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Nature Notes: Roseate Tern

Ed Robinson
May 20, 2017

Several years ago I was introduced to springtime striped bass fishing by a friend with a boat in Duxbury Bay, Massachusetts.  At first light on a bracing May morning, Dale motored slowly around the bay and used high-powered binoculars to scan the water on all sides.  In a few minutes Dale spotted a flock of small birds diving into the water, and we were soon catching large fish as fast as we could cast and release them.  The little birds around us were terns, and they swirled above the school of stripers because the stripers were pushing small bait fish to the surface, as the bait fish were frantic in their attempts to escape the marauding stripers below.  The bait fish were easy prey for the terns, who gorged their bellies to the point where they could hardly fly.  We laughed to see them resting on the surface, a satiated look on their faces.

Among the common terns and some Arctic terns were a few light colored birds we identified as roseate terns.  You had to have a quick eye to distinguish among the terns since they were in constant motion — soaring, arcing and diving into the water to emerge with fish drooping from their long bills.  It was also hard to hear the differences in their calls, since we were soon joined by a flock of raucous gulls keen to join the feeding frenzy.  With a sharp southern wind off the ocean, it made for a noisy but exciting morning on the water.

The graceful roseate tern (Sterna dougallii) is 12-15 inches long at maturity, with a wing span up to 30 inches.  With pointed wings and a long, forked tail, they are small of body, allowing them to take advantage of the lightest breezes to save energy.  The roseate has shorter wings than its cousins, and is missing a black edge on the underside of their wings.  Like other terns, they have a black top of the head and back of the neck, light gray upper wings and lustrous white feathers on their tails and underside and orange feet and legs.  The distinguishing features of the roseate tern, and the source of their name, are a small red spot that develops on their black bill and chest feathers that take on a rosy hue, both during mating season.

You can find this lovely bird in marine and tropical locations in the Northern hemisphere, with populations scattered in places like Japan, Africa and Ireland.  The subspecies we see in Maine breeds from Quebec to Long Island and they winter in South America.  The birds nest only in marine environments, including islands, beaches and salt marshes.  Ideal nesting sites are close to areas where the terns can fish for favored species such as sand lance, hake, pollock and herring.  Terns have also been observed eating crustaceans, mollusks and insects.  Once breeding colonies are established, the roseate tern tends to return to the same nesting location year after year, unless conditions deteriorate.

The roseate tern mates with only one partner in a season, but they may take a new partner the following year.  Courtship can last up to three weeks, with the male strutting with raised tail and extended neck, offering fish to his desired female.  Then the female lays two to four eggs in mid-May to mid-June, using a simple hollow in vegetation or under rocks or driftwood.  Both parents are involved in incubation of the eggs, which hatch in just over three weeks.  The parents feed the chicks until they begin to fly after three to four weeks.  Roseate terns fly in large flocks looking for food and favor shallow waters where their prey is easier to spot.  The oldest known roseate tern was a banded bird that reached 25 years.

Unfortunately the roseate tern is suffering significant population decline in most of its habitat.  It is now listed as endangered in Maine, Canada and across the US.  A number of factors have contributed to the decline, including habitat loss, disturbance of nesting sites by humans, food shortages, weather and predation by gulls and other animals.  Gulls tend to arrive in prime nesting spots before the terns, and they are known to prey upon tern eggs, chicks and adults, as are eagles, snakes and rats.  Vacation homes and campsites on prime islands have pushed the terns to more marginal sites.  The decline in fish populations has a direct effect on birds like the roseate tern and puffins, and adverse weather can affect nesting success.

Historically, roseate terns were hunted for their lovely feathers, mostly to decorate ladies’ hats.  It is estimated that the Northeast population fell as low as 2,000 breeding pairs by the late 1800’s. Fortunately the federal migratory bird legislation gave the terns a chance to recover some of their historic numbers, but other factors have become more problematic.  For example, a 1987 survey identified only 52 pairs in Maine.  Of more than 3,000 islands along Maine’s coastline, only four to six islands have been used by roseate terns in recent years.  Harpswell has 30 islands considered important for bird nesting sites, and one of them, Jenny Island, has hosted roseates in some years.

Federal and state agencies, along with conservation groups such as Maine Audubon, have rallied to try and help the roseate terns, along with other threatened coastal birds.  Ten Maine islands are managed specifically for tern habitat, with steps taken to remove gulls, control human disturbance and use decoys and recordings to attract nesting terns.  These steps resulted in 289 pairs of roseates being recorded in 2001.  In Harpswell, 30 islands are considered important seabird nesting sites, and are zoned for resource protection, with visitors not allowed between March 15 and August 15.  The Maine Department of Inland Fisheries and Wildlife monitors all projects funded and carried out by municipalities and state agencies in areas within a quarter mile of known roseate tern nesting sites.

It would be wonderful to think that the roseate tern can recover some of its numbers with an assist from us.  In Ireland, there are reports of success using nesting boxes to give the roseate tern eggs more protection from predators.  Boaters can help by avoiding known nesting islands, and efforts are underway to keep pets under control along important beaches.  Offshore aquaculture sites are kept away from nesting islands and fisherman are encouraged to keep gill nets away from known feeding areas.  The work of HHLT to protect and conserve Harpswell’s islands, such as Little Yarmouth Island, is an important part of this long-term effort.

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