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| Enlarge ImageDead eider ducks litter the beach into the distance. The large sea ducks have suffered repeated mortalities on Cape Cod in the last few years, and researchers from several organizations are working to find the causes. (Photo by Jim Canavan, Woods Hole Oceanographic Institution) |
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| Enlarge ImageWHOI biologist Michael Moore and research assistant Andrea Bogomolni select an eider duck to examine during one of the duck die-offs on Cape Cod. (Photo by Jim Canavan, Woods Hole Oceanographic Institution) |
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| Seabird ecologist Julie Ellis spends much of her time studying birds and bringing together citizens and scientists to improve the condition and prospects of marine bird species. Ellis is the coordinator of SEANET, the Seabird Ecological Assessment Network, at the Tufts University Cummings School of Veterinary Medicine. (Photo courtesy of Julie Ellis, SEANET) |
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| Enlarge ImageWHOI biologist Michael Moore collects ducks to bring back to the lab for a full necropsy to help determine the causes for several eider duck die-offs that have occurred since 2006 on Cape Cod. (Photo by Jim Canavan, Woods Hole Oceanographic Institution) |
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| Enlarge ImageWHOI biologists Andrea Bogomolni and Michael Moore work together to take samples from an eider duck right on the beach, hoping the rapid sampling can provide clues to the mysterious deaths. (Photo by Jim Canavan, Woods Hole Oceanographic Institution) |
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| Enlarge ImageAt the end of this collecting trip, Bogomolni carefully packs samples taken from dead and dying eider ducks, which will be sent to laboratories to be analyzed for toxins or infectious organisms. (Photo by Jim Canavan, Woods Hole Oceanographic Institution) |
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| Enlarge ImageA trio of healthy eider ducks. (Photo by Jim Canavan, Woods Hole Oceanographic Institution) |
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| Enlarge ImageCape Cod, Mass., is on the Atlantic flyway for migrating birds, and indicated are areas where eider ducks frequently congregate. (Map image courtesy of NASA) |
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Andrea Bogomolni was in a skiff near shore when she saw the ducks
in October of 2007: “It was surreal,” the biologist remembered. “You
could see hundreds of lifeless brown, black, and white lumps on the
beach, a foot apart from each other. It was just like they fell out of
the sky and dropped dead.”
Seabird ecologist Julie Ellis had already heard about the ducks dying
on Cape Cod, but it didn’t prepare her for the sight. Hundreds of
common eider ducks were cast ashore, bedraggled and dead, at the wrack
line, where the receding tide leaves debris, “lying just one after the
other,” she said.
Since 2006, about 2,000 of the sea ducks have died in five mass
mortalities on Cape Cod’s beaches. Scientists and conservationists are
rallying to find out why.
Ellis is the director of the Seabird Ecological Assessment Network
(SEANET), based at the Tufts University Cummings School of Veterinary Medicine, which
brings together groups of academic and government researchers, along
with citizen scientists, in efforts to identify and mitigate threats to
marine birds throughout the Atlantic coast of North America. The
mystery of the eider duck die-offs has pulled together Ellis,
Bogomolni, a biologist at Woods Hole Oceanographic Institution (WHOI),
WHOI biologist Michael Moore, and other researchers at Tufts
University, Cape Cod National Seashore, Cape Cod Stranding Network,
U.S. Fish and Wildlife Service, and the New England Aquarium. An
unusual partner, the hunters’ association Ducks Unlimited, has also
joined in the effort to find out what’s killing the eiders.
Collecting specimens and testing suspect causes, the researchers have
found and verified one potential cause, but it doesn’t explain all the
deaths. There may be multiple causes, ranging from parasites to
invasive species, bacteria, viruses, toxic algae, and pollution.
Eiders down
Eiders are northern sea ducks, known for their beauty and exquisitely
fine down feathers, which were used for centuries to make comforters
known as “eiderdowns.”
Common eiders are the largest ducks in North America, nearly 2 feet
long and 4 pounds. They breed in summer on far northern coasts in
Alaska, Hudson Bay, Canada, and Maine. They migrate south in autumn and
spend winters along coasts south of their summer homes. Many thousands
of eiders migrate to spend winters in southern New England, especially
on Cape Cod Bay, where both birders and hunters appreciate them.
Eiders have a tough time. Hunted nearly to extinction once, they
rebounded, only to see more problems in the last three decades. Common
eider populations have declined sharply in some areas (the Pacific and
the Arctic) since the 1970s. Some experts believe that Common Eiders
are also declining on the Atlantic coast of North America. Hunting,
food availability, parasites, the condition of reproductive females,
high mortality rates among ducklings, and diseases all may be
contributing to the drop.
People have seen and reported mass eider deaths before. On Cape Cod
beaches, mortalities have been annual or semi-annual since at least the
1980s, but this year die-offs seemed to happen more often.
Mussels to crabs to worms
In the early spring of 2006, an eider duck die-off occurred in
Wellfleet, Mass. Tufts veterinary students discovered the ducks were
infected with intestinal parasites known as acanthocephalans
(“spiny-headed worms”). Such parasite infections are common in sea
ducks, and these worms cause eider mortalities in other regions.
The case seemed simple enough: The evidence pointed to a direct link
between seasonal parasites and duck deaths.
Cape Cod is a major overwintering site for eiders, whose favorite prey
is blue mussels. But populations of the bivalves may have declined in
recent years. “If eiders can’t get mussels,” Ellis said, “they’ll
eat snails and crabs—mainly Asian shore crabs and green crabs, because
that is what’s available.”
