Interior Least Tern Scientific Name: Sterna antillarum athalassos Federal Status: Endangered, 6/27/85 • State Status: Endangered

Description with brown mottling. Fledglings on the Arkansas, Missouri, Mississippi, Least Terns are the smallest North (young birds that have left the nest) Ohio and Platte River systems in American terns. Adults average 8 to are grayish brown and buff colored, other states. The breeding range 10 inches in length, with a 20 inch with white heads, dark bills and eye extended from Texas to Montana and wingspan. Their narrow, pointed stripes, and stubby tails. Young terns from eastern Colorado and New Mex- wings make them streamlined flyers. acquire adult plumage after their first ico to southern Indiana. It included Males and females are similar in molt at about 1 year, but do not the braided rivers of Oklahoma and appearance. Breeding adults are gray breed until they are 2 to 3 years old. southern Kansas, salt flats of north- above and white below, with a black The Least Tern’s call has been west Oklahoma, and alkali flats near cap, black nape and eye stripe, white described as a high pitched “kit,” the Pecos River in southeast forehead, yellow bill with a black or “zeep,” or “zreep.” New Mexico. brown tip, and yellow to orange legs. Today, the Interior Least Tern Hatchlings are about the size of ping- Distribution continues to breed in most of the pong balls and are yellow and buff and Habitat major river systems, but its distribu- There are three subspecies of the tion is generally restricted to the less Least Tern recognized in the United altered and more natural or little dis- States. The subspecies are identical turbed river segments. In Texas, Inte- in appearance and are segregated on rior Least Terns are found at three the basis of separate breeding ranges. The Eastern or Coastal Least Tern (Sterna antillarum antillarum), which is not federally listed as endan- gered or threatened, breeds along the Atlantic coast from Maine to Florida and west along the Gulf coast to south Texas. The California Least Tern (Sterna antillarum browni), federally listed as endan- gered since 1970, breeds along the Pacific coast from central California to southern Baja California. Breeding Range The endangered Interior Least Tern (Sterna antil- Wintering larum athalassos) breeds Range inland along the Mis- Interior Least Tern on nest souri, Mississippi, Col- © Leroy Williamson orado, Arkansas, Red, and Rio Grande reservoirs along the Rio Grande River systems. Although these sub- River, on the Canadian River in the species are generally recognized, northern Panhandle, on the Prairie recent evidence indicates that terns Dog Town Fork of the Red River in hatched on the Texas coast sometimes the eastern Panhandle, and along the breed inland. Some biologists specu- Red River (Texas/Oklahoma bound- late that the interchange between ary) into Arkansas. coastal and river populations is Nesting habitat of the Interior greater than once thought. Least Tern includes bare or sparsely The Interior Least Tern is vegetated sand, shell, and gravel migratory, breeding along inland beaches, sandbars, islands, and salt river systems in the United States flats associated with rivers and reser- and wintering along the Central voirs. The birds prefer open habitat, American coast and the northern and tend to avoid thick vegetation coast of South America from and narrow beaches. Sand and Venezuela to northeastern Brazil. gravel bars within a wide unob- Historically, the birds bred on sand- structed river channel, or open flats Least Tern and chick bars on the Canadian, Red, and Rio © TPWD Glen Mills Grande River systems in Texas, and Interior Least Tern 1 along shorelines of lakes and reser- remain in the nest for about a week. voirs, provide favorable nesting habi- As they mature, they begin to wander tat. Nesting locations are often at the from the nest, seeking shade and higher elevations away from the shelter in clumped vegetation and water’s edge, since nesting usually debris. Chicks are capable of flight starts when river levels are high and within 3 weeks, but the parents con- relatively small amounts of sand are tinue to feed them until fall migra- exposed. The size of nesting areas tion. Least Terns will renest until depends on water levels and the late July if clutches or broods are lost. extent of associated sandbars and Activities of the Interior Least beaches. Highly adapted to nesting Tern during the breeding season are in disturbed sites, terns may move limited to the portion of river near colony sites annually, depending on the nesting site. Nesting adults landscape disturbance and vegetation defend an area surrounding the growth at established colonies. nest (territory) against intruders, For feeding, Interior Least Terns and terns within a colony will need shallow water with an abun- defend any nest within that colony. dance of small fish. Shallow water When defending a territory, the incu- areas of lakes, ponds, and rivers bating bird will fly up giving an located close to nesting areas are alarm call, and then dive repeatedly Least Tern chicks preferred. at the intruder. © TPWD Glen Mills As natural nesting sites have The breeding season is usually become scarce, the birds have used complete