Description
The interior least tern is a feisty, swallow-like bird eight to nine inches long
with a wing span of 20 inches. It was once called sea swallow for its
delicate, graceful and buoyant flight. In breeding plumage, it is
distinguishable from other terns
 by
its glossy black crown, white forehead and undersurface, pale gray back and
wings, and the black-tipped yellow-orange bill.
The short legs and webbed feet of the male are orange, those of the female pale
yellow. The long, black outermost wing feathers and the short, deeply forked
tail are conspicuous in flight. The plumage of immature terns is darker gray
than the adults. Immature birds have a dark bill, a dark gray eye stripe, a
white forehead and a dusky brown cap.  Young
birds acquire adult plumage characteristics during their second year. Wintering
birds are paler than breeding birds and are identifiable by their brownish-black
bill, dark gray eye stripe and white and black feathers on the head. The orange
legs and feet become a pale yellow.
Food
Interior least terns consume small fish captured in the shallow water of rivers
and lakes. They hunt by hovering, searching and then diving from a height of a
few feet to 30 feet above the surface to snatch small fish in their bill.
 The
most common fish species taken in Nebraska include several shiner species (Notropis
sp.) and plains killifish (Fundulus kansae), but they will eat almost any fish
species of appropriate size.
Least terns nesting at sandpits and other off-river sites often fly up to two
miles to forage at river sites. Least terns nesting on riverine sandbars usually
forage close to the nesting colony. Fish of one to three inches long are
consumed by adults. Young chicks are consistently brought nonspiny fish within
the size range of one-half to two inches long. Adults and young birds swallow
the fish whole, head first and usually in one gulp.
Status
The least tern, the smallest member of the tern family, is represented by three
distinct subspecies. The coastal least tern (Sterna a. antillarum)
breeds along the U.S. coast from the southern tip of Texas north to southern
Maine; the California least tern (Sterna a. brownii) breeds from southern Baja
California and Mexico, north to San Francisco Bay; the interior least tern
(Sterna a. athalassos) breeds locally along the major tributaries of the
Mississippi River drainage basin from eastern Montana south to Texas and east to
western Illinois, Missouri, Arkansas and Louisiana.
All subspecies of the least tern apparently were abundant through the late
1880s, but were nearly extirpated as changing fashions popularized bird feathers
and skins on hats.  In
the late 1800s it was reported that as many as 1,200 adult least terns were
killed for their delicate plumage in one day, and as many as 100,000 were killed
in one season.
After the signing of the 1918 Migratory Bird Treaty Act, which prohibited the
sale, purchase, taking or possession of any wild migratory bird, commercial
harvesting became illegal and the species began to increase through the 1940s.
However, human development and use of tern nesting beaches for housing and
recreation subsequently lead to another rapid population decline. In the
interior United States, river channelization, irrigation diversions and the
construction of dams contributed to the destruction of much of the terns’
sandbar nesting habitat. By the mid-1970s, least tern populations had decreased
by more than 80 percent from the 1940s.
State and federal wildlife agencies, along with a concerned public, believed
protective measures were appropriate. The California and interior populations of
the least tern were federally listed as endangered in 1970 and 1985,
respectively. The coastal least tern (more than 75 percent of the total least
tern population) was not federally listed, but is protected by state laws as a
threatened or endangered species.
The first historical observation of the least tern in Nebraska was recorded
along the Missouri River by the Lewis and Clark expedition of 1804. Notes of
Lewis and Clark refer to the least tern as a frequently observed bird. In
addition to the Missouri River, the historic breeding range of the least tern in
Nebraska included the Platte River from its mouth west to the confluence of the
North and South Platte rivers, including reaches of the North and South Platte
rivers, the Loup River and about 100 miles of the lower Niobrara River.
Beginning in the 1930s, the wide braided channels of the Missouri River were
slowly narrowed to a single navigation channel. Between Sioux City, Iowa, and
St. Louis, Missouri, almost all Missouri River sandbar nesting habitat was lost.
Records show that from 1890 to 1976, sandbar habitat was reduced from 35,273
acres to 57 acres along the Iowa-Nebraska border. Along the Platte River system,
reservoirs and irrigation diversions have severely reduced river flows and
curtailed the scouring effects of ice and spring floods. Those reductions
accelerated the encroachment of vegetation onto river sandbars, an effect most
pronounced in the central and upper Platte River reaches. Diversion of water
along the Loup River also limits least tern nesting distribution.
The extraction of sand and gravel for commercial use is another change that
occurred as rivers were developed. Sand and gravel mines created open sandpit
lakes and bare sandpiles on the river floodplain. As riverine nesting habitat
became increasingly limited, least terns began to nest on the bare spoil piles
at sandpits. The current breeding distribution of the interior least tern is now
restricted to localized sites and river reaches throughout its historic range.
In Nebraska, least terns currently breed along the Platte River from its mouth,
west to North Platte, at one or two isolated sites along the South Platte, along
the lower reaches of the Niobrara River, along reaches of the Loup and Elkhorn
rivers and on the unchannelized section of the Missouri River below the Fort
Randall and Gavins Point dams. A few least terns nest on the shoreline of Lake
McConaughy on the North Platte River, usually in years when low lake levels
expose wide, sandy beaches.
The total population of interior least terns has been estimated at 4,700 to
5,000 adults. Recent population information for least terns in Nebraska,
including stretches of the Missouri River shared with South Dakota, suggests a
total of 1,200 to 1,400 birds. If the interior least tern is to be down-listed
from endangered to threatened status, the total interior population will have to
increase to 7,000 adults, including 1,520 adults in Nebraska. Those population
levels will have to remain stable for at least 10 years, and critical habitat
will have to be secured and maintained. |