These
two crabs, both non-native species that have been introduced to Cape
Cod, have increased in numbers. Crabs are the parasitic worm’s
intermediate host. “The worm’s juvenile form lives inside crabs, the
eider eats the crab, the worm embeds in the eider’s gut, grows and
breeds, shedding eggs in the duck’s waste,” Ellis said.
When an eider duck eats a crab, it gets a nasty hitchhiker along with
dinner. The parasites can occasionally reach numbers that block their
host’s gut so that no other food can be absorbed.
“Lots of eiders in the die-off had guts that were full of these
acanthocephalan parasites,” Ellis said. “The ducks were emaciated,
starving.”
The trail gets complicated
Another large die-off happened in October 2006, and this time the
situation was more complicated. Ellis and Moore went to Wellfleet and
Great Island, counted 300 to 400 dead birds, and collected many. Tufts
veterinary students and Bogomolni performed necropsies and sent samples
for analysis to the National Wildlife Health Center in Madison, Wisc.
“We can’t pin down a cause of this die-off,” Ellis said. Many birds
were emaciated, but not all—in fact, some, Bogomolni said, “were
robust, but seizing uncontrollably.” Some had the parasites, some did
not. The researchers ruled out bacterial infections, bird flu, and West
Nile virus. They tentatively concluded that the ducks died of a viral
infection, but are still trying to isolate a virus from the samples.
Unexpectedly, yet another mortality occurred in summer 2007. It’s
unusual to see eiders in bad shape on the Cape in summer, said Ellis.
The dead birds were almost all females.
Ellis went out with Moore again to collect dead and dying ducks. They found them on beaches full of beachgoers.
“It could present a public health issue,” said Ellis. Like many marine
mammals and seabirds, these eiders harbor bacteria known to cause
infection in humans, said Bogomolni. She is currently studying zoonoses
(how disease organisms in animals could spread to humans), in
collaboration with Moore, Ellis, WHOI biologist Rebecca Gast, Mark
Pokras of Tufts University Veterinary School Wildlife Clinic, and Katie
Touhey of the Cape Cod Stranding Network.
“But we still know no cause of death for this event,” Ellis said.“It’s not bird flu, or any particular bacteria.”
Susanna Corona from the New England Aquarium, working with SEANET,
collected samples of crabs, water, and fish from Wellfleet for analysis
by Jim Haney, a scientist at the University of New Hampshire who
studies toxins produced by harmful algae called cyanobacteria.
Cyanotoxins were found in nearby Rhode Island waters during the summer
of 2007. Other samples are being tested for botulism toxin, the
dangerous poison sometimes produced by bacteria in improperly canned
food.
An unusual ally
The most recent die-off happened in October 2007. This time adult
male ducks died. Males migrate first in the fall, then females, said
Ellis—offering a clue that the timing may be a factor in whatever
killed the ducks.
Bogomolni and Moore collected 15 dead eiders for SEANET. They
euthanized five moribund ducks to send to the National Wildlife Center
as unfrozen samples, in case freezing the samples might be destroying
some evidence of a cause.
“And again we are not solving it,” said Ellis, “and it’s driving us
crazy! Because we’re so annoyed that we can’t identify the cause, we
decided to do something unusual”—get in touch with duck hunters.
“No one knows what is a normal state of health for wild birds,” she
explained. “Jack Renfrew, from the waterfowl and wetlands conservation
organization Ducks Unlimited, said, ‘Well, it’s hunting season, and we
shoot eiders anyway, so we could give you some healthy eiders’ ” to
examine.
“Some might think that’s not the group to go to, to find out how to
keep ducks healthy,” Ellis said, “but people don’t always realize how
active hunters are in all kinds of conservation efforts. They really
care about the ducks.”
Researchers and hunters went to Great Island; the hunters hunted and
contributed eiders, and scoters (another sea duck) for comparison.
“Jack Renfrew said, ‘If they’re eating same thing and only eiders get
sick, why is that? If they’re not eating same thing, we can find the
difference in their food source’ from looking at gut contents,” Ellis
said. “We thought it was a great suggestion.”
More volunteers on the case
The hunted eiders looked in good condition, Ellis said. Sarah
Courchesne, a Tufts veterinarian who necropsied the dead eiders, and,
curiously, found as many if not more acanthocephalans in the
gastrointestinal tracts of the hunted birds, compared with the birds in
the die-off. That suggests that the parasites may not be the primary
cause of these die-offs.
The researchers will send tissue for analyses, “but testing and
culturing samples is very expensive,” Ellis said. “Histology is pricey,
but it will tell us more at the tissue level, about the difference
between the hunted and sick eiders.”
Ellis is also working with the students, who are monitoring eider
numbers via a video camera on Nantucket (put in place and monitored by
researchers at the University of Massachusetts, Boston) and looking for
the parasitic worms in Asian shore crabs that Ellis collects. And she
is bringing the science and the mystery to Quincy and Dorchester
teachers and their classes, via the Centers for Ocean Sciences
Education Excellence program offered through UMass Boston.
To overcome the difficulties of getting accurate counts of dead eiders
on Wellfleet beaches, Ellis recently put out a call for volunteers to
aid with SEANET’s efforts to monitor the health of Cape Cod seabirds;
she offered volunteer training for interested citizens at the
Massachusetts Audubon Society’s Wellfleet Wildlife Sanctuary in
January. Among the things volunteers will do: walk Cape Cod’s beaches,
looking for dead ducks.
—Kate Madin
This research is supported through SEANET, the Bernice Barbour Foundation, and the NOAA Oceans and Human Health Initiative.
Posted: February 7, 2008 [top] |
