Originally published in The Economist.


Tern limits

A small tragedy is occurring off the coast of Maine

Aug 31st 2013 | CAMBRIDGE, MASSACHUSETTS | From the print edition

THEY put in 55,000 flyer miles a year, more than any other bird. In a 30-year lifespan that is the equivalent of three round trips to the moon, just to lay one or two eggs. Yet Arctic terns are not as tough as all that. In recent years their numbers have declined by more than 40% at their breeding grounds off the coast of Maine. Similar falls have been reported in the Netherlands and Iceland.

For the past 30 years, workers like Linda Welch at the Maine Coastal Islands National Wildlife Refuge have been trying to restore local seabird populations on islands taken over by predatory seagulls. Arctic terns had been increasing until about five years ago. Then they began tailing off, dropping from 4,224 pairs in 2008 to 2,467 in 2012.

Lack of food appears to be the reason. The birds forage for herring and other small fish, and may face competition from commercial fishing boats. Climate change, meanwhile, may be causing the fish to swim to colder waters elsewhere (see article). Some researchers think the changing climate may be disrupting the food chain in the birds’ winter destination, Antarctica, leaving them too weak to breed in Maine.

The shortage of fish prompted 3,500 Arctic and common terns to abandon their nests on Machias Seal Island, once the largest tern colony in the Gulf of Maine, from around 2006. Last year they bred on just four of the 50-odd islands in the refuge. Without herring or hake to feed their chicks, desperate terns may resort to larger butterfish. “They can’t swallow them, so the chicks slowly starve to death with 20 butterfish surrounding them,” says Ms Welch.

Other migratory seabirds, such as Atlantic puffins and razorbills, face similar problems. Hundreds have starved to death and washed ashore from Florida to Maine. They are useful, if sad, indicators of the health of the oceans, as fish eaten by the terns also sustain species important to people, such as cod and tuna. Gradually, the troubles of the terns are likely to ripple up the food chain.

From the print edition: United States