Tiny Harpswell island home to thousands of once-rare terns — and 2 hardy scientists

As they hunt for fish, common terns are a delight to behold.

These smallish gray-and-white birds with black caps and orange beaks swoop low over the water. Stopping to hover, a tern will suddenly plunge into the water, emerging moments later with a small herring hanging from the side of its beak.

Acrobatic flyers and efficient hunters, these birds seem to be masters of their world. In fact, they need a lot of help to prosper.

In the late 1980s, there were fewer than 1,000 nesting pairs of common terns in the entire state. While the species was not listed as threatened or endangered by either the federal government or the state, the common tern was definitely not common here. Since then, the population has rebounded dramatically, to about 11,000 nesting pairs. Much of the credit belongs to the National Audubon Society’s Seabird Institute. On the seven Maine islands managed by the Seabird Institute, the common tern population has risen in a few decades from just a few hundred pairs to about 9,000 pairs today.

A significant part of the Seabird Institute’s work takes place on Jenny Island in Harpswell. This 2.7-acre bit of rock lying about 2 miles south of Cundy’s Harbor is owned by the Maine Department of Inland Fisheries and Wildlife. The Seabird Institute has managed its bird population since 1991.

One of two common tern nesting colonies in Casco Bay, the island was home this summer to almost 1,900 nesting pairs. That means Jenny Island alone accounts for about 17% of the entire common tern population in Maine. For the last two summers, the island also hosted 17 pairs of roseate terns, which are listed as endangered in Maine. During the breeding season, April 1 to Aug. 31, the public is not allowed to visit the island.

During this year’s season, two researchers with the Seabird Institute resided on the island. Ben Becker, a 2017 graduate of the University of Maine with a Bachelor of Science degree in zoology, has the title of island supervisor. This summer marked his fourth year on the island. For Sophie Mollo, the research intern, this was her first year. She received her Bachelor of Science in zoology in May from the University of New Hampshire.

Their responsibilities include protecting the birds from predators and conducting research. To say it is a demanding job is an understatement.

They arrive on the island when the birds do, in May, and remain until the birds leave, in August. Their sleeping quarters for three months are compact tents, of the kind favored by backpackers, pitched on wooden platforms. There is no running water, so their toilet is an outhouse with a composting toilet, and their bathing facilities are the sea and a hand-held shower.

They have a cook shed where they prepare their meals on a propane stove. There is no fridge, only coolers. Their water supply consists of six 5-gallon jugs. Every three weeks, they get resupplied from the mainland by the Seabird Institute, which is based in Bremen. That means their ice has melted and the fresh food has been consumed long before new supplies arrive.

“We do fairly well as far as the cooking goes. I like to make a lot of curry, fajitas and tacos,” Becker said. “We harvest mussels when there’s not a red tide alert.”

The weather can create discomfort and occasional fear.

The low-lying island is treeless, so there is nothing to impede the winds. In August of 2020, a tropical storm packing 50-mph gales passed through.

“That was the most scared I’ve been sleeping,” Becker said.

But what would be hardship for most people, Becker and Mollo take in stride.

All in all, “it’s almost like glamping,” Becker said.

Mollo was even more upbeat. “It’s really nice,” she said. “I like it.”

What does she like best? “Maybe the view. There’s always a different sky.”

The work itself is challenging and sometimes frustrating. The list of predators they try to deter includes herring gulls and great black-backed gulls, great horned owls, black-crowned night herons, peregrine falcons, crows and ravens.

This year, perhaps the greatest predator threat to the chicks was a black-crowned night heron. The terns can defend against other birds during the day by rising en masse and swarming the invaders until they leave. Against the night herons, the terns are largely defenseless, since the terns have poor night vision, while the herons (as their name implies) hunt at night.

How did they resolve the problem? “The answer is, we haven’t,” Becker said.

Becker is authorized to kill predators that pose a threat and has a .22-caliber rifle for that purpose. Before resorting to the rifle, “we try to exhaust every nonlethal option,” he explained.

In this case, he concluded the heron was preying primarily on weaker chicks. “The small chicks wouldn’t survive,” he said, so he decided the best course was to tolerate the heron.

Predator deterrence is important for the birds’ day-to-day survival. In the long term, the fate of the birds may hinge on the research being done by the Seabird Institute. Becker’s and Mollo’s typical workday is mostly spent collecting data supporting that research.

The two regularly check nests in five “productivity plots.” This year, the smallest of the plots had four nests, while the largest contained 30. The plots are surrounded by screen fences about a foot and a half high — too tall for the flightless chicks to surmount. The plots provide the researchers with a window into how the rest of the chicks on the island are faring.

Each plot is visited every other day. Early in the season, the researchers count the number of nests, later the eggs and then the hatchlings. As the season progresses, they note the number of chicks that die — starvation is a big killer. They record the development of each remaining chick by carefully weighing it in a bag suspended from a hand-held scale. They also measure each bird’s wing length.

It sounds simple enough, but the parents of the chicks often make evident their displeasure with the intrusions in unpleasant, even painful ways. They will fly low over the researchers, defecating on them and pecking at their heads.

The hat Becker wore during these nest checks bears witness to the aggressiveness of the parents. They pecked it so forcefully and so often that they shredded the fabric on his hat’s crown.

Some birds are more strategic in their attacks than others. One repeatedly attacked Mollo. “Her hand had holes in it,” Becker recalled.

“I’d be holding up a bag to weigh a chick,” Mollo recalled. “There was blood all over everything.”

This bird had learned to target flesh.

“I know this one. We go way back,” Becker said. “This individual was smart. It went for skin.”

Another project aims to determine the kinds of fish the terns are feeding their chicks and where they catch them. Becker and Mollo conduct this research from inside the island’s three blinds — sheds about the size of an outhouse with viewing slots cut into their sides.

The researchers record the direction the birds go to look for food and the kind and size of fish they bring back. That means the researchers must be able to identify the species of a tiny fish hanging from a bird’s beak as it flies by. The possibilities include herring, hake, pollock, bluefish, saury, butterfish, sticklebacks, or even the occasional lobster larva.

“It can be difficult,” said Mollo.

The Jenny Island data gathered over the years is encouraging. The number of common tern nesting pairs has climbed steadily in the last two decades. The 2,000-plus pairs recorded in 2021 was a record. The figure for this year was down slightly to 1,899.

Breeding success seems to be holding up. In 2021, approximately one chick survived for every two nests, not a great number. This season, the rate rebounded. Initial estimates indicate that, on average, more than one chick per nest survived, Becker said.

Don Lyons is director of conservation science for the Seabird Institute. He says the data from Jenny Island is consistent with what he is seeing on the other islands managed by the Seabird Institute. “Here in Maine, the common tern population is robust and growing,” he said.

That said, longer-term threats remain.

For example, the populations of fish on which the birds depend could decline. “One thing we’re particularly interested in is what the birds eat,” Lyons said.

That information is not just of importance to advocates of birds. It also has implications for commercial fishermen. While terns prey on herring when they are small, commercial fishermen catch them for lobster bait when they are adults.

“Birds give us a preview of what’s coming. They can be a really important data stream for managing fisheries sustainably,” Lyons said.

The advent of offshore wind projects is a major concern. If research can identify where the birds concentrate their fishing efforts, it might be possible to make those critical habitats off-limits to wind farms.

Back on Jenny Island, Becker is understandably proud of the work he and Mollo are doing there. They are doing their part and he hopes others will do theirs. “If people would like to help these birds, the best thing they can do is respect their space,” he said.

John Gormley is a retired journalist who lives in Cundy’s Harbor. His interests include fishing, tennis and gardening.