CAPE COD’S FINEST: DO YOU KNOW TERNS? (8/03/01)

What are Cape Cod’s biggest attractions? Beautiful beaches, the Old King’s Highway, antique stops, fantastic food, whale and seal watching to name a few. However, birds should also be counted among these.

Not only is the Cape flush with cardinals, towhees, mockingbirds, catbirds, goldfinches and woodpeckers, its birds of the shore entice many a visitor here. Shorebirds by the hundreds of thousands, returning from their Arctic breeding grounds, stop along Cape shores for many weeks as they fatten up for the rest of their long journeys south. I’ll talk more about these transients in my next column.

This time, though, I want to discuss two types of highly visible birds that are an intricate part of the Cape’s beach scenes. I expect that almost every one of you knows gulls, but do you know their superficially similar cousins, the ones that are only here in the spring and summer, that fly up to 25,000 miles a year between their summer and winter homes, live on a diet exclusively of fish, nest in dense colonies, emit earnest cries that form the background for any day at a Massachusetts beach, are the symbol for the Massachusetts Audubon Society?

I’m talking terns here. Least terns. Common terns. Roseate terns. Arctic terns. Because of their similar coloring of gray, black and white, terns are either confused with gulls or overlooked by most residents and visitors who don’t make a practice of studying these ubiquitous denizens of the shore. Nonetheless, they are actually quite different in looks, behavior, food preferences and other habits. And, they are quite worth knowing.

Gulls are generally much larger than terns, and their behavior is also quite different. Gulls pose picturesquely on roof ridges. (You’ll never see a tern standing anywhere except on sand.) Gulls are fairly confident around people, eager to accept a handout of a sandwich crust or any other picnic leftover. (Terns only notice people when they enter their nesting territory and then they regard them as predators. There is nothing quite as intimidating as a tern dive bombing your head!) Gulls are large enough so that you don’t need binoculars to see them well, whereas terns take a bit of close-up study. Both species nest in colonies on beaches.

Gulls are omnivores. A sea clam or a baby tern or piping plover chick pleases them as much as a piece of pizza retrieved from a dumpster or a dead fish washed up on the beach. They are opportunistic, devouring anything that comes their way. Whatever they eat they pick up from the ground or shallow water. Terns, on the other hand, plunge-dive into the water after their prey, eating predominately sand lances (sand eels), slim, elongated marine fish that are usually silver and especially abundant in northern seas, where they live in schools below the surf.

On a recent walk on South Beach, Chatham, I watched tern after tern coming from the open ocean, a sand lance protruding from both sides of every beak, probably heading for Monomoy where they would feed this staple to their nestlings.

So, how else do you tell a tern from a gull? Terns have slim silvery bodies, long pointed wings and deeply forked tails. They fly more gracefully than the larger-bodied and more lumbering gulls. Terns’ bills are longer and more slender than gulls’ and most of those breeding in our area have bright red or orange bills.

Least terns, as the name implies, are the smallest of our terns at around 9” in length (an inch shorter than a robin). Their bills are orange-yellow with a dark tip. This tern is fairly easy to identify because of its size and bill color.

The next three species are quite similar, and it takes a good deal of time spent with a field guide to distinguish one species from another, either by its voice or its body characteristics. Common terns are 5 1/2” larger than the least with a red bill that has a dark tip. As indicated by their name, they are the most numerous of this family in this part of the East, once numbering in the hundreds of thousands of pairs. Today, however, their population has dwindled to around 10,000 pairs, declining first in the late 19th century because of plume hunters and more recently as a result of the immense expansion of gull populations.

Arctic terns, 15 1/2”, have a deep red bill. Massachusetts is the southernmost part of their breeding range, since they are truly Arctic birds. They have a precarious foothold in our area, declining from an estimated 400 pairs in the mid-40s to only a few dozen now. Roseate terns on Cape Cod, in contrast, are close to the northern extremity of their range, with a local population of under 2000 pairs.

It’s not nearly as important to recognize individual tern species as it is to learn to distinguish them from gulls and to appreciate their uniqueness. I hope the next time you are at the beach, especially where there are islands nearby offshore, such as Monomoy off Chatham, Penikese Island in Buzzards Bay and Muskeget Island off Nantucket, you will watch for these interesting avian aristocrats. I think you will come to appreciate them as I do and will want to do what you can to protect them.