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The
New York Times
January
1, 2008 Tuesday
by Carl
Zimmer
The world is etched with invisible
paths, the routes taken each year by uncountable swarms of
geese, elk and salmon, of dragonflies, zebras and leatherback
turtles.
Their migrations speak to us in some
unfathomably deep way. Birders flock to stopover sites like
Cape May, N.J., to watch birds on their journeys to the far
north in the spring and back to the tropics in the fall.
Eco-tourists head for the Serengeti to train binoculars on
herds of wildebeest that stretch to the horizon. American
schoolchildren watch monarch butterflies hatch from chrysalises
in their classrooms and then see them off on their trip to
Mexico.
But in his new book ''No Way Home,''
David Wilcove, a Princeton biologist, warns that ''the phenomenon
of migration is disappearing around the world.''
Despite their huge numbers, migratory species are particularly
vulnerable to hunting, the destruction of wild habitat and
climate change. Humans have already eradicated some of the
world's greatest migrations, and many others are now dwindling
away. While many conservation biologists have observed the
decline of individual migrations, Dr. Wilcove's book combines
them into an alarming synthesis. He argues that it is not
just individual species that we should be conserving -- we
also need to protect the migratory way of life.
As a scientist, Dr. Wilcove finds the
disappearance of the world's migrations particularly heartbreaking
because there is so much left for him and his colleagues
to learn. What are the cues that send animals on their journeys?
How
do they navigate vast distances to places they have never
been? How do some species travel for days without eating
a speck of food?
Scientists will never be able to answer
those questions for migrations that have been wiped out.
The journeys of tens of millions of buffalo on the Great
Plains will remain a mystery.
But today, scientists are inventing
new ways to learn about the surviving migrations. They can
tag dragonflies with tiny monitors and analyze the chemistry
of feathers to discover the hidden wintering grounds of birds.
Unfortunately, a lot of what they are learning is about all
the threats a human-dominated world poses to migrations.
Animals are particularly susceptible
to hunting as they migrate, because they swarm in vast groups
at predictable times and places. The survival of migratory
animals depends on all the habitats along their journey.
And a migratory bird's numbers may dwindle if the forests
where it winters are cut down, or if its summering grounds
are destroyed, or if its stopovers are eradicated.
At least the birds enjoy the luxury
of flying; when salmon in the Pacific Northwest swim from
the oceans into rivers to reach their spawning grounds, they
now must struggle past chains of dams. Redfish Lake in Idaho
was named for the color it turned when it filled with thousands
of sockeye salmon that had just swum the 900 miles from the
sea. This year only four sockeye reached the lake.
In ''No Way Home,'' Dr. Wilcove also
describes threats that have only recently come to light.
Cowbirds can devastate migrating songbirds in the United
States by parasitizing their nests, for example. Cowbird
mothers throw out the songbirds' eggs and lay their own instead.
It turns out that fragmenting forests are an excellent habitat
for cowbirds.
In years to come, Dr. Wilcove warns,
global warming may come to have a huge effect on migrations,
by dismantling ecosystems and leaving migrating animals without
the food they depend on.
It is difficult to come up with a strategy
to preserve a phenomenon as multifaceted as an annual migration.
If a species of tree that lives only in part of Florida is
endangered, the solution is straightforward: try to conserve
that little patch of habitat. But migratory animals don't
respect international borders. The preservation of their
migrations demands that countries to work together to find
solutions. Dr. Wilcove points to some good models -- Tanzania
and Kenya's conservation of the Serengeti plains, and the
United States and Canada's efforts to protect the sandhill
crane.
But a bird like the red knot, which
summers in the Arctic and winters in Tierra del Fuego, the
southern tip of South America, stopping along the way to
refuel in North and South America, will require an unprecedented
level of cooperation.
It is, Dr. Wilcove writes, a worthy
fight: ''It all adds up to one of the most daunting yet rewarding
challenges in wildlife conservation.''
No Way Home The Decline of the World's Great Animal Migrations.
By David S. Wilcove. Island Press. 256 Pages. $24.95 |
