Sooty Tern Onychoprion fuscatus 烏燕鷗
Category I. Accidental in coastal areas during the tropical storm season.
IDENTIFICATION
Jun. 2019, Ivan Tse.
36-45 cm. Most birds seen in HK are in their first year and are largely dark brown apart from the forecrown, underwing coverts and belly.
Jun. 2019, Michelle and Peter Wong. In flight the dark grey-brown breast contrasts with an off-white belly. Call also diagnostic (see below), but unlikely to be heard here. Adult similar to Bridled Tern but differs in slightly larger size, darker uniform upperparts from crown to rump, white forehead patch not extending past eye, dark underside to outer primaries and narrower white tail sides. |
VOCALISATIONS
The so-called ‘wideawake’ call is diagnostic.
DISTRIBUTION & HABITAT PREFERENCE
Mainly recorded at sea but exhausted birds have been picked up inland.
OCCURRENCE
Most records are of immature birds; extreme dates are 5 April to 20 October.
1995: singles on 3 October at Tin Shui Wai reclamation and near Cheung Chau during Typhoon Sibyl.
1997: one near Cheung Chau on 8 September.
1999: juvenile off Cape D’Aguilar during close approach of Typhoon York on 16 September.
2006: second calendar-year bird south of Po Toi on 2 May and juvenile off Po Toi on 13 September.
2009: second calendar-year bird in southern waters on 5 April 2009.
2015: second calendar-year bird near the Soko Islands on 24 May 2015.
2016: two first-year birds in outer Tolo Harbour during 3-5 August and a juvenile picked up in Hung Hom on 20 October that subsequently died in care.
2018: an adult picked up Fairview Park on 18 September that subsequently died in care.
2019: juvenile at Kung Chau during 1-2 June 2019.
2020: singles in Tolo Harbour on 31 May and the Tap Mun – Shek Ngau Chau area during 2-7 August.
BEHAVIOUR, FORAGING & DIET
Usually appears in association with tropical storms, mainly at sea but also inland where exhausted birds have been picked up.
RANGE & SYSTEMATICS
Occurs in tropical and subtropical oceans around the world, but particularly in the west Pacific from Japan southeast to Easter Island (Schreiber et al. 2020). In China there are records from offshore areas of eastern and southern coastal provinces, and from the central Yangtze area (Liu and Chen 2020).
Of the six subspecies recognised, O. f. nubilosus is presumed to occur in HK given that it breeds from the Indian Ocean east to the Ryukyus and south to the Greater Sundas. Five other subspecies are recognised, of which the most relevant is serratus, which breeds from Australia through New Guinea to the south Pacific.
CONSERVATION STATUS
IUCN: Least Concern. Population trend unknown.
Liu, Y. and Chen, Y. H. (eds) (2020). The CNG Field Guide to the Birds of China (in Chinese). Hunan Science and Technology Publication House, Changsha.
Schreiber, E. A., C. J. Feare, B. A. Harrington, B. G. Murray Jr., W. B. Robertson Jr., M. J. Robertson, and G. E. Woolfenden (2020). Sooty Tern (Onychoprion fuscatus), version 1.0. In Birds of the World (S. M. Billerman, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.sooter1.01
