BAR HARBOR — Accompanied by a team of student researchers, John Anderson spent several of his summer days on Great Duck – a small, remote island 11 miles south of the entrance to Frenchman Bay.
The natural history professor at the College of the Atlantic in Bar Harbor travels to the island to study seabirds – gulls, guillemots and Leach’s storm petrels.
This year, some of what he saw was distressing. While gathered on the top of the lighthouse on this island, observers witnessed an aerial attack on seabirds there every 45 minutes.
Bald eagles, their majestic wings spread wide, distinctive white heads and razor-sharp talons, soared in repeatedly to hunt small seabirds. The recovery success of eagles, according to Anderson, is increasingly becoming a threat to seabirds.
These predators, once nearly wiped out in Maine, have made a comeback. “They are having an immediate affect on the decline of seabirds,” Anderson said.
When the bald eagle was adopted as the national symbol of America in 1782, the country had nearly 100,000 nesting birds.
These numbers began to plummet in the 20th century when the raptors were hunted, their habitats were destroyed, and they suffered poisoning with the pesticide DDT, which they were exposed to by feasting on contaminated fish.
In 1967, with only 487 nesting pairs of bald eagles remaining nationally, the species was officially declared endangered.
“We had gotten rid of the predators that were keeping the seabirds out,” said Anderson. “So starting then, there were more seabirds nesting on the islands here.”
The seabird population kept growing until the 1980s, when developments began to benefit the bald eagles. DDT was banned, and conservation efforts were taken to protect the predators.
By 2013, Maine was home to more than 600 pairs of bald eagles. “Once the bald eagles really started to make a comeback, they were looking for food,” said Anderson. “We used to have huge numbers of fish as a food source for the birds; a lot of them have been wiped out.”
The change is salinity and trends in water warming in the Gulf Of Maine, is “getting worse, not better,” and causing the loss of fishes, he said.
With more eagles and fewer fish to feed on, the birds are flying to the remote, rocky islands and raiding the nesting colonies of herring gulls and cormorants.
“We have lost about 40 percent of the herring gulls in Maine in the last 10 years,” said Anderson.
This recovery of bald eagles, he said, and their increasing number of attacks on seabirds, like the ones he has witnessed on Great Duck Island, is the foremost cause of the diminishing seabird population.
Most of the seabirds, he said, nest on the ground and are vulnerable to terrestrial predators such as mink, fox and coyotes. Remote islands offer protection from those dangers. But eagles have added a new dimension.
Human disturbances also are causing the disappearance of their colonies.
Some seabirds are more sensitive than others, Anderson said. Cormorants are extremely vulnerable to disturbance, and “all it would take is for a couple of kayakers to land on the island for half an hour to take pictures at the wrong time of year, and most of the chicks would be killed.”
The “wrong time of the year” is their nesting period, which is typically from mid-May to July. “Real seabirds don’t spend that much time on land,” he said. “Land is for nesting, the water is where they live.”
Due to their sensitivity to terrestrial threats, seabirds nest almost exclusively on islands, and their colonies are often located on relatively remote, inaccessible sites.
Low lying nests recently have come under threat due to the rising sea level.
According to a report published by Anderson in October on the impact of rise in the sea level on the seabirds nesting in Acadia National Park, the level of impact is largely dependent on the shape of an island.
Schoodic Island, located about a mile from Schoodic Peninsula, supports a large number of nesting common eiders, herring and great black-backed gulls and a large colony of double-crested cormorants.
In spite of its relatively large size, the island is likely to be impacted by moderate sea level rise through the loss of key nesting areas.
“When the sea goes up three feet, it’s not going to be Schoodic Island anymore; it’s going to be half a dozen little tiny islands,” Anderson said. “Some of the most important nesting habitats are going to be flooded.”
All these causes are leading to an overall downward trend in seabird population.
Little Duck Island was home to more than a 1,000 nesting gulls in the early 1990s. Two years ago, there were less than 30.
On Thrumcap Island, that population has fallen from “several hundred pairs of gulls to not more than 70.”
Conservation efforts to restore the seabird population are being made by the Maine Department of Inland Fisheries and Wildlife.
Atlantic puffin, great cormorant and Arctic terns are among state-listed threatened seabird species. Federal agencies have acquired seabird nesting islands and work towards habitat restoration and controlling predators, as part of their conservation efforts.
“I love gulls,” said Anderson. “They’re wonderful fliers and are very much part of our whole image of the seashore.”
Their aesthetic beauty and their predilection towards cleaning up garbage are a few reasons why Anderson said that the declining population of seabirds is a cause of concern. “People think of them as a nuisance and not as being something beautiful, so they don’t pay attention. I’m afraid we could lose them without even realizing until it was too late.”