By: Malori Richards, DBR Field Technician
Around the beginning of May, Duxbury beach goers may have noticed a new, flashy, squawking neighbor. The new bird in town? Least terns. This tern species - the world’s smallest - cuts a striking figure on the beach. With it’s pristine white body, soft grey wings, jet black cap and eye-mask, forked tail and electric yellow bill and legs, this little bird’s breeding plumage is the demure sports car of shorebird plumages.
Least tern’s elegant breeding plumage isn’t the only noteworthy thing about these shorebirds; their behavior and sheer numbers are equally impressive. This summer they drifted onto the beach in small groups, which quickly swelled to prodigious colonies numbering in the hundreds. Least terns are colony breeders, which is why beach goers may see flocks of these birds fishing off oceanside or bayside, or gathering above their nesting sites on the sand dunes.
While they nest in colonies, least terns are monogamous, and pairs often remain together for multiple seasons. Males can often be seen presenting their mate with fresh fish, a courtship behavior that lasts throughout the breeding season. These ground-nesting birds are not known, however, for their nest-building ability. They scratch a small well, or scrape, into the sand or cobble to lay their eggs and are known to lay their eggs directly onto the ground, without any attempt at scraping. Their eggs, however, are perfectly adapted to this behavior; a creamy white or slightly olive egg speckled with browns and black, they blend in seamlessly to the cobble and sand. Females typically lay one to three eggs and the pair carefully incubates the eggs for 19-25 days before the chicks are born. Least terns are semi-precocial; meaning they hatch with their eyes open, able to walk and covered in soft yellow down feathers speckled with brown (a perfect camouflage on the beach). Nestlings stay in the nest for one to two days after their hatch-date and are fed by both parents until they leave for the winter, well after they’ve grown their feathers and learned to fly.
Least terns can be spotted bayside or oceanside off Duxbury Beach, their punctuated, swift wingbeats carrying them above the water, where they hover, spotting their preferred meal (small fish) before they strike down with stunning speed and deadly accuracy. Their fishing skills are impressive and their generosity is similarly striking - as these piscivores, or fish-eaters, often haul their catch to their mate on the beach, or in more recent weeks, to their fluffy, down-covered young. There are few things more charming than to watch a tern chick (that more resembles a fuzzy rock on little stumps than a bird) waddle as fast as it’s tiny tern legs will carry it over to an adult, who delicately offers its catch into the excited chick’s open bill. The only thing that may contend with such adorable care, is when, on rainy days, adult terns can be seen carefully brooding their fluffy young underwing.
Least terns use their large colony numbers as a method of defense against predators and, despite their size, are fiercely protective of their breeding grounds. These small birds work together to dive-bomb, squawk, (even defecate), on any potential threats that wander too close to their nests.
Despite their fierce and varied defense, this was a rough season for our least tern colonies. We lost nests and adults alike to things like overwash during some of this summer’s more severe storms, and predation by mammals and raptors. However, as anyone who has watched these birds fish or ward off intruders will know, least terns are nothing if not determined and despite major setbacks, these masked fishermen and their fluffy, wobbling young can still be found on our beach. As the summer winds down, and the chicks grow and begin to fledge, we can expect to see these birds begin their winter migration to the Carribean and South America in September. Fair warning - for those who take the time to admire these daring, determined, dashing birds, these masked shorebirds may just fly off with your heart.