Antarctic tern

== Description ==

== Description ==

The Antarctic Tern is a medium-sized tern ranging from {{Convert|35 to 40|cm|in|abbr=on}} in length with a wingspan of {{Convert|74 to 79|cm|in|abbr=on}}. It weighs between {{Convert|150 and 180|g|oz|abbr=on}} but it tends to be heavier during the winter months.<ref name=”:0″>{{Cite book|last1=Gochfeld|first1=M.|title=Birds of the World|last2=Burger|first2=J.|last3=Garcia|first3=E. F. J.|publisher=Cornell Lab of Ornithology|year=2020|location=Ithaca, NY, USA|chapter=Antarctic Tern (Sterna vittata)}}</ref>

The Antarctic Tern is a medium-sized tern ranging from {{convert|35 to 40|cm|in|abbr=on}} in length with a wingspan of {{convert|74 to 79|cm|in|abbr=on}}. It weighs between {{convert|150 and 180|g|oz|abbr=on}} but it tends to be heavier during the winter months.<ref name=”:0″>{{Cite book|last1=Gochfeld|first1=M.|title=Birds of the World|last2=Burger|first2=J.|last3=Garcia|first3=E. F. J.|publisher=Cornell Lab of Ornithology|year=2020|location=Ithaca, NY, USA|chapter=Antarctic Tern (Sterna vittata)}}</ref>

In breeding plumage, the tern has light grey body and wings. Its deeply forked tail, lower back just above it and cheeks are white. It also has a distinctive black cap that reaches from the nape down to the bill and the eye is brownish-black. The bill, legs and feet are bright red. In non-breeding plumage, the black cap is reduced to just the area behind the eyes, the underparts become lighter and the bill becomes a dull reddish-black colour. Juveniles have yellowish-brown, grey, and white spots on their backs, with a yellowish-brown belly and breast. Their bill is dull black and the legs are dull red.<ref name=”:1″>{{Cite web|last=Sagar|first=P. M.|date=2013|title=Antarctic tern|url=http://www.nzbirdsonline.org.nz/species/antarctic-tern|access-date=2020-10-13|website=New Zealand Birds Online}}</ref> The chicks have a yellowish-brown colour with black spots on their heads and back. They have a greyish white belly with a darker throat. The bill, legs and feet can be flesh colored or reddish black.<ref name=”:0″ />

In breeding plumage, the tern has light grey body and wings. Its deeply forked tail, lower back just above it and cheeks are white. It also has a distinctive black cap that reaches from the nape down to the bill and the eye is brownish-black. The bill, legs and feet are bright red. In non-breeding plumage, the black cap is reduced to just the area behind the eyes, the underparts become lighter and the bill becomes a dull reddish-black colour. Juveniles have yellowish-brown, grey, and white spots on their backs, with a yellowish-brown belly and breast. Their bill is dull black and the legs are dull red.<ref name=”:1″>{{Cite web|last=Sagar|first=P. M.|date=2013|title=Antarctic tern|url=http://www.nzbirdsonline.org.nz/species/antarctic-tern|access-date=2020-10-13|website=New Zealand Birds Online}}</ref> The chicks have a yellowish-brown colour with black spots on their heads and back. They have a greyish white belly with a darker throat. The bill, legs and feet can be flesh colored or reddish black.<ref name=”:0″ />

==Habitat and Distribution==

==Habitat and Distribution==

[[File:Sterna vittata -St Andrews Bay, South Georgia, British Overseas Territories, UK -flying-8 (1).jpg|thumb|Antarctic tern flying over St Andrews Bay, South Georgia, British Overseas Territories|alt=]]

[[File:Sterna vittata -St Andrews Bay, South Georgia, British Overseas Territories, UK -flying-8 (1).jpg|thumb|Antarctic tern flying over St Andrews Bay, South Georgia, British Overseas Territories|alt=]]

The Antarctic tern prefers rocky areas such as islets, with or without vegetation, often among other seabird species. It usually nests on cliffs but is also found on rocky beaches, places inaccessible to cats or rats. It also avoids beaches with sea lions, as they tend to occupy all flat areas. Outside of the breeding season, this species of tern looks for ice edges in Antarctica. It also visits South Africa’s beaches and rocky cliffs.<ref name=”:0″ />

The Antarctic tern prefers rocky areas such as islets, with or without vegetation, often among other seabird species. It usually nests on cliffs but is also found on rocky beaches, places inaccessible to cats or rats. It also avoids beaches with sea lions, as they tend to occupy all flat areas. Outside of the breeding season, this species of tern looks for ice edges in Antarctica. It also visits South Africa’s beaches and rocky cliffs.<ref name=”:0″ />

