Least tern

Last updated

Least tern
Least Tern (Sternula antillarum) RWD1.jpg
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Class: Aves
Order: Charadriiformes
Family: Laridae
Genus: Sternula
Species:
S. antillarum
Binomial name
Sternula antillarum
Lesson, 1847
Sternula antillarum map.svg
Synonyms

Sterna antillarum

The least tern (Sternula antillarum) is a species of tern that breeds in North America and locally in northern South America. It is closely related to, and was formerly often considered conspecific with, the little tern of the Old World. Other close relatives include the yellow-billed tern and Peruvian tern, both from South America.

Contents

It is a small tern, 22–24 cm (8.7–9.4 in) long, with a wingspan of 50 cm (20 in), and weighing 39–52 g (1.4–1.8 oz). The upper parts are a fairly uniform pale gray, and the underparts white. The head is white, with a black cap and line through the eye to the base of the bill, and a small white forehead patch above the bill; in winter, the white forehead is more extensive, with a smaller and less sharply defined black cap. The bill is yellow with a small black tip in summer, all blackish in winter. The legs are yellowish. The wings are mostly pale gray, but with conspicuous black markings on their outermost primaries. It flies over water with fast, jerky wingbeats and a distinctive hunchback appearance, with the bill pointing slightly downward.

It is migratory, wintering in Central America, the Caribbean and northern South America. Many spend their whole first year in their wintering area. [2] It has occurred as a vagrant to Europe, with one record in Great Britain and one in Ireland.

It differs from the little tern mainly in that its rump and tail are gray, not white, and it has a different, more squeaking call; from the yellow-billed tern in being paler gray above and having a black tip to the bill; and from the Peruvian tern in being paler gray above and white (not pale gray) below and having a shorter black tip to the bill.

Subspecies

The differences among the three subspecies may not be as much as had been thought. [3] [4]

Parent feeding a small chick in Florida, USA Sternula antillarum -St Augustine, Florida, USA -parent and chick-8.jpg
Parent feeding a small chick in Florida, USA

Additionally, least terns of an unknown subspecies were found in 2012 nesting on the Big Island of Hawaii. [5]

Conservation and status

S. a. antillarum

The population is about 21,500 pairs; it is not currently considered federally threatened, though it is considered threatened in many of the states in which it breeds. Threats include egg and fledgling predators, high tides and recreational use of nesting beaches.

S. a. athalassos

The interior subspecies, with a current population of about 7000 pairs, was listed as an endangered subspecies in 1985 (estimated 1000 breeding pairs), due to loss of habitat caused by dams, reservoirs, channelization, and other changes to river systems. It was delisted on 13 January 2021. [6]

S. a. browni

The western population, the California least tern, was listed as an endangered species in 1972 with a population of about 600 pairs. With aggressive management, mainly by the exclusion of humans via fencing, the Californian population has rebounded in recent years to about 4500 pairs, a marked increase from 582 pairs in 1974 when census work began, though it is still listed as an endangered subspecies. [3] [4] The California subspecies breeds on beaches and bays of the Pacific Ocean within a very limited range of southern California, in San Francisco Bay and in northwestern Mexico. While numbers have gradually increased with its protected status, it is still vulnerable to predators, natural disasters or further disturbance by humans. Recent threats include the gull-billed tern (Sterna nilotica), which can decrease reproductive success in a colony to less than 10%. [7]

Nesting and breeding behavior

The least tern arrives at its breeding grounds in late April. The breeding colonies are not dense and may appear along either marine or estuarine shores, or on sandbar islands in large rivers, or in areas free from humans or predators. Courtship typically takes place removed from the nesting colony site, usually on an exposed tidal flat or beach. Only after courtship has confirmed mate selection does nesting begin by mid-May and is usually complete by mid-June. Courtship takes the form of either an aerial display in which the female follows the flight of the male or through courtship feeding. [8] Nests are situated on barren to sparsely vegetated places near water, normally on sandy or gravelly substrates. In the southeastern United States, many breeding sites are on white gravel rooftops. [9] In the San Francisco Bay region, breeding typically takes place on abandoned salt flats. Where the surface is hard, this species may use an artificial indentation (such as a deep dried footprint) to form the nest basin.

The nest density may be as low as several per acre, but in San Diego County, densities of 200 nests per acre have been observed. Most commonly the clutch size is two or three, but it is not rare to consist of either one or four eggs. Adults are known to wet themselves and shake off the water over the eggs when arriving at the nest. [10] Both females and males incubate the eggs for a period of about three weeks, and both parents tend the semiprecocial young. Young birds can fly at age four weeks. After the formation of the new families, groupings of birds may appear at lacustrine settings in proximity to the coast. Late-season nesting may be renests or the result of late arrivals. In any case, the bulk of the population has left the breeding grounds by the end of August.

