Bird of the Month: Common Tern
Written by Andy McCormick
Andy McCormick, Volunteer and Former Board President of Eastside Audubon
Remembering the recovery of the Common Tern is fitting as we celebrate the 100th anniversary of the Migratory Bird Treaty Act of 1918.
Common Tern
Scientific Name: Sterna hirundo
Length: 12”
Wingspan: 30”
Weight: 4.2 oz (120 g)
AOU Alpha Code: COTE
BACK FROM NEAR EXTIRPATION
Hunted in the extreme in the late 19th Century, the Common Tern was almost completely absent from the Atlantic Coast by the 1880s. Millions of these exquisite birds were killed for their feathers for the millinery trade. Sometimes whole stuffed terns were used to decorate women’s hats. The slaughter of these birds, as well as herons and other birds, led to the founding of the National Audubon Society and the signing of the Migratory Bird Treaty Act. The Common Tern recovered quickly and by the 1930s was populating its previous range again (Nisbet, et al).
Similar to Forster’s and Arctic Tern, the breeding Common Tern is grey with a black cap, red legs, and red bill with black tip. It can be distinguished from other similar size terns by the dark carpal bar across the front of the wing in flight, and at the top of the wing when perched. They also show a dark wedge in the outer primaries in flight (Alderfer). The Common Tern is in the large genus Sterna, originally from the Old English stern or starn, a tern. Its species name hirundo is Latin for swallow. An old common name for terms was sea swallows (Holloway). You can see videos of Common Terns flying and feeding at Macaulay Library
INLAND COLONIAL NESTER
Common Terns breed at inland sites in Canada from the Northwest Territories and Alberta to the Atlantic Provinces and in the United States in northern Montana and around the Great Lakes and at some sites in the east. Research data from the recovery of banded Common Terns indicates that those which breed in Alberta and Saskatchewan are those most likely to be seen in Washington during spring and fall migrations. These birds move along the Pacific Flyway and winter on the Pacific coast from Mexico to Costa Rica (Nisbet, et al).
Common Terns usually begin breeding at 3-4 years of age. They nest in colonies often on islands or promontories around barrier beaches and salt marshes. The nest is a scrape on bare ground. Usually, 1-3 buff to pale blue or olive eggs are deposited. Both parents incubate for about three weeks and then feed hatchlings until they make their first flight. Juvenile terns can remain with the parents for another two months or more.
NEEDS A LITTLE HELP FROM HUMAN FRIENDS
Although Common Tern numbers have improved since the last quarter of the 20th Century, they are still far below historical levels. They have been displaced from many of their traditional breeding sites by large predatory gulls such as Herring and Greater Black-backed Gulls in the east, and Ring-billed Gulls in the Great Lakes area.
Significant management interventions on their behalf have included creation of artificial sites such as islands composed of dredged material in the St. Lawrence River, and construction of piers and floating structures. At a site in North Carolina seawalls have been built higher to protect the birds from higher sea level and storm surges. Site managers often play recordings of Common Tern calls to attract them to speed up the repopulation of breeding areas
CONTINUING THREATS AND NEEDS
Due to the nature of the threats against Common Terns: Displacement by gulls, rising sea levels due to climate change, disturbance by human recreational activities around waterways, and a high rate of susceptibility to toxic chemicals, continued management by humans will be necessary into the future. Today, 60% of Common Tern breeding areas are on managed sites.
Photo credit Mick Thompson.
References available upon request from amccormick@eastsideaudubon.org.