Scientists team up to solve mysteries about dwindling Aleutian tern population

Yakutat, a coastal community on the northern edge of Southeast Alaska’s temperate rainforest, is something of an Alaska refuge for a bird that may be on the brink: the Aleutian tern. Its wide, sandy beaches – and particularly, a peaceful site called Blacksand Spit — holds Alaska’s biggest concentration of Aleutian terns, a long-distance migrator that is sometimes overshadowed by the more famous Arctic terns.

That makes Yakutat a center for study of a bird species about which there remain many mysteries and unanswered questions.

Prompted by some troubling signs, including a 2015 study that calculated a 93% population decline in Alaska since 1960, scientists in Yakutat and elsewhere and from different government agencies and academic institutions have been collaborating as a working group to better understand the birds and what is causing their problems.

“I absolutely think the Aleutian terns are in trouble,” said Heather Renner, a U.S. Fish and Wildlife Service biologist who was lead author of the 2015 study and a follow-up 2021 study that warned that if declines at four key colonies are representative of conditions in other parts of the breeding range, “implications for the global population would be dire.”

There are many gaps in data, but signs are unmistakable, said Renner, who works out of the Alaska Maritime National Wildlife Refuge headquarters in Homer. “We are watching colonies disappear,” she said. 

Aleutian terns breed exclusively in Alaska and some neighboring parts of the Russian Far East. The International Union for the Conservation of Nature, which classifies Aleutian terns as “vulnerable,” estimates the world population totals 31,000. The Alaska population, Renner said, may be as low as 5,000.

Of that Alaska population, the Yakutat colony is dominant, with possibly up to 2,000 birds, said Susan Oehlers, U.S. Forest Service wildlife biologist who has been studying Aleutian terns for several years.

Term research currently underway in Yakutat includes use of acoustic devices called “songmeters,” as well as old-fashioned point counts to try to better quantify the colony size. Associated monitoring is underway in other parts of Alaska, such as tagging work being done in Nome by scientists from Oregon State University, the Alaska Department of Fish and Game and their partners.

It is all leading to what is intended to be a statewide population survey that will examine sites that are known to have been used in the past for colonies as well as sites that might hold suitable habitat for colonies that have yet to be identified. That survey, likely to continue over multiple years, could start as early as 2023, Renner and Oehlers said.

To help develop a consistent methodology for statewide use, collaborating organizations are conducting a pilot project that is using aerial surveys to try to count Aleutian terns in the Bristol Bay region, Renner and Oehlers said.

Recent work has provided some other important information.

Thanks to tagging work, scientists in 2018 concluded that Aleutian terns spent their winters in Indonesia, Thailand and neighboring parts of Southeast Asia. That means they travel extremely long distances, as do the Antarctic-to-Arctic-migrating Arctic terns.

Since Arctic terns, though much more plentiful, are also suffering a decline, Renner suspects that something is going wrong in the marine environment used by both bird species.

“To me, that points to something like the marine food web,” she said. And that may be setting up Aleutian terns to be weaker when they are at their colonies and therefore more at risk of predation, she said. But for now, those are just suspicions, she said. “The best answer is, we just don’t know,” she said.

Aleutian terns are notoriously difficult birds to study, Renner and Oehlers said.

They nest on the ground, and they are easily spooked by anything – including bird-counting biologists – that they perceive to be predators. “If you walk into a colony, they’ll just walk out and leave,” Renner said. “They flush really easily.”

They don’t always return to the same nesting sites, either.

“The colonies are not necessarily real consistent. They tend to move around,” Oehlers said. “That just makes it really difficult to track the numbers.”

Another challenge is new, the product of international turmoil.

Some key recent research – including Renner’s 2021 study, which used data collected by drone – was done in collaboration with Russian colleagues and within the Russian breeding ground. Such collaboration has ended abruptly, thanks to Russia’s invasion of Ukraine. For the near future, the status of Aleutian terns in Russia may be another subject of mystery to the Alaska scientists.

The situation is discouraging, Renner said. “The two countries make up the whole worldwide population of Aleutian terns,” she said. “The birds aren’t recognizing international boundaries.”