Monday, June 24, 2013

Seabirds Warn of Ocean Change

An Arctic Tern in flight with wings spread

Gulf of Maine (USA) - map

What can 30 years of research and monitoring on Maine seabirds teach us?
That the marine environment is changing fast. That ocean birds may be
failing to adapt. That the scope of few marine threats - from ocean warming
and offshore energy development to competition from commercial fisheries -
could have been foreseen when Maine Coastal Islands National Wildlife
Refuge<>staff began studying
the birds in the early '80s.

The refuge, made up of more than 50 islands in the Gulf of Maine, uses data
from research and monitoring to manage Maine seabird colonies and try to
stem the birds' decline.

Consider the Arctic tern. Its 36,000-plus mile-per-year migration from its
wintering grounds in Antarctica to its Maine breeding grounds is the
world's longest; the little bird makes the equivalent of three round trips
to the moon in its 30-year lifetime. Small light-sensing units called
geolocators have been used to document the distance flown. But over the
last five years, counts of Arctic terns in Maine have dropped by 42
percent, from 4,224 pairs in 2008 to 2,467 pairs in 2012. "There are fewer
pairs of Arctic terns breeding in the Gulf of Maine, and those terns that
do breed are producing fewer chicks. They're doing very poorly," says
refuge biologist Linda Welch.

Similar declines reported by the Netherlands and Iceland suggest that more
than a local factor is to blame. Some researchers suspect climate change is
disrupting the food chain in the birds' wintering grounds. "So it might be
the birds can't find enough food to rebuild their body stores and regain
the energy they need to fly from Antarctica all the way back to the coast
of Maine in good enough shape to start breeding again," says Welch.

Or take the Great Shearwaters that spend summer in the Gulf of Maine.
Satellite tags show the large birds forage across the entire gulf - not
just near the coast, says Welch. She hopes developers will consider that in
deciding where to place proposed offshore wind farms. "Other research
projects have shown that most of the seabirds along the Mid-Atlantic funnel
close to the shoreline. In some cases, they say that once you go beyond
five miles, there are no birds out there. In Maine, that's definitely not
the case." Because ocean topography varies, she says, a study done in one
region may not apply to another.

Bird-tracking devices may also help researchers unravel a mystery: why some
Maine seabirds can't find enough fish to feed their chicks. Arctic terns
forage for herring and other small fish at the water surface; unlike
puffins and razorbills, they can't dive for fish. Machias Seal Island once
hosted the largest tern colony in the Gulf of Maine. But in 2007, a fish
shortage led 3,500 tern pairs to abandon their nests. "They haven't raised
any chicks since," says Welch.

Other Maine colonies are also having trouble finding food to feed their
chicks. "The adult are desperate," says Welch. "They try to bring in other
kinds of fish or invertebrates for the chicks to eat. Sometimes the fish
are too big for the chicks to swallow whole. So the chicks starve to death
with all those fish carcasses lying around them. It's really sad."

While the problem appears worst for Arctic and roseate terns, puffins and
razorbills are also affected. At most colonies, puffins are generally able
to still produce chicks, but often those chicks are smaller and weigh less,
says Welch. "So we don't know: Are those birds going to survive once they
leave the colony? Will they be able to return when they are five to six
years old and breed?"

Marine productivity levels, water currents and water temperature all
influence the distribution of fish. Increased Arctic ice melt could also
affect water chemistry and the location of fish. "It's not an easy
problem," says Welch.

New tracking technology is making some seabird research easier. For
example, nanotags that send data to automated receiving stations let
researchers collect data on bird movement without having to retrieve the
tagged birds - as is required with geolocators.

But interpretation of bird movement patterns, population changes and
productivity rates all rely heavily on visual data painstakingly collected
over the past 30 years. It's not glamorous work. Each summer, seasonal
technicians live on the seabird colonies and monitor the seabirds. Peering
through binoculars, they document how many pairs return to the colony, how
many eggs are laid, how many of those eggs hatch, how often chicks are fed,
and which species of fish are brought to the chicks. Researchers compare
notes with conservation partners in the United States and Canada who are
also monitoring seabird colonies throughout the Gulf of Maine.

"Having a long-term monitoring effort has been critical to our
understanding of changes in productivity and seabird diet," says Welch.
"For example, with the Arctic terns, we had 25 years of population growth.
Now we have five years of population decline. Our management actions
haven't changed. Our predator control actions haven't' changed. So we know
something else has changed. This large collaborative data collection effort
gives us a much better understanding of the system."

For its seabird research, the Maine Coastal Islands National Wildlife
Refuge received a Rachel Carson Award for Scientific Excellence from the
U.S. Fish and Wildlife Service for 2012.

No comments:

Post a Comment