Common Terns

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Common Tern, Sterna hirundo

This blog is an extension of the Peaks Plumage article in the September issue of Peaks Island News.

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Introduction
The Common Tern is a medium-sized tern with a deeply forked tail. Its color pattern is, well, tern-like, i.e., white and shades of gray with a black cap (hat). Against this grayscale background are its striking orange-red feet and the red-orange bill with black-tip. Unlike adults, juveniles and fledglings have an incomplete black cap (a white forehead, perhaps with black flecks; see photo).

Watch for Common Terns in Diamond Pass, and at either end of the Peaks-to-Portland ferry route, feeding close to shore and/or docks. They dart about, searching for small fish and quickly plunge in for attack. Single prey is caught in the bill, after which the tern emerges and flies upward while shaking water from its plumage. It uses its tongue to rotate the prey within its mouth so that it can swallow it head-first within a few seconds of capture. If they are feeding young and fish are abundant, two to four fish may be caught and carried back to the nest without swallowing.

Favorite food items include Atlantic herring, hake, American sand lance, and butterfish. In addition to small fish, terns may take krill, small crabs, lobsters, shrimp, or insects depending on availability. They may catch flying insects up to 60 meters above the sea surface, a feeding strategy called hawking. Other insects (e.g., moths, beetles) are collected directly from the water surface.

Nesting occurs on Maine’s offshore islands, and to a lesser extent on inland lakes; these isolated sites help to protect them from mammalian predators. Although they breed in colonies, colony members don’t always get along. Adults frequently steal fish from each other. Some may form groups (gangs?) to pursue an unsuspecting flying adult carrying a fish. Or they may swoop down to seize a fish from a parent delivering it to its chick.

Common Terns nest primarily on the ground, in a shallow depression in gravel or sand. For decoration of their open nest a departing tern may casually throw a twig backwards over its shoulder. If its partner is not hit by the hurled stick, it may be added to the developing nest.

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The Decline
In 1885 there were 75 colonies of nesting Common Terns along the coast of Maine (some colonies included roseate, arctic, and least terns). Tragically with the advent of the millinery trade (women’s hats) only 32 colonies remained by 1890. Hunting continued into the 20th century, despite legislation passed to protect the birds (Lacey Act 1900 and Migratory Bird Treaty Act 1918) and formation of the National Association of Audubon societies and other conservation initiatives. By 1936, there was a rebound of Common Terns to 6,000 pairs in 25 colonies. But then, by the 1970s, predation by rats, cats, and dogs, encroachment by gulls, and disturbance by sheep pasturing on islands decreased the population to 2095 pairs in 18 colonies. Since those horrific times, restoration projects for Common Terns have increased Maine’s island populations.

The good news is that since 2002 Common Tern colonies have returned to our ‘backyard’. Looking eastward from Peaks Island’s backshore one can see two small islands close together – Outer Green Island and the smaller “Junk of Pork”. They were the site of a thriving seabird colony until 1914, when hunting for the millinery industry brought an end to the colony. Fast forward…

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Recovery
In 2001-2002, Outer Green Island was chosen as a seabird restoration site by the Seabird Restoration Program (now called Seabird Institute) of the National Audubon Society because it is 2.5 miles from any large, forested island (Peaks and Jewel Islands) where predators such as the mink and great-horned owls have easy access. The nesting seabirds were victims for several years to peregrine falcons, which nested on Ram Island Lighthouse. Even so, the numbers of breeding terns increased gradually from one nest in 2002 to 1067 nests in 2011, then to a maximum of 1,994 active nests in 2022. That number has decreased somewhat recently, but those nests are quite active. This year, preliminary data shows that the 1,429 active nests produced an unusually high 1750 fledglings. Though we haven’t kept track ourselves, it does seem like Common Terns are more common this year in waters surrounding Peaks Island.

Currently the Seabird Institute and the Maine Department of Inland Fisheries and Wildlife (who own the island) cooperatively manage this seabird breeding colony, with logistical support from the U.S. Fish and Wildlife Service, Gulf of Maine Program. Outer Green Island is closed to public visitation during the seabird breeding season (April 1 to August 31). As the first terns arrive in early May, so do the Audubon staff members who set-up tents and bird blinds for monitoring and protecting the Common Terns and other nesting seabirds such as Black Guillemot and Common Eider, and, more rarely, American Oystercatcher and roseate tern. Volunteer research assistants leave around the end of July or first of August after seabird chicks fledge.

One other island in Casco Bay – Jenny Island, south of Cundy’s Harbor – was restored for seabirds in 1991. By 1993, this island was the only active tern colony in Casco Bay. But unlike Outer Green Island, predation by Great Horned Owls, Black-crowned Night Herons, and mink have impacted this colony. 
The first chicks hatch in mid-June. Their thick natal down upperparts are cinnamon-brown to gray, brown with streaks of black, and white underparts. By mid-July the first chicks fledge, flying to and from the outer edge of the colony. After 2–4 d, the fledglings venture out over the water, unattended by their parents. There they learn fishing strategies, first by dipping down to touch the water’s surface, and even picking up floating objects. Meanwhile, their territory still serves as a family gathering place for another 10–20 days. When not experimenting with water activities, fledglings venture within and outside their territories at the colony. Since they do not actually catch fish until 20–30 days, fledglings stay on the shore or on an elevated perch and wait to be fed. The fledglings do accompany their parents to their feeding territory or even further to other fishing grounds. Families finally disperse away from the colony site. In this case (see photo) we suspect that the fledglings followed their parents from Outer Green Island to Evergreen Landing to be fed and to learn fishing skills.

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Migration
Adult females depart on migration during August, so the juveniles are apparently cared for primarily by their male parents during the staging period in late August and September. It is not known whether the male and fledglings remain together during migration and winter.

Migrating Common Terns generally fly through the night at high attitudes and rest and feed on water bodies at different times during the day. Some flocks will circle within thermals, alternating between flapping and soaring (to save energy?). Important stopover locations are located from Cape Cod to North Carolina. They may spend winter months along the southern Atlantic Coast, into the Bahamas and West Indies, and along the north and east coasts of South America including the Suriname and the Amazon River outflow system. Evidently, Common Terns take their time getting to their winter quarters. Analyses of flight dynamics showed that speeds were elevated during the northbound migration period - flight speeds and altitudes recorded were also elevated during dark hours.

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We are grateful to National Audubon’s Seabird Institute, Maine Department of Inland Fisheries and Wildlife, U.S. Fish and Wildlife Service for protecting our seabirds on Maine’s outer islands. Without their guardianship most island colonies of seabirds may have already been lost.

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By: Patty and Sam Wainright

References:
Birdsoftheworld.org
Vickery, P. “Birds of Maine”, Princeton
“Egg Rock Update Newsletter”, Seabird Institute
Dr. Don Lyons, Seabird Institute, pers. comm.
Martinkovic, M. et al. “Outer Green Island 2006 Season Report”
Caldwell, A. et al. 2025. Waterbirds, vol. 48
Allen, B. et al. 2012. Maine Atlas of Breeding Seabird and Coastal Wading Bird Colonies 1960-2011, ME Nat. Hist. Observatory

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