Sea ice changes may impact spectacled eider migration
Last Thursday, Dr. Dan Rizzolo of the U.S. Fish and Wildlife Service gave a Strait Science talk about his work with spectacled eiders, the distinctive sea duck unique to Western Alaska and Chukotka. His work shows that dramatic changes in sea ice may be disrupting the ducks’ annual migrations.
Most spectacled eiders spend their summers breeding along the coasts of Siberia and the North Slope of Alaska, with some breeding populations in the Yukon-Kuskokwim Delta region. During the winter, though, they flock to the sea just south of St. Lawrence Island, where they dive for clams through open leads in the sea ice.
All of the world’s spectacled eiders congregate in the same relatively small area for the winter. Winter flocks can have over 100,000 individual birds, or more than a third of the world population, Rizzolo said.
As ice dynamics shift as a result of climate change, the eiders’ winter haven may be under threat. While it’s not clear exactly how much the birds rely on winter ice, the cascading effects that the loss of ice has on the ecosystem could be devastating.
“The rate of decline of sea ice in the Arctic is going a lot faster than what the models have predicted,” Rizzolo said. “If you follow the current trend out into the future, we will be looking at an Arctic that is ice-free in the summer in the next 20 or 30 years, rather than the next 100 years. So, the future is now.”
Unlike polar bears or ice seals, spectacled eiders don’t rely directly on the ice for hunting or breeding. But Rizzolo said the ice is still critically important. For one, it provides a place to rest while the birds digest their food, so too little ice could cause them to die of exhaustion as they spend their whole winters swimming.
Seasonal ice also has effects throughout the marine ecosystem and its disappearance could impact the clams that the ducks eat in the winter. Spectacled eiders are currently listed as “threatened” under the Endangered Species Act, meaning their numbers aren’t decreasing yet, but they’re at risk of decreasing in the near future.
To better understand these unique birds, Rizzolo and a team of wildlife veterinarians caught 39 individual birds in the spring of 2018 and surgically implanted them with satellite trackers. The trackers broadcast their location every two to six days and gave the scientists a detailed picture of where the birds were traveling.
The trackers are big – about the size of a deck of playing cards – but Rizzolo said they didn’t negatively affect the birds in any drastic way. He admitted that some studies have suggested that the trackers hurt birds’ survival in the long term, but said the internal trackers were still better than an external tag or harness.
“Their feathers are really important for staying warm, so if you put anything on the outside of an eider that disrupts its feathers, it’s a lot like putting a big hole in your down jacket, and during the winter they can’t handle it” he said. “Internal transmitters don’t cause that problem.”
The scientists then tracked the birds for the following year, following where and when they migrated. By November, they had all made it from their breeding grounds to their wintering area south of St. Lawrence Island.
Even though there was no sea ice there at that point, Rizzolo said the ducks got along by resting on the southern coast of the island and spending much of their time at sea. They stayed concentrated there through December and January, which was expected.
But then in February, a few of the birds started flying north again, reaching the Bering Strait and the northern coast of Chukotka much earlier than they’re usually observed there. In March, a few more birds followed, and eventually the rest came north with the arrival of spring.
Rizzolo added that the variation between individual eiders was interesting. Instead of traveling together in a big flock, different birds took different strategies, with some migrating north much earlier than usual and others sticking to their traditional timeline.
A number of factors could have caused some of the birds to take off early, but Rizzolo said climate was probably a major reason. That winter saw relatively low ice cover and consistent southern storms, which could have driven the birds north early.
“Those more northern eiders are within their typical range, they are just not going there at the usual time of year,” he said. “This movement was enabled by low ice cover caused by consistent southerly winds.”
The data suggests that eiders are influenced by the climate, but to what extent are they in danger of climate-driven extinction? More data is needed to answer that question, Rizzolo said, but historical observations of breeding colonies can offer some insight.
In an average year, about 78 percent of spectacled eiders survive the winter and return to their breeding grounds, he said. In the 23 years of observations collected by USFWS, that survival rate has been lower during years of both high and low ice.
Rizzolo said this may suggest a “Goldilocks” situation, where the birds need an intermediate amount of ice to survive. Too much and there aren’t enough open leads for them to dive through. Too little and there aren’t enough floes for them to rest.
He added, though, that unusually low ice in their core wintering area is a relatively new phenomenon, so it’s still not totally understood how low ice will affect them in the long term.
He also added that observations from residents of St. Lawrence Island and other communities around the region will be critical to protecting these unique birds. The wealth of knowledge held by Indigenous communities serves as an important complement to USFWS’s satellite tracking data and is important to create a complete picture of spectacled eiders’ lives.
He encouraged any regional residents observing unusual behavior in spectacled eiders to contact him at daniel_rizzolo@fws.gov.