Eider duck populations are declining. Both sides of the border want to know why

Scientists from a United States research institute are gearing up to travel to Grand Manan, N.B., at the end of this month to implant tracking devices in some eider ducks and set them free again.

The hope is that those ducks will someday shed light on why the species is declining in places like New Brunswick, Nova Scotia and Maine, but increasing in others, like Newfoundland and Labrador.

It's something that has puzzled scientists for more than a decade, and while research on the topic has been done before, it has never been done on this scale, said Dustin Meattey, director of the waterfowl program at the Biodiversity Research Institute in Maine.

Officials in Canada and the U.S. are working together on the project. Partners include the Canadian Wildlife Service, Environment Canada, the U.S. Fish and Wildlife Service, Maine's Department of Fisheries and Wildlife and Acadia University.

Together, researchers will capture and tag breeding eiders throughout their range ⁠— the geographic area where a species can be found.

They started with eiders in Maine and Quebec last year. Now, they're moving onto New Brunswick, Nova Scotia and potentially Newfoundland and Labrador, unless there is a later breeding season this year due to snow. If that's the case, Meattey said they'll go there next year.

While location data from the transmitters will help scientists learn more about different distribution patterns, migration routes and types of habitat, Meattey said they're really trying to hone in on the proportion of birds that are breeding. 

Eider ducks are primarily capital breeders, meaning that prior to nesting, females must acquire all the nutrients they need to make their eggs and sit on them, which can take up to four weeks.

"They'll very rarely leave the nest during incubation," Meattey said.

The nesting ducks need their bodies to be strong enough to last the entire period, but if environmental conditions stop that from happening, Meattey said they might just skip the breeding season altogether.

The eiders' primary food source is blue mussels, making areas with large blue mussel beds important, Meattey said. 

That's the reason behind one theory about why eider ducks might be declining: they feed on blue mussels in the Gulf of Maine, which is one of the fastest warming bodies of water on the planet. Meattey said blue mussels have a narrow window of water conditions they can survive in.

"As the waters warm, that affects the distribution of blue mussels, [and] they can't survive as well toward the southern part of their range in the warmer waters," he said.

There are other theories about why the eider ducks might be declining, Meattey said, including the presence of green crabs, an invasive species that moves north as waters warm, which impacts blue mussel beds.