Feeding and roosting characteristics

The least tern hunts primarily in shallow estuaries and lagoons, where smaller fishes are abundant. It hovers until spotting prey, and then plunges into the water without full submersion to extract meal. The most common prey recently for both chicks and adults are silversides smelt ( Atherinops spp.) and anchovy ( Anchoa spp.) in southern California, [11] as well as shiner perch, and small crustaceans elsewhere. Adults in southern California eat kelpfish (most likely giant kelpfish, Heterostichus rostratus). [11] Insects are known to be eaten during El Niño events. [12] [13] In southern California, least terns feed in bays and lagoons, near shore, and more than 24 km (15 mi) from shore in the open ocean. [11] Elsewhere, they feed in proximity to lagoons or bay mouths.

Adults do not require cover, so that they commonly roost and nest on the open ground. After young chicks are three days old, they are brooded less frequently by parents and require wind blocks and shade, and protection from predators. In some colonies in southern California, Spanish roof tiles are placed in colonies so chicks can hide there. Notable disruption of colonies can occur from predation by burrowing owls, gull-billed terns and American kestrels. [14] Depredation by domestic cats has been observed in at least one colony. [15] Predation on inland breeding terns by coyotes, bobcats, feral dogs and cats, great blue herons, Mississippi kites, and owls has also been documented. [3] [4] [16]

Related Research Articles

<span class="mw-page-title-main">Black-necked grebe</span> Water bird from parts of Africa, Eurasia, and the Americas.

The black-necked grebe or eared grebe is a member of the grebe family of water birds. It was described in 1831 by Christian Ludwig Brehm. There are currently three accepted subspecies, including the nominate subspecies. Its breeding plumage features a distinctive ochre-coloured plumage which extends behind its eye and over its ear coverts. The rest of the upper parts, including the head, neck, and breast, are coloured black to blackish brown. The flanks are tawny rufous to maroon-chestnut, and the abdomen is white. When in its non-breeding plumage, this bird has greyish-black upper parts, including the top of the head and a vertical stripe on the back of the neck. The flanks are also greyish-black. The rest of the body is a white or whitish colour. The juvenile has more brown in its darker areas. The subspecies californicus can be distinguished from the nominate by the former's usually longer bill. The other subspecies, P. n. gurneyi, can be differentiated by its greyer head and upper parts and by its smaller size. P. n. gurneyi can also be told apart by its lack of a non-breeding plumage. This species is present in parts of Africa, Eurasia, and the Americas.

<span class="mw-page-title-main">Tern</span> Family of seabirds

Terns are seabirds in the family Laridae that have a worldwide distribution and are normally found near the sea, rivers, or wetlands. Terns are treated as a subgroup of the family Laridae which includes gulls and skimmers and consists of eleven genera. They are slender, lightly built birds with long, forked tails, narrow wings, long bills, and relatively short legs. Most species are pale grey above and white below, with a contrasting black cap to the head, but the marsh terns, the Inca tern, and some noddies have dark plumage for at least part of the year. The sexes are identical in appearance, but young birds are readily distinguishable from adults. Terns have a non-breeding plumage, which usually involves a white forehead and much-reduced black cap.

<span class="mw-page-title-main">Common tern</span> Migratory seabird in the family Laridae with circumpolar distribution

The common tern is a seabird in the family Laridae. This bird has a circumpolar distribution, its four subspecies breeding in temperate and subarctic regions of Europe, Asia and North America. It is strongly migratory, wintering in coastal tropical and subtropical regions. Breeding adults have light grey upperparts, white to very light grey underparts, a black cap, orange-red legs, and a narrow pointed bill. Depending on the subspecies, the bill may be mostly red with a black tip or all black. There are several similar species, including the partly sympatric Arctic tern, which can be separated on plumage details, leg and bill colour, or vocalisations.

<span class="mw-page-title-main">Yellow-crowned night heron</span> Species of bird

The yellow-crowned night heron, is one of two species of night heron in genus Nyctanassa. Unlike the black-crowned night heron, which has a worldwide distribution, the yellow-crowned is restricted to the Americas. It is known as the bihoreau violacé in French and the pedrete corona clara in Spanish.

<span class="mw-page-title-main">Little tern</span> Species of bird

The little tern is a seabird of the family Laridae. It was formerly placed into the genus Sterna, which now is restricted to the large white terns. The genus name is a diminutive of Sterna, 'tern'. The specific albifrons is from Latin albus, 'white', and frons, 'forehead'. The former North American and Red Sea S. a. saundersi subspecies are now considered to be separate species, the least tern and Saunders's tern.