by late August. Prior to sand and gravel pits, ash disposal migration, the terns gather at staging areas of power plants, reservoir areas with high fish concentrations. shorelines, and other manmade sites. They gather to rest and eat prior to the long flight to southern wintering Life History grounds. Low, wet sand or gravel Interior Least Terns arrive at breed- bars at the mouths of tributary streams and floodplain wetlands are ing areas from early April to early Nesting area and foraging site on the Canadian River June, and spend 3 to 5 months on important staging areas. Interior © Bruce C. Thompson the breeding grounds. Upon arrival, Least Terns often return to the same of much of the tern’s natural nesting adult terns usually spend 2 to 3 breeding site, or one nearby, year habitat in the major river systems of weeks in noisy courtship. This after year. the Midwest. Discharges from dams includes finding a mate, selecting a Nesting success of terns at a built along these river systems pose nest site, and strengthening the pair particular location varies greatly from additional problems for the birds bond. Courtship often includes the year to year. Because water levels nesting in the remaining habitat. “fish flight,” an aerial display involv- fluctuate and nesting habitats such as Before rivers were altered, summer ing aerobatics and pursuit, ending in sandbars and shorelines change over flow patterns were more predictable. a fish transfer on the ground time, the terns are susceptible to The nesting habits of the Least Tern between two displaying birds. habitat loss and frequent nest and evolved to coincide with natural Courtship behaviors also include nest chick loss. declines in river flows. Today, flow preparation and a variety of postures The Interior Least Tern is pri- regimes in many rivers differ greatly and vocalizations. marily a fish-eater, feeding in shallow from historic regimes. High flow Least Terns nest in colonies, waters of rivers, streams, and lakes. periods may now extend into the nor- where nests can be as close as 10 feet The birds are opportunistic and tend mal nesting period, thereby reducing but are often 30 feet or more apart. to select any small fish within a cer- the availability of quality nest sites The nest is a shallow depression in tain size range. Feeding behavior and forcing terns to nest in less than an open, sandy area, gravelly patch, involves hovering and diving for optimum locations. Extreme fluctua- or exposed flat. Small twigs, pieces small fish and aquatic crustaceans, tions can inundate potential nesting of wood, small stones or other debris and occasionally skimming the water areas, flood existing nests, and dry usually occur near the nest. surface for insects. out feeding areas. Egg-laying begins in late May, In portions of the range, shore- Historical flood regimes scoured with the female laying 2 to 3 eggs birds such as the Piping and Snowy areas of vegetation, providing addi- over a period of 3 to 5 days. The plovers often nest in close proximity. tional nesting habitat. However, eggs are pale to olive buff and speck- The Piping Plover is listed as Threat- diversion of river flows into reser- led or streaked with dark purplish- ened by the U.S. Fish and Wildlife voirs has resulted in encroachment of brown, chocolate, or blue-gray Service. vegetation and reduced channel width markings. Both parents incubate the along many rivers, thereby reducing eggs, with incubation lasting about Threats and Reasons sandbar habitat. Reservoirs also trap 20 to 22 days. The chicks hatch for Decline much of the sediment load, limiting within one day of each other and Channelization, irrigation, and the formation of suitable sandbar habitat. construction of reservoirs and pools In Texas and elsewhere, rivers 2 Interior Least Tern have contributed to the elimination are often the focus of recreational levels warranting concern, although (830) 775-7491, and Gene Howe reproductive difficulties have not Wildlife Management Area near been observed. Canadian in Hemphill County Finally, too little water in some (806) 323-8642 offer visitors the river channels may be a common opportunity to see and learn more problem that reduces the birds’ food about the Interior Least Tern. supply and increases access to nest- Often, the best opportunity to see ing areas by humans and predatory the birds is by boat. Please remem- mammals. Potential predators ber that human disturbance during include coyotes, gray foxes, raccoons, the nesting season reduces reproduc- domestic dogs and cats, raptors, tive success and threatens survival. American Crows, Great Egrets, and The terns should be viewed from a Great Blue Herons. distance with binoculars or spotting scope. Recovery Efforts State, federal, and private organiza- How You Can Help tions throughout the United States Interior Least Terns and other colo- are collaborating to census the birds, nial nesting shore and water birds conduct research, curtail human dis- (plovers, herons, egrets, spoonbills, Dam on the Brazos River © TPWD turbance, and provide habitat. Con- ibis, gulls, and skimmers) often nest tinued monitoring of confirmed and on sandbars and islands. These areas activities. For inland residents, sand- potential colony sites is