Least Terns require the same open beach habitat to nest in that people seek out when they visit the shore.
Least Terns are listed as threatened by the Department of Environmental Conservation in New York state. Populations are limited by habitat availability, disturbance by beach goers and off-road vehicles, and predation due to unnaturally high predator numbers associated with human development. Although population numbers appear to have stabilized since the 1980s, the second Breeding Bird Atlas reported a 21% decline in distribution (McGowan and Corwin 2008). Without protection and management efforts for beach-nesting waterbirds, numbers in the state would likely be low.
While population numbers appear to have remained relatively stable despite high year to year variability since the 1980s, distribution has declined. Least Terns declined in distribution in New York from 87 blocks in the first atlas (1980-85) to 69 blocks in the second (2000-2005) a reduction of 21% (McGowan and Corwin 2008). One study found population numbers on Long Island increased by 49% from 1974 to 1997 but a different analysis method demonstrated a decline since 1983 (Brown et al. 2001).
Human activity has heavily influenced Least Tern population numbers, rangewide and in New York, throughout modern history. Historically, the species was common on Long Island (Giraud 1844). The Least Tern was nearly extirpated from the northeastern U.S. by hunting for feathers around the turn of the century. In New York, Least Terns were extirpated as a breeder in the state from 1882 until 1926 (Cruickshank 1942). The Lacey Act (1900) and Migratory Bird Treaty Act (1918) allowed for the species to rebound regionally in the 1920s and 30s. After this initial recovery, numbers dropped between 1950 and the early 1970s due to habitat loss, predation, and organochlorine pesticides (Kress and Hall 2004). By the mid-1970s, surveys demonstrated populations were reestablishing and around 1700 to 2600 pairs nested at 29 to 47 breeding sites (Peterson 1988b). Populations have appeared relatively stable, with year to year variability, since the 1980s with numbers ranging from around 2,000 to 3,200 pairs at 48-62 sites (McGowan and Corwin 2008, Peterson et al. 1985).
Least Terns nest on beaches and are threatened by human disturbance, increased numbers of predators associated with human development, beach driving, and vegetative succession of their limited remaining habitat. Habitat loss due to coastal development has restricted the birds to few remaining open nesting habitats that aren't inundated with people during the nesting season. Burger (1984) reported high rates of nest failure and low reproductive success among colonies in New Jersey. Nests failed due to predation by rats and crows as well as human disturbance. Nearly half of all deserted colonies (25 of 55 or 45%) failed due to human disturbance involving off-road vehicles and people walking through the colonies prior to their desertion. Remaining habitats are projected to become increasingly scarce with rising sea-levels due to global climate change and storm surges that flood nests.
Management for this species involves protecting the nesting areas and limiting disturbance to them. If nest failure rates are high and due to a few individual predators, removal including live-trapping and relocating raccoons and skunks may be necessary and effective (Burger 1989). Electric or snow fencing may be needed in areas where dogs, foxes, or raccoons pose a persistent problem (Burger 1989). Rats should be trapped and exterminated when present. Periodically reducing vegetation to keep it minimal may be needed to keep limited available habitat open in well-established colonies during periods where natural overwash of sand and scouring from flooding is not occuring. Burger (1989) reported that it was easier to remove small amounts of vegetation regularly rather than waiting until it was well-established. Posting and fencing colonies with conspicuous educational signs and limiting ORV traffic near nesting and chick foraging areas are highly beneficial (Burger 1989). Burger (1989) reported the most effective protection for Least Tern colonies was the presence of a full-time warden throughout the day for five or more days a week.
Nest productivity estimates are needed in addition to the population surveys. This will determine if colonies are successful at producing offspring to ensure long-term viability and to determine whether some colonies may be population sinks, where enough juveniles aren't being reproduced to replace the adults. If nest productivity is low causes of nest failure at specific colonies should also be identified so that action can be taken.
Least Terns nest on open sand of ocean beaches, sand flats, barrier islands and dredges. Nesting locations appear to be a tradeoff between avoiding predators that access colonies from the dunes and flooding from high tides (Burger and Gochfeld 1990). Although Least Terns select more barren and relatively homogenous habitats than other tern species, a small amount of vegetation may be useful for chicks to gain shelter once they hatch (Burger and Gochfeld 1990). Least Terns nest in colonies with other Least Terns often near Piping Plovers (Charadrius melodus); perhaps capitalizing on the increased protection from disturbance by beach goers, pets and ORVs offered by posting and fencing for Piping Plovers.
