Baikal Bush Warbler Locustella davidi 北短翅鶯
Category I. Rare winter visitor and autumn passage migrant.
IDENTIFICATION
Feb. 2017, John and Jemi Holmes
12 cm. Rather uniform and lacking in distinctive features apart from broad whitish tips to undertail coverts that can form a banded pattern and are generally easily seen side-on. Relatively short tail among its congeners. Warm or olive-brown upperparts, pale supercilium more obvious above the lores where there is a dark spot just in front of the eye. Throat white, underparts pale greyish-brown, darker on flanks. Subdued spotting on the lower throat can be seen midwinter, but after pre-breeding moult these become rows of blackish spots. Of the two subspecies the nominate is warmer and richer brown above (Kennerley and Pearson 2010).
Upperparts duller but paler than Russet Bush Warbler, while both upperparts and underparts darker and duller than Brown Bush Warbler, in both of which the throat marks are absent or more restricted. Similar to Chinese Bush Warbler but latter has only narrow, often poorly-defined pale tips to the undertail coverts, duller upperparts, plainer head pattern and lacks throat spotting.
VOCALISATIONS
A vocal species from which a number of sounds have been heard in HK. The usual call is a ‘chak’ that is often repeated frequently and is very similar to a call of Lanceolated Warbler L. lanceolata.
A sharp ‘pwit’ is given in alarm.
Apparent calls of excitement similar to the following are occasionally heard.
The song is a series of regularly repeated short insect-like buzzing phrases that are approximately 0.5 seconds in duration and even in pitch.
DISTRIBUTION & HABITAT PREFERENCE
Most birds are found in mist nets, but it has also been recorded in podium level landscaping at Telford Garden, Kowloon Bay and in dense grassy vegetation at Yi O (Lantau), Po Toi and Tsung Yuen Ha.
OCCURRENCE
Rare winter visitor and autumn passage migrant. Extreme dates are 5 September 2014 and 28 April 2014.
The first record was of a bird trapped at Mai Po NR on 30 January 2004 and again three months later on 28 April (Leader 2009). Eight further birds were trapped up to January 2015 and it has been recorded in most winter periods since 2016/17. Aside from the first record, which concerned a bird that remained for three months, the other long-staying birds remained at Telford Garden, Kowloon Bay from 20 January to 20 February 2017 and at Mai Po NR from 7 December to 26 April 2018, where it was in song in the reedbed. Thus, it is clear that some birds do spend the winter in HK, though there are also a number of single-date records in September and October that are presumed passage migrants.
BEHAVIOUR, DIET & FORAGING
As with other members of the genus skulking and difficult to see, though perhaps slightly easier than many. Forages on the ground or in the lower branches of plants. Has been recorded in song from early December to late April.
SYSTEMATICS & RANGE
The nominate subspecies breeds from southeast Transbaikalia east to Heilongjiang in China and adjacent parts of Russia, and thence southwest as far Sichuan north of the Yangtze River. L. d. suschkini breeds in low montane areas of south Siberia from west Transbaikalia west to the Sayan and Russian Altai mountains. Winter distribution poorly known. The taxon suschkini winters in north Thailand and the species is presumed to breed in north Indochina into southwest China (Kennerley and Pearson 2010, Liu and Chen 2020).
CONSERVATION STATUS
IUCN: Least Concern. Population trend stable.
Kennerley, P. and D. Pearson (2010). Reed and Bush Warblers. Christopher Helm, London.
Leader, P. J. (2009). Baikal Bush Warbler Bradypterus davidi at Mai Po. The first Hong Kong record. Hong Kong Bird Report 2003-04: 210-214.
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.
