Interior Least Terns are a state and federally endangered species in Nebraska. They are also considered a Tier 1 At-Risk species by the Nebraska Legacy Plan. Loss of habitat is the major reason these boisterous birds have declined in numbers. Changes to natural river flow has reduced the availability of suitable midstream sandbars with little vegetation that these birds require for nesting. These changes include such things as stream channelizaion, fluctuating flows, damming, and dredging.
Historical Accounts
Least Terns, along with Piping Plovers, are among the first birds to be described in Nebraska by western explorers. Of course, they were known by Native Americans well before that. In Nebraska, terns (and plovers) flourished along the Missouri River and its tributaries, the Platte, Loup, and Elkhorn rivers.
During the Meriwether Lewis and William Clark expedition from 1803 - 1805, Least Terns and Piping Plovers were noted in their journals in 1804. In fact, the Least Tern was described in great detail in Lewis' journals. They also took two specimens from the area near present-day Burt County for their collections.
Other historical accounts of Least Terns nesting in Nebraska include notes from the G.K. Warren expedition in the mid-1850's; 1866 in Dixon County; several accounts from Carter Lake (near Omaha) starting in 1893 until development in the early 1940's. (Ducey 1985).
Least Terns at Sand and Gravel Mines
As Nebraska became more settled and their natural nesting habitat, river sandbars, began to be modified, the birds began to look elsewhere to nest. In time, Nebraska's burgeoning sand and gravel mining industry provided the birds with prime alternative nesting habitat, sand spill piles. The first report of Least Terns nesting on sand spill piles was in unpublished field notes by Ralph E. Dawson of Lincoln, Nebraska. He first observed the terns in the summer of 1920, then again in 1922 at Capitol Beach Lake, Lincoln, Nebraska. The birds use of an alternative nesting habitat is not too surprising, because sand spill piles must look like great sandbars to the birds!
Appearance
Adult Least Terns are slightly smaller than a robin, 9 inches long from beak to tail, and 20 inches from wing tip to wing tip. They can be identified by their white body, light gray wings, yellow bill tipped with black, yellow legs, and a white forehead. In flight, the terns have slender wings and a swallow-like forked tail. They are often seen hovering over bodies of water before diving to catch small fish.
Distribution
Least Terns are divided into three subspecies, one subspecies (Sternula antillarum brownii) nests on California beaches, one subspecies (Sternula antillarum athalassos) nests on sand bars and lakeshores in the Midwest, and one subspecies (Sternula antillarum antillarum) nests on east coast beaches, and in some instances, on flat, gravelled rooftops.
In Nebraska, Least Terns were once found throughout most major river systems, but their range has been reduced because of habitat loss, most dramatically along the Missouri River and its tributaries.
Migration
Interior Least Terns migrate to Nebraska to nest. The earliest recorded arrival date is 19 April. The latest date piping plovers have been seen in Nebraska prior to their southward migration is 28 October. Several weeks prior to migration, adults and young congregate at feeding sites. Little is known about their migration to Mexico, but it is believed that the terns migrate in small family groups.
Vocalization
Sound byte Courtesy of The Macaulay Library at the Cornell Lab of Ornithology, Ithaca, New York. Recordist: Charles A. Sutherland.
Eggs and Chicks
Least Terns nest in groups, called colonies, on open sand, laying 2 - 3 eggs in a small depression in the sand. The eggs and chicks are colored and patterned like sand so they are well camouflaged. Females do 80% of the incubation of the eggs. The eggs hatch after 21 days and the chicks are able to leave the nest within hours of hatching. The chicks will be flightless and dependent on their parents for food (fish) and protection from the elements for the next 3 weeks. Terns produce only 1 successful brood each year, but may re-nest up to three times if a nest is lost early in the season. Least Tern fledglings are the size of adults, and can be distinguished by their plumage. Fledglings, or juveniles, have a dark stripe that runs through their eye, are grayish in color, and their bill is black or dark orange. It takes Least Terns three years before they begin breeding.
Defensive Behavior
The adults defend the colony by jointly mobbing any intruder and often defecating on them. If you ever have terns diving at you, defecating on you, and calling sharply, that is a clue that you are disturbing a colony and you should quickly retreat.
Life Span
Least Terns can live up to 20 years. One tern in on the East coast was documented as being 24 years old.
Disturbance
Repeated or prolonged disturbance of the birds can cause the eggs to become infertile from overheating due to excess exposure to the sun or be abandoned by the adults. Humans and human activity near nesting colonies can cause these disturbances. Humans also bring another form of disturbance - household pets and pests. Dogs, cats, and rats all have an impact on Least Tern colonies by disturbing incubating birds, destroying nests and eggs, and killing adults and chicks.
Predators pose a threat to these birds, particularly at sand and gravel mines. The natural nesting habitat of Least Terns is high, dry, sparsely-vegetated midstream sand bars. At sand and gravel mines, the areas of dry, sparsely-vegetated sand often are adjacent to areas that have many hiding places for predators, such as behind bushes and trees. Avian predators of least terns include American Kestrels (Falco sparverius), Great Blue Herons (Ardea herodias), American Crows (Corvus brachyrhynchos), and gulls. Mammalian predators include skunks, raccoons, foxes, and coyotes.
Interior Least Tern Photo/Video Gallery
Similar Species
Forster's Tern (Sterna forsteri)
Photo credit: NebraskaLAND, Nebraska Game and Parks Commission
|
Common tern (Sterna hirundo)
Photo credit: Bill Schmoker |
|