In New York, Least Terns only occur on Long Island. The first Breeding Bird Atlas documented them along the shores of Queens, Nassau, and Suffolk counties. They were absent from Staten Island and parts of Long Island Sound. The second atlas documented a shift in distribution: a range expansion on the north shore of Nassau and Suffolk counties and a reduction along Long Island's south shore bays. (McGowan and Corwin 2008)
BREEDING: Least Terns breed along the Pacific, Atlantic, and Gulf coasts and inland along large rivers. Pacific coast: central California to southern Baja California and Chiapas (Garcia and Ceballos 1995). Interior U.S.: Breeds locally along the Colorado, Red, Arkansas, Missouri, Ohio, and Mississippi river systems. The species was formerly more widespread and common but has been eliminated from much of former habitat; now breeds locally in this region, north to Montana and North Dakota, east to southwestern Indiana, central Kentucky, and western Tennessee, west to eastern Colorado. Atlantic-Gulf coast: Maine south to Florida and west to Tamaulipas, coast of Yucatan Peninsula, and in West Indies (Sprunt 1984, van Halewyn and Norton 1984); islands off coast of Belize, Honduras, and Venezuela; and Bermuda (Thompson 1995, AOU 1998). About 2/3 of world population breeds in the southeastern U.S.; largest colony is at Gulfport, Mississippi (Clapp and Buckley 1984). NONBREEDING: The nonbreeding range extends along the Pacific coast from southern Mexico to Peru and eastern coasts of Mexico, Central America, and South America to Brazil and northern Argentina (Thompson et al. 1997, AOU 1998). The species is casual in Hawaii (Whitman 1988). Birds may remain in wintering areas during first year (Thompson et al. 1995).
The Least Tern is the smallest North American tern weighing only one ounce and measuring about 9 inches in length. It is slate grey above and white below with a black cap and black extended eyeline.
The Least Tern is the smallest North American tern weighing only one ounce and 9 inches in length (21-24 cm). The sexes appear similar; breeding adults are slate gray above and white underneath. They have a black cap and nape, white forehead, black line running from the crown through the eye to the base of the bill, orange-yellow bill often with a dark tip, white or grayish underparts, short deeply forked tail, and yellow-orange legs and feet. They have a black wedge on the outer primaries is conspicuous in flight (National Geographic Society 1983). Adults in winter plumage have a dingy cap, dark nape, a black line through the eye, a dark bill, and yellowish feet and legs (National Geographic Society 1983, Peterson 1990). Juveniles are pinkish-buff above, with brownish U-shaped marks on the back, a dusky crown, and a dark bar on the front part of the folded wing. First-summer birds resemble adults but retain the dark bar on the wing and have a dark bill and dark feet and legs, dusky primaries, a dark nape, and a black line through the eye (National Geographic Society 1983, Forbush 1927, Farand 1983). Vocalizations include a male contact call "ki-dik" given when bringing fish to mate or young (Olsen and Larsson 1995), a shrill "zreep" and harsh "kip, kip, kip" alarm calls, a recognition call between pairs or adult and young when returning to the colony that is described as "k'ee-you-hud-dut" in New York (Wolk 1974), as well as a few other calls given during brooding (see Thompson et al. 1997 for further description). The eggs are pale or olive buff with dark purplish-brown or blue-gray speckles and streaks. Nests consist of shallow scrapes in the sand, soil, or pebbles and may be lined with shell fragments, small pebbles, or bits of wood or grass once incubation has begun (Wolk 1974).
The Least Tern appears similar to other tern species but is much smaller and unlike many others, the black cap stops above the eye and instead a black stripe extends across the eye to the bill. The Least Tern is also unique in that the bill and legs are an orangish- yellow instead of the reddish-orange of other similar tern species.
Adults in the breeding stage are easiest to identify although juveniles and nonbreeding adults may also be distinguised from other species.
Least Terns nest in colonies that occasionally are large but tend to be less than 25 pairs (Thompson et al 1997). They may forage singly or in small groups (Thompson et al. 1997). They are capable and acrobatic fliers with a strong direct flight. When nesting areas are threatened by a predator or intruder they respond with alarm calls and sometimes aggressive aerial dives or mobbing (Thompson et al. 1997) sometimes deficating on the intruder (Gibbons pers. comm.). Least Terns forage throughout the day. They forage by flying or hovering over waterbodies and dive, only partialy submerging, to catch fish in open mandibles (Thompson et al. 1997). They immediately resume flight and consume prey on the wing. Pairs are monogamous for the season and about half keep the same mates between seasons (Kress and Hall 2004). Both males and females tend nests and rear chicks with females spending more time at incubating and brooding chicks (Keane 1987). Chicks are altricial at hatching, meaning they have limitied mobility and thermoregulating capabilities. They are, however, covered in down and have open eyes at hatching (Thompson et al. 1997).
The diet of Least Terns consists primarily of small fish and occasional crusteaceans, although shrimp, insects, mollusks, and annelids may also be consumed (Atwood and Kelly 1984, Carreker 1985, Whitman 1988, Wilson 1991).
Least Terns may best be observed from May through August during the breeding season. They are rarely seen before May or after early September on Long Island.
The time of year you would expect to find Least Tern active and reproducing in New York.
Sternula antillarum Lesson, 1847
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This guide was authored by: Kelly A. Perkins
Information for this guide was last updated on: June 19, 2019
Please cite this page as:
New York Natural Heritage Program. 2019. Online Conservation Guide for Sternula antillarum. Available from: https://guides.nynhp.org/least-tern/. Accessed November 16, 2019.