Nesting Least Terns at Hagerman NWR

If you have visited Hagerman NWR in the last few weeks you have probably noticed that several of the pads (Tern Pad, “D” Pad, and “F” Pad at present) are barricaded. These pads are sites that the Least Terns have chosen to build their nests. The Interior Least Tern is an endangered species and is protected in Texas by Federal Regulations.

The Least Tern is the smallest of the North American terns. The breeding adult is gray above, with a black head and nape and with black extending from the eye to the bill. It has a white fore-head and an orange-yellow bill with a dark tip. The under parts are white and the legs orange-yellow. In flight look for the black wedge on the outer primaries (the outermost wing feathers) and the short deeply forked tail. An average adult is 8 to 10 inches in length and has a 20 inch wingspan.

Interior Least Terns usually begin nesting here in late May or early June preceded by 2 to 3 weeks of noisy courtship. This includes finding a mate, selecting a nest site, and strengthening the pair bond. Courtship often includes the “fish flight”, an aerial display involving aerobatics and pursuit, ending in a fish transfer on the ground between two displaying birds. Courtship behaviors also include nest preparation and a variety of postures and vocalizations. Least Terns are colony nesters where nests can be as close as 10 feet apart but often are more than 30 feet apart. The nest that you usually see here is a very shallow depression in the gravel.

Egg-laying usually begins in late May with the female laying 2 to 3 eggs over a period of 3 to 5 days which are then incubated with the male and female alternately sharing duties for a period of about 21 days. The eggs are pale to olive buff and speckled or streaked with dark purplish-brown, chocolate or blue-gray markings.

Nesting adults defend an area surrounding the nest (territory) against intruders. Intruders can include humans, coyotes, fox, raccoons, bobcats, domestic dogs and cats, American Crows, Great Egrets, and Great Blue Herons among other creatures. When defending a territory, the incubating bird will fly around giving an alarm call and diving repeatedly at the intruder.

The chicks hatch within one day of each other and remain in the nest for about a week. Then they will wander from the nest in search of shade or cover. They will be able to fly within 3 weeks of hatching.

For feeding the Least Terns need shallow water like we have at Hagerman NWR which provides an abundance of small fish.

In an effort to help the terns be successful in raising their young we monitor the terns a minimum of once a week during the nesting season. We try to locate all the nests and map them out. Then we keep records of eggs laid, eggs successfully hatched and birds that fledge. We have cameras at each colony monitoring for problems such as varmints enabling us to possibly head off future problems. We put out logs and driftwood for shade.

The Least Terns will probably be observed around the pads until late August. After the Least Terns leave in late summer we will be anxiously awaiting their return next spring as they usually return to the same breeding site year after year.

Text and photo by Jack Chiles.

For more information about Hagerman National Wildlife Refuge,the official website is http://www.fws.gov/southwest/refuges/texas/hagerman/index.html

For information about the Friends of Hagerman, see http://www.friendsofhagerman.com.