelski believes humanity is up to the task.
"It's like global warming," he said. "You have to alert people, and after a while, the public knows about it and they do something about it. Thats when the big changes will come about. I think theres absolute hope."
