Least Terns

Least Tern standing on the beach
A Least Tern standing in the shallow waters of the Matanzas Inlet in St. Augustine, Florida.

NPS

(Sternula antillarum)

“Don’t move! I’ll be right back with lunch!” If you could translate Tern-speak, this is what you might hear in May or June at the least tern nesting colony at the southern tip of Anastasia Island at Fort Matanzas National Monument.

Each spring this smallest member of the tern family leaves its wintering grounds along the coast of Central and South America. Some fly through Mexico to California; others follow the Mississippi River, and others fly to the eastern coast of the United States for the summer nesting season.

A social bird, least terns nest in colonies of only a few nests to several hundred nests, depending on the availability of food, suitable sand (coarse and shelly), and disturbance (or lack of it). Colonial nesting is also a protection against predators such as raccoons, dogs, and house cats. Colonies usually return to the same nesting site each year. In the past few decades, due to habitat loss and crowded beaches, some least terns have begun nesting on the flat, gravel roofs of buildings!

In late March and early April the terns begin to arrive. The male least tern dives headfirst into the water to catch a small fish which he offers to a prospective mate. She will look him over and appraise his gift. If she accepts the fish, they will become a mated pair for that season.

Here at Matanzas, there is plenty of food in the ocean and estuary, and the coarse coquina sand at the south end of Anastasia Island is ideal for least tern nests. The nest is only a shallow scraping in the sand. After mating, the female lays 2-3 cream-colored, speckled eggs which are nearly invisible against the varicolored sand. Both male and female take their turns incubating the eggs and protecting them and then the chicks from the sun.

After about 21 days, the eggs hatch into tiny, cream-colored, speckled chicks, which, for the first few days stay still in the nest, avoiding predators. After about four days the chicks are able to leave the nest and exercise their legs. Somehow, even though there might be hundreds of identical-looking chicks scurrying around the nesting grounds, the adults always know which ones are theirs (and vice versa) as the hungry chicks come running up for a meal every hour.

Within another four weeks (June and July) the young birds are fully fledged and ready to fly. However, if storms or predators wipe out the early nests, the pairs will often re-nest, extending the season into August or September.

Both parents are very protective of the nests and chicks, dive bombing and even defecating on people or animals who come near. Disturbance of the birds threatens the survival of the eggs and chicks, because when the adults are forced to fly up in defense, it leaves the eggs and chicks exposed to the hot sun and to predators such as crows, herons, and gulls. If adults are disturbed repeatedly, they may even abandon their nests.

By 1900, the species had been nearly wiped out by plume hunters seeking to satisfy the latest fashion statement-- feathers or even whole birds on women’s hats. The species never fully recovered. Least terns are now listed as a threatened species in Florida based on this previous population decline and more recently, threats to their coastal habit.

If you walk down the beach to look at the terns, please respect closed areas and keep your distance. If the birds fly up, you are too close. Leave your dog at home or keep it on a 6-foot leash. Birds perceive dogs as predators and will be disturbed even if the dog is not actively chasing them. An agitated bird is not able to look for food for its chicks. If you live close to the beach, keep your cats indoors.

Only through protection of existing breeding areas can the continued existence of least terns be assured in Florida.

The birds use only a small area of the beach for only about three months. People can have it for the rest of the year. Give terns a chance.

Last updated: August 9, 2021

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