Alstrom’s Warbler Phylloscopus soror 純色尾鶲鶯
Category I. Scarce to rare passage migrant in autumn and early winter to wooded areas with understorey.
IDENTIFICATION
Oct. 2019, Michelle and Peter Wong.
11-12 cm. Relatively large bill, orbital ring yellow and unbroken. Forehead and forecrown usually greenish meaning that blackish and pale grey on crown reaches only to area above eye. Lower border of lateral crown stripes has little grey, sometimes entirely olive-green, yellow underparts sometimes with greenish flanks, greater covert wing bar usually lacking (though may be faint or distinct) (Alström 2020, Leader and Carey 2016). Call diagnostic (see below).
VOCALISATIONS
The call is higher-pitched than its congeners, disyllabic and often loud and repeated: ‘chi-dit’ or ‘chi-tik’.
DISTRIBUTION & HABITAT PREFERENCE
Favours closed-canopy woodland but has also occurred at sites such as Mai Po NR car park, Po Toi and Tung Lung Chau.
OCCURRENCE
The first record occurred on 9 October 2004 (Wong and Wong 2011) but the second did not occur until 16 October 2011. It was subsequently recorded in late September and October 2012, November 2015, September 2016 and in each winter period since 2018/19. It remains scarce to rare, however, though this may change as an increasing number of observers become familiar with its call and appearance.
Extreme dates are 30 September and 27 December, indicating that most birds are probably passage migrants.
Lack of knowledge regarding field identification of members of the ‘golden-spectacled’ group of warblers means only in-hand records before 2002 can be assigned to species.
BEHAVIOUR, FORAGING & DIET
Forages unobtrusively in understorey when it takes short flights to catch insects; has a rather horizontal posture much of the time.
RANGE & SYSTEMATICS
Monotypic. Breeds in scattered areas from south Sichuan northeast to Shaanxi and Beijing, as well as areas in Fujian, Henan and Hunan; winters in southwest China and Indochina (Liu and Chen 2020).
CONSERVATION STATUS
IUCN: Least Concern. Population trend stable.
Alström, P. (2020). Alström's Warbler (Phylloscopus soror), 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.pltwar1.01
Leader, P. J. and G. J. Carey (2016). The identification of Seicercus warblers in Hong Kong. Hong Kong Bird Report 2014: 322-333.
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.
Wong, M. and P. Wong (2011). Plain-tailed Warbler Seicercus soror at Tai Po Kau. The first Hong Kong record. Hong Kong Bird Report 2007-08: 265-267.