underway to offer protection from predators, but bars are the recreational counterpart assess population status and repro- the birds are still vulnerable to of coastal beaches. Activities such as ductive success. Protective measures, human disturbance. Since the hot fishing, camping, and ATV use on and including signs and fences, are being sun can quickly kill small chicks and near sandbar habitat are potential implemented to restrict access to sites unhatched eggs if the adults are threats to nesting terns. Even sand most threatened by human distur- flushed from the nest, you can help and gravel pits, reservoirs, and other bance. Vegetation control at occupied by staying off sandbars and islands artificial nesting sites receive a high sites, chick shelter enhancement, and away from flats and shorelines level of human use. Studies have predator control, pollution abate- where birds are nesting. Also, when shown that human presence reduces ment, and habitat creation/restoration adults are flushed from the nest, the reproductive success, and human dis- at unoccupied sites are management eggs or young are more vulnerable to turbance remains a threat throughout strategies used to benefit Interior predation. Nesting areas maintained the bird’s range. Least Tern populations. as bird sanctuaries are identified by Water pollution from pesticides Biologists continue to assess official signs. If you want to observe and irrigation runoff is another habitat availability and quality the birds, bring binoculars and stay a potential threat. Pollutants entering throughout the bird’s range in Texas, safe distance away so you don’t dis- rivers upstream and within breeding and identify essential habitat for turb the birds. Pets and livestock areas can adversely affect water qual- management and protection. should also be kept off these areas ity and fish populations in tern feed- Recently, in a cooperative effort while the terns are nesting. Remem- ing areas. Least Terns are known to between the Texas Parks and Wildlife ber that state and federal laws pro- accumulate contaminants that can Department, National Park Service, tect migratory and endangered birds, affect reproduction and chick sur- International Boundary and Water and harassing them at any time is vival. Mercury, selenium, DDT deriva- Commission, Comision Internacional illegal. tives, and PCBs have been found in de Limites y Aguas, Oficina de Ecolo- You can be involved in the con- Least Terns throughout their range at gia Estado de Coahuila, and City of servation of Texas’ nongame wildlife Del Rio, warning signs in both Span- resources by supporting the Special ish and English were erected to Nongame and Endangered Species inform visitors about the effects of Conservation Fund. Special nongame human disturbance on the terns. stamps and decals are available at Also, the National Park Service Texas Parks and Wildlife Department recently initiated annual status sur- (TPWD) Field Offices, most State veys for Interior Least Terns at Amis- Parks, and the License Branch of tad NRA. Finally, public information TPWD headquarters in Austin. Con- campaigns concerning Least Tern con- servation Passports, available from servation are a vital part of the Texas Parks and Wildlife, are valid recovery process. for one year and allow unlimited access to most State Parks, State Nat- Where To See ural Areas, and Wildlife Management Interior Least Terns Areas. Some of the proceeds from Falcon State Park near Falcon Heights the sale of these items are used to in Zapata County (956) 848-5327, Banding Least Terns Amistad National Recreation Area © Bruce C. Thompson near Del Rio in Val Verde County Interior Least Tern 3 protect habitat and to provide public information concerning endangered species conservation. Conservation organizations in Texas welcome your participation and support. For More Information Contact Texas Parks and Wildlife Department Wildlife Diversity Branch 4200 Smith School Road Austin, Texas 78744 (512) 912-7011 or (800) 792-1112 or U.S. Fish and Wildlife Service Ecological Services Field Office 10711 Burnet Road, Suite 200 Bilingual “Do not Disturb” sign Austin, Texas 78758 © TPWD Sylvestre Sorola (512) 490-0057

References Hill, L.A. 1992. Status of the Least tern and Snowy plover on the Red River, 1991. Interagency Agreement No. 14-16-0002-91-923 (FWS) and G040A10001 (BLM). U.S. Bureau of Land Management, Oklahoma Resource Area, Moore, OK. 29 pp. Locknane, D.M. 1988. Interior least tern distribution and taxonomy. Texas Parks and Wildlife Dept., Federal Aid Project No. W-103-R-17, Job No. 54. 37 pp. Thompson, B.C. 1985. Interior least tern distribution and taxonomy. Texas Parks and Wildlife Dept., Federal Aid Project No. W-103-R-14, Job No. 54. 11 pp. U.S. Fish and Wildlife Service. 1990. Recovery plan for the interior population of the Least tern (Sterna antillarum). U.S. Fish and Wildlife Service, Twin Cities, Minnesota. 90 pp. Whitman, P.L. 1988. Biology and conservation of the endangered Interior least tern: a literature review. U.S. Fish and Wildlife Service, Biological Report 88(3). 22 pp.

Funds for the production of this leaflet were provided by the U.S. Fish and Wildlife Service, under Section 6 of the Endangered Species Act.

4 Interior Least Tern