<span class="mw-page-title-main">Pigeon guillemot</span> Seabird in the auk family from North Pacific coastal waters

The pigeon guillemot is a species of bird in the auk family, Alcidae. One of three species in the genus Cepphus, it is most closely related to the spectacled guillemot. There are five subspecies of the pigeon guillemot; all subspecies, when in breeding plumage, are dark brown with a black iridescent sheen and a distinctive wing patch broken by a brown-black wedge. Its non-breeding plumage has mottled grey and black upperparts and white underparts. The long bill is black, as are the claws. The legs, feet, and inside of the mouth are red. It closely resembles the black guillemot, which is slightly smaller and lacks the dark wing wedge present in the pigeon guillemot.

<span class="mw-page-title-main">Roseate tern</span> Bird in the family Laridae

The roseate tern is a species of tern in the family Laridae. The genus name Sterna is derived from Old English "stearn", "tern", and the specific dougallii refers to Scottish physician and collector Dr Peter McDougall (1777–1814). "Roseate" refers to the bird's pink breast in breeding plumage.

<span class="mw-page-title-main">Lesser crested tern</span> Species of bird

The lesser crested tern is a tern in the family Laridae.

<span class="mw-page-title-main">Forster's tern</span> Species of bird

Forster's tern is a tern in the family Laridae. The genus name Sterna is derived from Old English "stearn", "tern", and forsteri commemorates the naturalist Johann Reinhold Forster.

<span class="mw-page-title-main">Aleutian tern</span> Species of bird

The Aleutian tern is a migratory bird living in the subarctic region of the globe most of the year. It is frequently associated with the Arctic tern, which it closely resembles. While both species have a black cap, the Aleutian tern may be distinguished by its white forehead. During breeding season, the Arctic terns have bright red bills, feet, and legs while those of the Aleutian terns are black.

<span class="mw-page-title-main">Greater crested tern</span> Seabird in the family Laridae

The greater crested tern, also called crested tern or swift tern, is a tern in the family Laridae that nests in dense colonies on coastlines and islands in the tropical and subtropical Old World. Its five subspecies breed in the area from South Africa around the Indian Ocean to the central Pacific and Australia, all populations dispersing widely from the breeding range after nesting. This large tern is closely related to the royal and lesser crested terns, but can be distinguished by its size and bill colour.

<span class="mw-page-title-main">Black-legged kittiwake</span> Species of bird

The black-legged kittiwake is a seabird species in the gull family Laridae.

<span class="mw-page-title-main">California gull</span> Species of bird

The California gull is a medium-sized gull, smaller on average than the herring gull, but larger on average than the ring-billed gull. It lives not just in California, but up and down the entire Western coast of North America, and has breeding ground inland. The yellow bill has a black ring.

<span class="mw-page-title-main">White-fronted tern</span> Species of bird

The white-fronted tern, also known as tara, sea swallow, black-billed tern, kahawai bird, southern tern, or swallow tail, was first described by Johann Friedrich Gmelin in 1789. A medium-sized tern with an all-white body including underwing and forked tail, with grey hues on the over the upper side of the wing. In breeding adults a striking black cap covers the head from forehead to nape, leaving a small white strip above the black bill.

<span class="mw-page-title-main">New Zealand fairy tern</span> Subspecies of bird

The New Zealand fairy tern or tara-iti is a subspecies of the fairy tern endemic to New Zealand. It is New Zealand's rarest native breeding bird, with about 40 individuals left in the wild. It nests at four coastal locations between Whangarei and Auckland in the North Island. It is threatened by introduced predators, extreme storms and tides, beach activity, and waterfront development.

<span class="mw-page-title-main">California least tern</span> Subspecies of bird

The California least tern, Sternula antillarum browni, is a subspecies of least tern that breeds primarily in bays of the Pacific Ocean within a very limited range of Southern California, in San Francisco Bay and in northern regions of Mexico. This migratory bird is a U.S. federally listed endangered subspecies. The total population of the subspecies amounted to 582 breeding pairs in 1974, when census work on this bird began. While numbers have gradually increased with its protected status, the species is still vulnerable to population decline through natural disasters, predation, and human disturbance.

<span class="mw-page-title-main">Fairy tern</span> Species of bird

The fairy tern is a small tern which is native to the southwestern Pacific. It is listed as "Vulnerable" by the IUCN and the New Zealand subspecies is "Critically Endangered".

<span class="mw-page-title-main">Damara tern</span> Species of bird

The Damara tern is a species of small tern in the family Laridae which breeds in the southern summer in southern Africa and migrates to tropical African coasts to winter.

