The black-naped tern (Sterna sumatrana) is an oceanic tern mostly found in tropical and subtropical areas of the West-Pacific and Indian Oceans. They are rarely found inland.[2]
| Black-naped tern | |
|---|---|
| |
| S. s. sumatrana Ko Bi Da Island, off Phi Phi, Thailand | |
Scientific classification 
| |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Aves |
| Order: | Charadriiformes |
| Family: | Laridae |
| Genus: | Sterna |
| Species: | S. sumatrana
|
| Binomial name | |
| Sterna sumatrana Raffles, 1822
| |
The Black-naped tern is named for the black band beginning at the eyes connecting behind the head and descending the back of the neck. The rest of their plumage is a grey-white colour while their beaks and legs are black. They have a body length of 33-35cm and a wingspan of 66cm. Adults weigh between 97-120g. Hatchlings are a motled brown colour.[3][4]
Taxonomy
editThere are two listed subspecies:[3]
- S. s. mathewsi (Stresemann, 1914) – islands of the western Indian Ocean
- S. s. sumatrana (Raffles, 1822) – islands of the eastern Indian Ocean through to the western Pacific & Australasia
Distribution & Habitat
editThe Black-naped tern inhabits rocky shores throughout the Western-Pacific and Indian oceans, migrating yearly to islets and islands serving as breeding grounds.[5]
Behaviour
editHunting & Diet
editLike most terns, this species hunts by diving; they partially breach the surface of the water and directly capture their prey carrying it horizontally in their beak. Most hunt alone at sea, but hunt closer to shore in the surf when feeding nestlings and mates.[2]
Diet
editThe Black-naped tern diet consists of small fish up to 10cm long including those in families:[2]
- Atherinidae (hardyheads and sprats);
- Engraulidae (anchovies);
- Hemiramphidae (garfish);
- Exocoetidae (flying fish);
- Mugilidae (mullet);
- Sphyroenidae (barracudas);
- Carangidae (trevally or jacks);
- and Scombridae (tuna).
Reproduction & Development
editBreeding Grounds
editThe Black-naped tern breeds on oceanic islands in small colonies of 5-20 pairs, occasionally up to 200. Nests are made past high tide in depressions in sand or rock, sometimes delineated with shells or coral fragments, otherwise with little preparation. The rocky outcrops may be returned to yearly during the breeding season.[6]
Laying period
editLaying time varies from May to December depending on the location of the colony. Egg laying begins in India and Polynesia in May, followed by colonies in the Philippines in July, North-East Australia in September, oceanic Indian colonies from September-November, and the Great Barrier Reef from November-December. Leading up to egg laying, the male feeds the female her daily requirement of fish.[6]
Clutch Size & Brooding
editClutch size varies from island to island, between 1-3 eggs per pair. Both mates take shifts incubating the eggs for 21-23 days; shifts last anywhere between 4 minutes and 7 hours. Once the chicks hatch, the mates alternate in feeding and brooding for the first 7 days. As the chicks reach later stages of development, the mates hunt simultaneously.[6]
Predation
editUntil the chicks reach a weight of roughly 65g, they are vulnerable to predation by gulls; at this point, they are too large for the gulls to carry. Development to this weight takes 10.5 days; since the parents protect their nest for the first 7 days, chicks spend 3.5 days more vulnerable to predation. To defend against this, parents camouflage the nest by removing eggshell remnants and defecating several meters away to avoid bright eye-catching material near the chicks. When aerial predators are present, chicks hide themselves among vegetation and debris.[6]
On one occasion, a colony of Black-naped terns were observed using mobbing, shrill cries, and defecation as defence mechanisms against an encroaching Grey Heron during the breeding season.[4]
Fledging
editChicks fledge after 21-23 days; however, fledglings rely on their parents for at least 2 months afterwards. Parents and fledglings therefore leave breeding grounds together.[6]
Vocalizations
editThis tern calls with short, high-pitched, repeated sharp notes; "chit", "chip", "chrrut", "tsip"[3].
References
edit- ^ BirdLife International (2018). "Sterna sumatrana". IUCN Red List of Threatened Species. 2018: e.T22694612A132561758. doi:10.2305/IUCN.UK.2018-2.RLTS.T22694612A132561758.en. Retrieved 12 November 2021.
- ^ a b c Smith, Geoffrey C. (1990). "Factors Influencing Egg Laying and Feeding in Black-naped Terns Sterna Sumatrana". Emu - Austral Ornithology. 90 (2): 88–96. doi:10.1071/MU9900088. ISSN 0158-4197.
- ^ a b c Gochfeld, Michael; Burger, Joanna; Garcia, Ernest (2020). "Black-naped Tern (Sterna sumatrana), version 1.0". Birds of the World. doi:10.2173/bow.blnter1.01species_shared.bow.project_name. ISSN 2771-3105.
- ^ a b Deng, S. H.; Lee, T. K.; Wee, Y. C. (2008). "Black-naped tern (Sterna sumatra Raffles, 1822) mobbing a grey heron (Ardea cinerea Linnaeus,1758)" (PDF). Nature in Singapore (1): 117-127.
- ^ Thiebot, Jean-Baptiste; Nakamura, Noboru; Toguchi, Yutaka; Tomita, Naoki; Ozaki, Kiyoaki (2020). "Migration of black-naped terns in contrasted cyclonic conditions". Marine Biology. 167 (6): 83. doi:10.1007/s00227-020-03691-0. ISSN 1432-1793.
- ^ a b c d e Hulsman, Kees; Smith, Geoffrey (1988). "Biology and Growth of the Black-naped Tern Sterna Sumatrana: An Hypothesis to Explain the Relative Growth Rates of Inshore, Offshore and Pelagic Feeders". Emu - Austral Ornithology. 88 (4): 234–242. doi:10.1071/MU9880234. ISSN 0158-4197.
External links
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