Russet Bush Warbler Locustella mandelli 高山短翅鶯
Category I. Common winter visitor and autumn passage migrant; small breeding population present on higher mountain tops.
IDENTIFICATION
Dec. 2018, Koel Ko.
13-14 cm. Russet upperparts, ear coverts and flanks, pale-tipped undertail coverts and relatively long tail. Poorly-marked supercilium usually obvious only in front of and above eye. Undertail coverts are russet-brown with the longest having broad paler tips. Non-breeding birds have largely pale lower mandible.
Differs from Brown Bush Warbler in duller, darker upperparts, greyer throat, duller breast and belly, darker flanks, pale-tipped undertail coverts, slightly more obvious supercilium and, in breeding season, dark lower mandible and spotting on throat.
Jul. 2019, Matthew Kwan.
The whitish throat is more obvious when in song and there is indistinct spotting across lower throat in the breeding season (though this may be overlain by fluffed out throat feathers when in song). Breeding adults have black bills.
VOCALISATIONS
The typical call, frequently heard in winter, is similar to that of Brown Bush Warbler but appreciably higher in pitch.
Possibly given in alarm is a broadband rasping churr.
The full song, which consists of long stereotyped strophes, is more likely to be heard from March.
Low-intensity song is generally heard in the winter months and usually comprises shorter strophes and/or somewhat degraded elements.
In addition, a highly degraded song phrase or call is occasionally given.
DISTRIBUTION & HABITAT PREFERENCE
In the breeding season occurs above 500 m in dense grass, rank grass and dwarf bamboo on the Tai Mo Shan massif. There are a few records from Lantau Peak, Ma On Shan and Pat Sin Leng that suggest breeding may occur at these sites too. The relatively few breeding season records in other areas of apparently suitable breeding habitat may be due in part to a lack of observer activity.
In the non-breeding season can be found in a variety of dense grass and shrub-grass habitats on hillsides, fish pond areas, village edge and agricultural areas.
OCCURRENCE
It was not until birds were trapped at Ho Chung and Sha Lo Tung in 1992 that Russet Bush Warbler was accepted onto the HK List (Kennerley and Leader 1993). Previously, it was not certain which species was uttering the distinctive song, but it became clear that Russet Bush Warbler had been heard as early as 4-5 March 1987.
Winter visitor and autumn passage migrant, with a small breeding population on Tai Mo Shan. Numbers are highest from the second week of November to the third week of February (Figure 1), after which there is a departure that is more marked after the first week of March. From the last week of March to the first week of August most records concern breeding birds on Tai Mo Shan. It appears that non-breeding birds first appear in early September but remain rare until the third week of October.
The highest count outside the breeding season is nine at Sha Lo Tung on 10 November 2002.
BREEDING
A singing bird at Ho Chung on 10 April 1993 was the first record for that month; this was followed at Tai Mo Shan by a bird in song on 23 July 1995 and up to four in song there during 25-30 April 1997 indicating a breeding population was established. Since 1999 up to ten birds have been noted in song there in the breeding season. Juveniles have been seen during 13-17 July.
BEHAVIOUR, DIET & FORAGING
Typical of its genus, a highly skulking species that is generally only seen well when in song. Creeps through low dense vegetation as it forages and may be difficult to see even at very close range when only its voice indicates presence. Song is heard mainly from November to May, with no reports in September or October.
SYSTEMATICS & RANGE
The nominate subspecies breeds in the Himalayan foothills from Darjeeling through Sikkim to Bhutan and in northeast India in Arunachal Pradesh and southern Assam (Kennerley and Pearson 2010). The full extent of the breeding distribution of L. m. melanorhyncha is unclear, but it is known to breed in southeast China from Fujian through Guangdong and south Hunan west to Guangxi, south central Yunnan and southeast Sichuan, and in north Vietnam (Alström et al. 2015, Lewthwaite 1996). It is known in winter from HK and adjacent parts of Guangdong, suggesting it occurs throughout the coastal provinces of China at this time (Carey 2021).
CONSERVATION STATUS
IUCN: Least Concern. Population trend stable.
Figure 1.
Alström, P., C. Xia, P. C. Rasmussen, U. Olsson, B. Dai, J. Zhao, P. J. Leader, G. J. Carey, L. Dong, T. Cai, P. I. Holt, H. L. Manh, G. Song, Y. Liu, Y. Zhang, and F. Lei (2015). Integrative taxonomy of the Russet Bush Warbler Locustella mandelli complex reveals a new species from central China. Avian Research (2015) 6:9.
Carey, G. J. (2021). Russet Bush Warbler (Locustella mandelli), version 2.0. In Birds of the World (S. M. Billerman, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.rubwar1.02.
Kennerley, P. R. and Leader, P. J. (1993). Russet Bush Warbler and Brown Bush Warbler: two species new to Hong Kong. Hong Kong Bird Report 1992: 114-130.
Kennerley, P. and D. Pearson (2010). Reed and Bush Warblers. Christopher Helm, London.
Lewthwaite, R. W. (1996). Forest birds of southeast China: observations during 1984-1996. Hong Kong Bird Report 1995:150–203.
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.
