Common Tern identification guide

The Common Tern can be fully identified by the traits shown in this photo by Brad Sylvester, copyright 2009. All rights reserved.

The Common Tern (Sterna hirundo), as the name would suggest, is the most common Tern found in New Hampshire waters by far. Steve Mirick, renowned New Hampshire birder and author of “Birding the New Hampshire Seacoast," told me that an established Tern breeding colony on Seavey and White Islands in the Isles of Shoals hosted approximately 2000-2200 pairs of Common Terns in the 2008 summer breeding season. This compares to just 5-10 pair of Arctic Terns and an even lesser number of Roseate Terns on the same islands. If you see a large group of terns, therefore, the majority of them are most likely Common Terns although Arctic and Roseate Terns will mix in with the flock in the summer range.

The Common Tern shares its distinctive black cap with other New Hampshire Terns, but has some noticeable differences that can help amateur birdwatchers tell it apart from the others. The first thing to look for is the bill. The Common Tern’s bill is reddish-orange with a black tip. The black tip will be quite noticeable, but only about 25% or less of the total length of the Common Terns’s bill.

Next, look for the upper surface of the wings when the bird is in flight. The upper wing surface of the Common Tern is light grey near the body, but will have a distinctly darker grey color toward the tip of the wings. Common Terns are graceful and agile in flight, reminding us of larger versions of the swallows that frequent fields and shorelines.

The underside of the Common Tern’s wings will show the same distinct black edging along the tip of the wing that other New Hampshire Terns will have, except that the black line along the underside of the wingtip may be a bit thicker than that of other New Hampshire Terns. The wings of the Common Tern may be just a wee bit stockier than those of the Roseate Tern, and will beat with a slower more powerful stroke than its rarer cousin.

Overall, the Common Tern will be an inch or two shorter in length than either the Roseate or Arctic Tern, though this may not be enough to make a visible difference in the field. The Common Tern measures roughly 14 inches in length as an adult.

The combination of these traits, along with the fact that it is found in the waters off the coast of New Hampshire, give a good relative certainty that the Tern in question is a Common Tern. If you don’t have a chance to get a good enough look to mark the identifying species features of a Tern you see in New Hampshire, the weight of numbers should let you start by assuming that it’s a Common Tern until you can find a specific species trait to rule out the most numerous of New Hampshire Terns. Also note that since the tern only summers in New Hampshire, this guide outlines only the summer colors and markings of the Common Tern.

I almost forgot to mention. The Common Tern will generally only be found relatively far out at sea or on small, rocky offshore islands that are used as breeding colonies. It will occasionally venture closer to shore, but rarely. If you think you see a Tern of any kind in Manchester or Keene, you are almost certainly mistaken!