Searching Boston Harbor Islands for the link to sea duck die-offs
Several hundred, sometimes thousands, of dead common eiders have been found every fall in recent years on the shore of Cape Cod’s Wellfleet Bay. Since 2006, the U.S. Fish and Wildlife Service estimates at least 6,000 of these sea ducks have died at Jeremy Point and other locations along the Cape.
Concerned for the cause of these annual die-offs–and for how other wildlife and perhaps even people might be affected–a group of researchers has come together to study the problem. The investigation has taken us as far north as eastern Canada, and as far south as Rhode Island. It’s led us right back to the Boston Harbor Islands.
“We are worried about the possibility of a population decline due to consecutive years of large losses of adult breeding-age birds,” said Service migratory bird biologist Chris Dwyer. “We’re looking into the source of the die-offs and the role of the recently discovered Wellfleet Bay virus. We–and visitors and residents to the Cape–are wondering what these birds are being exposed to, and is there a connection to the overall health of Cape Cod Bay?”
Last week, researchers from our agency, USGS, University of Pennsylvania, USDA, Biodiversity Research Institute, National Park Service, and Massachusetts Department of Conservation and Recreation and Division of Fisheries and Wildlife continued the investigation with common eider work in the Boston Harbor Islands.
“Eiders represent a group of sea ducks that serve as a barometer of coastal ecosystem health,” he said. “Cape Cod winters large numbers of eiders, and many people are familiar with them and enjoy healthy populations. We need to determine the cause of mortality and the potential implications of this newly described virus to eider populations.”
Here’s what we know:
- What’s dying? Eider die-offs in Wellfleet Bay have been occurring since at least 1998, and since 2006, at least 300 to 500 ducks have died each year, mostly in the fall.
- What might be the cause? In 2007, a staggering 3,000 dead were found, mostly females, between August and October. From the tissues of five dead eiders that year, researchers from the USGS National Wildlife Health Center isolated an enveloped RNA virus. In 2010, the virus was clarified by the Southeastern Cooperative Wildlife Disease Study and understood to be a newly identified virus, found nowhere else at the time, and it was named the Wellfleet Bay virus. We’re confident the virus has some role in the die-offs.
- What is transmitting the virus? The genetic makeup of the virus suggests it comes from an avian soft-bodied tick that we have not found. However, we’re not ruling out other possibilities. Since these are sea ducks, we expect a tick would affect females that spend time on the islands nesting.
- Where is it coming from? We started sampling birds in 2011 for this virus. When we looked in Nunavut, Quebec, Nova Scotia, Maine and Rhode Island from 2011-2013, the blood serum of sampled eiders showed that less than 5 percent were positive for the virus. In Massachusetts (the Harbor Islands and Wellfleet Bay), an average of 33 percent of sampled eiders were positive for the virus. In 2012 in particular, a startling 95 percent of sampled eiders in the islands tested positive.
- So is it just the birds from the Harbor Islands going to Wellfleet Bay to die? No. The islands birds number less than 400, so they cannot be the only birds making up the die-offs. Some of the birds leave the Islands in the summer to regrow their flight feathers. Through satellite transmitters, we are determining if most of the eiders breeding in Boston Harbor leave to do that, if they stay in Massachusetts or depart for northern areas such as Maine or Nova Scotia (and potentially spread the virus). Either way, when they show up on the other side of the Cape Cod Bay in the fall, we have large die-offs from the birds that stop in Wellfleet Bay.
- What did we do this week? Researchers used mist nets to capture eiders off the shore of the islands and used large hand nets (called dip nets) to capture females nesting on the islands. They placed identifying bands around their legs, and took blood, tissue and feather samples for processing. This week, 38 eiders received leg bands, and 10 males and 9 females of that group were fitted with satellite transmitters so that we could get an idea of where these birds go from the islands. Last year, we put out 12 satellite transmitters–half on males and half on females. This year, we recaptured a satellite-marked female from last year and a female that we banded in 2012. We also took soil samples to process for parasites. We will get results from samples in a few weeks, and we’re looking forward to seeing if the two recaptured females will test differently (positive/negative) for the virus this time. MADCR provided vital logistical support, access and collaboration to pull off this work.
- What’s next? We plan to return later this year–when the die-offs usually occur–to compare the samples from these ducks to those that come to Wellfleet Bay in the fall.
“The overarching question is, how do we go from Boston Harbor nesting females in the spring with high exposure to this virus to a different area across the Bay in the fall with a die-off of mostly males that are positive for this virus?” Dwyer said. “The die-off events have proven to be far more complex than expected–what is the geographic source of eiders involved in these mortality events, how widespread may the virus occur, what is the potential route of virus transmission among eiders, and is there evidence of previous exposure to the virus and subsequent recovery among healthy eiders?”
Check out the story from The Boston Globe.