<span class="mw-page-title-main">Peruvian tern</span> Species of bird

The Peruvian tern is a species of tern in the family Laridae. Found in northern Chile, Ecuador, and Peru, its natural habitats are hot deserts, sandy shores, and coastal saline lagoons. It is threatened by habitat loss.

<span class="mw-page-title-main">Seabird breeding behavior</span>

The term seabird is used for many families of birds in several orders that spend the majority of their lives at sea. Seabirds make up some, if not all, of the families in the following orders: Procellariiformes, Sphenisciformes, Pelecaniformes, and Charadriiformes. Many seabirds remain at sea for several consecutive years at a time, without ever seeing land. Breeding is the central purpose for seabirds to visit land. The breeding period is usually extremely protracted in many seabirds and may last over a year in some of the larger albatrosses; this is in stark contrast with passerine birds. Seabirds nest in single or mixed-species colonies of varying densities, mainly on offshore islands devoid of terrestrial predators. However, seabirds exhibit many unusual breeding behaviors during all stages of the reproductive cycle that are not extensively reported outside of the primary scientific literature.

References

  1. BirdLife International (2018). "Sternula antillarum". IUCN Red List of Threatened Species . 2018: e.T22694673A132567260. doi: 10.2305/IUCN.UK.2018-2.RLTS.T22694673A132567260.en . Retrieved 19 November 2021.
  2. 1 2 Thompson, Bruce C.; Jackson, Jerome A.; Burger, Joanna; Hill, Laura A.; Kirsch, Eileen M.; Atwood, Jonathan L. (1997). Poole, A. (ed.). "Least Tern (Sterna antillarum)". The Birds of North America Online. Ithaca: Cornell Lab of Ornithology. doi:10.2173/bna.290.
  3. 1 2 3 Draheim, H.; Baird, P.; Haig, S. (2012). "Temporal Analysis of mtDNA Variation Reveals Decreased Genetic Diversity in Least Terns". The Condor. 114 (1): 145–154. doi: 10.1525/cond.2012.110007 .
  4. 1 2 3 Draheim, H.; Miller, M.; Baird, P.; Haig, S. (2010). "Subspecific Status and Population Genetic Structure of Least Terns (Sternula antillarum) Inferred by Mitochondrial DNA Control-Region Sequences and Microsatellite DNA". The Auk. 127 (4): 807–819. doi:10.1525/auk.2010.09222. S2CID   14033381.
  5. Szcyzs, P.; Waddington, S.; Burr, T.; Baird, P. (2014). "Least Terns Nesting on the Big Island of Hawaii". Proceedings of the 38th Annual Meeting of the Waterbird Society. La Paz, Mexico.
  6. DEPARTMENT OF THE INTERIOR, Fish & Wildlife Service. "Endangered and Threatened Wildlife and Plants; Removal of the Interior Least Tern From the Federal List of Endangered and Threatened Wildlife" (PDF). Retrieved 22 January 2021.
  7. Marschalek, D. (2009). California Least Tern Breeding Survey 2009 Season (Report). California Department of Fish and Game.
  8. "Least Tern". Audubon. 13 November 2014. Retrieved 6 February 2021.
  9. Forys, Elizabeth A.; Borboen-Abrams, Monique (2006). "Roof-top Selection by Least Terns in Pinellas County, Florida". Waterbirds. The Waterbird Society. 29 (4): 501–506. doi:10.1675/1524-4695(2006)29[501:RSBLTI]2.0.CO;2. S2CID   84920888.
  10. Tomkins, Ivan R. (1959). "Life history notes on the least tern" (PDF). Wilson Bulletin. 71 (4): 313–322.
  11. 1 2 3 Baird, P. (2009). Foraging Study of California Least Terns in San Diego Bay and Near ocean Waters (Unpublished Report). San Diego California: United States Navy.
  12. Baird, P.; Hink, S.; Robinette, D.; Wawerchak, V. (1997). Monitoring of the Least Tern Colony during the X Games in Mission Bay Park, 1997 (Unpublished Report). ESPN and the City of San Diego.
  13. Baird, P.; Hink, S.; Robinette, D.; Wawerchak, V. (1998). Monitoring of the Least Tern Colony during the X Games in Mission Bay Park, 1998 (Unpublished Report). ESPN and the City of San Diego.
  14. Collins, L.; Bailey, S. (1980). California least tern nesting season at Alameda Naval Air Station - 1980 (Report).
  15. Zeiner, David C.; Laudenslayer, William F.; Meyer, Kenneth E., eds. (November 1988). California Wildlife. Vol. II, Birds. California Department of Fish and Game. ASIN   B0026C80G6.
  16. Jones, Ken (1997–2006). "Least tern data archives".