This species has a large range, widely distributed around sub-Antarctic islands of the southern hemisphere and the Antarctic mainland. The breeding territory of the Antarctic tern includes the Antarctic continent, Bouvet Island, the French Southern Territories, Saint Helena, Ascension and Tristan da Cunha, South Africa, South Georgia, and the South Sandwich Islands.<ref name=”:4″>{{Cite iucn|last=BirdLife International|date=2019|title=Sterna vittata|url=https://www.iucnredlist.org/species/22694635/155620911|access-date=2020-10-13}}</ref> Recently, some populations have been found to take advantage of newly ice-free terrain on the north-eastern Antarctic Peninsula when nesting.<ref name=”:0″ />

This species has a large range, widely distributed around sub-Antarctic islands of the southern hemisphere and the Antarctic mainland. The breeding territory of the Antarctic tern includes the Antarctic continent, Bouvet Island, the French Southern Territories, Saint Helena, Ascension and Tristan da Cunha, South Africa, South Georgia, and the South Sandwich Islands.<ref name=”:4″>{{Cite iucn|last=BirdLife International|date=2019|title=Sterna vittata|url=https://www.iucnredlist.org/species/22694635/155620911|access-date=2020-10-13}}</ref> Recently, some populations have been found to take advantage of newly ice-free terrain on the north-eastern Antarctic Peninsula when nesting.<ref name=”:0″ />

=== Vocalizations ===

=== Vocalizations ===

Antarctic terns are quite noisy around their roost sites. “trr-trr-kriah” is their main call and is given when they are in flight or fishing.<ref name=”:0″ /> They also use a “chrrrr” to defend their nests against intruders or predators. They make a higher-pitched call to catch the attention of their mates.<ref name=”:1″ />

Antarctic terns are quite noisy around their roost sites. “trr-trr-kriah” is their main call and is given when they are in flight or fishing.<ref name=”:0″ /> They also use a “chrrrr” to defend their nests against intruders or predators. They make a higher-pitched call to catch the attention of their mates.<ref name=”:1″ />

=== Diet ===

=== Diet ===

The Antarctic tern is an opportunistic feeder that mostly eats small fishes as well as some [[crustacean]]s like [[Antarctic krill]].<ref name=”:0″ /> It usually fishes gregariously, forming flocks of up to 100 birds when they locate larger shoals.<ref name=”:1″ /> It fishes by hovering a few meters above the sea. When a prey is located, the tern has two strategies: most of the time it will directly plunge dive and become completely submerged but if the water is too rough it will only submerge its bill whilst in flight.<ref name=”:0″ /> It normally forages near the shore in the kelp zone.<ref name=”:2″ /> It has also been found in the intertidal zone, scavenging for small crustaceans, [[polychaete]]s, and [[shellfish]]. However, during the breeding season, it does not venture very far from its nest.

The Antarctic tern is an opportunistic feeder that mostly eats small fishes as well as some [[crustacean]]s like [[Antarctic krill]].<ref name=”:0″ /> It usually fishes gregariously, forming flocks of up to 100 birds when they locate larger shoals.<ref name=”:1″ /> It fishes by hovering a few meters above the sea. When a prey is located, the tern has two strategies: most of the time it will directly plunge dive and become completely submerged but if the water is too rough it will only submerge its bill whilst in flight.<ref name=”:0″ /> It normally forages near the shore in the kelp zone.<ref name=”:2″ /> It has also been found in the intertidal zone, scavenging for small crustaceans, [[polychaete]]s, and [[shellfish]]. However, during the breeding season, it does not venture very far from its nest.

== Threats and Conservation ==

== Threats and Conservation ==

The [[IUCN Red List]] classifies the Antarctic tern as a species of least concern in terms of conservation status.<ref name=”:4″ /> The population is stable and is currently estimated to be between 132,000–145,000 individuals, with about 45,000 breeding pairs. The majority are from the subspecies S. ”v. gaini.”<ref name=”:0″ />

The [[IUCN Red List]] classifies the Antarctic tern as a species of least concern in terms of conservation status.<ref name=”:4″ /> The population is stable and is currently estimated to be between 132,000 and 145,000 individuals, with about 45,000 breeding pairs. The majority are from the subspecies S. ”v. gaini.”<ref name=”:0″ />

However, reproduction failures have been recorded on certain islands mostly due to introduced mammalian predators, namely domestic cats and rats.

However, reproduction failures have been recorded on certain islands mostly due to introduced mammalian predators, namely domestic cats and rats.