Thursday, July 13, 2017

Interior Least Terns

If you have visited Hagerman National Wildlife Refuge in the last week you have probably noticed that C Pad and D Pad are barricaded. These pads are sites that the Least Terns have chosen to build their nests. The Interior Least Tern is an endangered species due to loss of habitat and is protected by Federal Regulations.

According to Paul Balkenbush, HNWR Deputy Manager, on July 5, 2017, "We observed about 24 adults foraging and loafing including 16 on C Pad and 8 on D Pad. There was some transfer between pads so a total count was challenging. We also observed three ILT nests (one on C Pad and two on D Pad) but there could have been more. We did not venture close enough to be certain because of the potential of stepping on eggs. Both C and D pads are protected from traffic via barricades. I plan to take another look tomorrow to see if there is ILT activity on other pads that need to be protected."

Nesting Tern, 2011, by Jack Chiles
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 forehead and an orange-yellow bill with a dark tip. The underparts 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.

The terns are late this year. 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.

Where's Waldo?  Find the Tern chick in this photo, taken in 2009 by Dick Malnory
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.
Tern parent with chick, 2011, by Eileen Sullivan
In an effort to help the terns successfully raise 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. 

For 2017, two artificial "Tern Islands" have been placed in the lake near the pads off Oilfield Roads, but so far they have not accepted them for nesting places.  Balkenbush says"No terns were observed on the nesting platforms or showing any interest in them. I am concerned that the newly-added cross wires (to deter predators) might be making the artificial habitat less desirable. I am considering removing the cross wires from at least one platform tomorrow to see if it makes a difference. We will also put out some decoys on both. Seems like a good opportunity for an experiment."

Tern Island I, 2015
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.

Interior Least Tern in Flight, 2011, by Laurie Sheppard
Text by Jack Chiles, Texas Master Naturalist, originally published on July 13,  2011, updated for July, 2017 by the editor.

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