Epic migration leads caribou to same areas to give birth every spring
From: University of Cincinnati
February 8, 2023 -- Caribou
have been using the same Arctic calving grounds for more than 3,000 years.
Female caribou shed their antlers within days of giving birth, leaving behind a
record of their annual travels across Alaska and Canada's Yukon that persists
on the cold tundra for hundreds or even thousands of years. Researchers
recovered antlers that have sat undisturbed on the arctic tundra since the
Bronze Age.
Female caribou shed
their antlers within days of giving birth, leaving behind a record of their
annual travels across Alaska and Canada's Yukon that persists on the cold
tundra for hundreds or even thousands of years. Researchers recovered antlers
that have sat undisturbed on the arctic tundra since the Bronze Age.
"To walk around
the landscape and pick up something that's 3,000 years old is truly
amazing," said Joshua Miller, an assistant professor of geosciences at the
University of Cincinnati.
He has been leading
summer expeditions to the Arctic National Wildlife Refuge since 2010, using
rafts to navigate remote rivers to search for caribou antlers exposed on the
tundra.
"We think about
having to dig down into the soil to find that kind of ecological history, but
on the Coastal Plain, the vegetation grows extremely slowly," Miller said.
"Bones dropped by animals that lived dozens or even hundreds of
generations in the past can provide really meaningful information."
The study demonstrates
how important the area is for an animal that native Alaskans and Candians still
depend on for sustenance, even as energy companies seek to exploit oil and gas
resources in this protected area.
The Biden
Administration in 2021 suspended drilling leases in the Arctic National
Wildlife Refuge, the largest tract of undeveloped wilderness in the United
States.
"We know this
region of the Arctic National Wildlife Refuge has been an important area for
caribou for millennia," Miller said. "That should give us pause on
how we think about those landscapes."
The study was published
in the journal Frontiers in Ecology and Evolution.
Barren ground caribou
undertake nature's longest overland migration, traveling as far as 800 miles
each year to reach their spring calving grounds in the Arctic National Wildlife
Refuge and Canada's Ivvavik National Park. The largest herd in this area, named
for the Porcupine River, numbers in the hundreds of thousands of animals.
Scientists think
caribou use these areas because they have fewer predators and offer seasonal
vegetation near places where they can avoid the worst of the mosquitoes.
"The mosquitoes
are horrible," Miller said. "You get swarmed -- literally covered in
them. They can do significant damage to a young calf."
Whatever the reason,
the antlers they leave behind provide a physical record of their epic yearly
travels that researchers can unlock through isotopic analysis.
Caribou antlers, like
those of elk, deer and moose, are made of fast-growing bone that the animals
shed each year and regrow the following year.
"It is amazing to
think that the oldest of the antlers found in our study were growing
approximately the same time Homer was penning 'the Iliad' and 'the
Odyssey,'" study co-author Patrick Druckenmiller said.
He is director of the
University of Alaska Museum and professor of the Department of Geology and
Geophysics at the University of Alaska Fairbanks. Eric Wald from the U.S. Fish
and Wildlife Service also co-authored the study.
The antler surveys in
the vast expanse of the Arctic refuge require meticulous logistical planning,
Miller said. Small planes deposit researchers and their gear deep in the
interior, where they have to be watchful for grizzly and polar bears. They
pilot rafts to the Beaufort Sea, conducting a grid search of suitable caribou
habitat identified in advance using aerial photography.
"We search for
antlers along old river terraces, walking back and forth, covering every inch
of habitat to find those ancient treasures," Miller said.
While male caribou
antlers span four feet and weigh more than 20 pounds, female caribou antlers
are much smaller. The antlers contain nutrients such as phosphorus and calcium
that are important to plants and animals.
The dropped antlers
create "nutrient sinks," which could have a profound effect on the
area's vegetation. Miller said the caribou's migration serves as a nutrient
"conveyor belt" that might even draw caribou back to reap the
benefits of this fertilizer in a reinforcement loop.
Caribou and other
mammals are known to chew on dropped antlers for their valuable minerals. This
could be an important dietary supplement for new caribou moms.
"We'd like to know
to what degree this conveyor belt influences why caribou are going there in the
first place," Miller said. The study was supported by the U.S. Fish and
Wildlife Service, the National Geographic Society, the National Science
Foundation, the Wildlife Society and the UC Office of Research.
Miller said the Arctic
is warming faster than other parts of the globe. Parts of the Arctic that were
once barren tundra are sprouting new spruce forests.
"We were in Arctic
Village this summer, just south of the calving grounds, talking to elders about
the changes they have seen," Miller said. "Where once it was open
tundra, large stretches of this barren ground are now full of trees everywhere.
What will happen to the barren ground caribou as this habitat gets converted
into forest?"
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