Lesser Frigatebird Fregata ariel 白斑軍艦鳥
Category I. Occasional visitor to inshore and offshore sea areas.
IDENTIFICATION
In HK, size appears to be a convenient feature to identify Lesser Frigatebirds as they often associate with Black Kite either at roost or when soaring. In comparison, Lesser Frigatebird appears slightly larger or similar in size, whereas other frigatebirds are significantly larger.
Identification of frigatebirds is complex, and the full variation cannot be covered here. Readers are referred for further details to James (2004), from which the following is taken.
Mar. 2021, Morten Lisse.
Juvenile has triangular white belly patch, whitish axillary spurs angled outwards and originating near line of breast band and moderate buff alar bars.
Males: adult and 4th year birds have black underparts with whitish axillary spurs; 3rd years have black belly point and whitish axillary spurs; 2nd years have mottled black belly point and triangular axillary spurs angled outwards and moderate alar bars.
Females: adult and 4th years have black throat, white hind collar, black belly point, white triangular axillary spurs angled outwards and moderate whitish axillary spurs; 3rd years have black ring around neck, mottled black point on lower belly and prominent triangular axillary spurs.
VOCALISATIONS
Usually silent away from breeding colony (Orta et al. 2020); no vocalisations reported in HK.
DISTRIBUTION & HABITAT PREFERENCE
Recorded throughout HK usually over inshore or offshore waters, but occasionally at inland sites.
OCCURRENCE
Lesser Frigatebird was not reported prior to 1983 when an adult female was found dead at Island School, Mid-Levels on 11 September after the passage of Typhoon Ellen. Since then, whilst remaining scarce, it has established itself as the most frequent of the three frigatebird species to occur in HK.
Figure 1 shows that since 1999 most records have been in the period from April to late August, with extreme dates of 17 January 2012 and 25 November 2020. It occurs annually on average, though there were no records at all from April 2001 to April 2008.
All accepted records are of juveniles or immatures except for the adult female in 1983 and an adult male on 27 May and 18 June 1989. Long-staying birds have occurred, often roosting with Black Kites (e.g., from 8 April to 12 August 1988, with two there on the last date, and from 27 December 1991 to 26 August 1992).
BEHAVIOUR, FORAGING & DIET
Occasionally birds join the large Black Kite roost at Magazine Gap or other roost sites and may remain for a number of weeks.
RANGE & SYSTEMATICS
Breeds mainly in tropical areas of the Indian and Pacific Oceans, but prone to wandering as far north as southern Japan (Orta et al. 2020). In China a rare visitor to eastern and southern sea areas with scattered records inland (Liu and Chen 2020).
Three subspecies are recognised of which the nominate breeds from the east Indian Ocean to the central Pacific and is presumed to occur in HK.
CONSERVATION STATUS
IUCN: Least Concern. Population trend decreasing.
Figure 1.
James, D. J. (2004). Identification of Christmas Island, Great and Lesser Frigatebirds. BirdingASIA 1: 22-38.
Liu, Y. and Y. H. Chen (eds) (2020). The CNG Field Guide to the Birds of China (in Chinese). Hunan Science and Technology Publication House, Changsha.
Orta, J., E. F. J. Garcia, G. M. Kirwan, P. F. D. Boesman, and C. J. Sharpe (2020). Lesser Frigatebird (Fregata ariel), version 1.0. In Birds of the World (J. del Hoyo, A. Elliott, J. Sargatal, D. A. Christie, and E. de Juana, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.lesfri.01
