Radde’s Warbler Phylloscopus schwarzi 巨嘴柳鶯
Category I. Uncommon autumn passage migrant and scarce winter visitor to open-canopy shrubland and woodland, and forest edge.
IDENTIFICATION
Dec. 2022, David Stanton.
12.5-14 cm. Similar to Dusky Warbler but slightly larger and sturdier with a blunter and stouter bill, longer supercilium and thicker, paler, more orange-tinged legs. More olive above and buff below on flanks, vent and undertail coverts (especially on first-year birds), and slightly paler panel in closed wing. Supercilium buff (and less well-defined) above lores and whitish behind eye (usually the opposite on Dusky Warbler), with faintly dark upper border. For differences from Yellow-streaked Warbler, see that species.
VOCALISATIONS
The commonly-heard call is a nasal ‘chik’ or ‘chep’, softer and higher-pitched than Dusky Warbler.
The song, rarely heard in HK, is a trilling usually preceded by a few short introductory notes.
This is an example of low-intensity song on the wintering grounds.
DISTRIBUTION & HABITAT PREFERENCE
Most records of Radde’s Warbler are from areas of open woodland or shrubland. It has occurred at widespread sites including offshore island and urban edge sites such as Ho Man Tin, where it is a regular winter visitor. At Mai Po and on Po Toi there are very few records after the turn of the year indicating it is largely migrants that occur at these sites.
OCCURRENCE
Radde’s Warbler was first recorded in 1981 when one was present at Lam Tsuen on 31 October. It was again noted in 1985 and 1987 and has been nearly annual since 1990. It is now regarded as an uncommon passage migrant and scarce winter visitor. A greater understanding of the passage period and habitat preferences and increased observer coverage are the likely causes of the recent upsurge in records.
The earliest record in autumn concerns one trapped at Mai Po NR on 5 October 2019. Main passage occurs from the last week of October to the end of November, with numbers peaking in the third week of November (Figure 1). By the third week of December the wintering population appears to be established, and numbers decline slowly from the first week of March. The latest on record occurred at Ho Man Tin on 4 May 2016. Most records are of one to two birds, with the highest count being six at Mount Davis on 19 November 2012 and at Tai Lam Country Park on 5 November 2019.
BEHAVIOUR, FORAGING & DIET
Although less restless than Dusky Warbler it forages over a wider area and is more likely to make a long flight to a different foraging area. Due to this mobility, it is difficult to see well.
RANGE & SYSTEMATICS
Monotypic. Breeds in southeast Siberia from the Altai east to Kamchatka and thence south to North Korea; winters in coastal south China, Yunnan, southeast Tibet and Indochina (Clement 2020, Liu and Chen 2020).
CONSERVATION STATUS
IUCN: Least Concern. Population trend stable.
Figure 1.
Clement, P. (2020). Radde's Warbler (Phylloscopus schwarzi), 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.radwar1.01
Leader, P. J. (1995). Field identification of Dusky, Radde’s and Yellow-streaked Warblers. Hong Kong Bird Report 1994: 170-180.
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.
