Thick-billed Warbler Arundinax aedon 厚嘴葦鶯
Category I. Scarce passage migrant in autumn, rare in winter and spring; occurs in diverse well-vegetated early succession or reed marsh habitats.
IDENTIFICATION
Sep 2021, Roman Lo.
16-17.5 cm. Relatively longer tailed and larger headed but slightly smaller than Oriental Reed Warbler. Notably bare-faced head pattern due to pale lores and ear coverts and very indistinct supercilium, both emphasized by large dark eye. Brown upperparts, warmer on rump, tail and crown, sometimes imparting a capped effect; crown feathers often raised. Dull white below with buff flanks. Bill deeply-based with a sharply decurved culmen.
Apr. 2021, Graham Talbot.
In flight has relatively short wings, long, full tail and rufous coloration on rump and tail.
VOCALISATIONS
The call is variable, but often sounds quite low in pitch and rather soft.
Also gives a rattling churr.
DISTRIBUTION & HABITAT PREFERENCE
Most records are of trapped birds at Mai Po NR where it generally occurs away from the reed beds in shrub and other dense vegetation. In the 1990s it was also trapped in closed-canopy shrubland at Kadoorie Agricultural Research Centre. It has also been recorded in shrub or shrub/grass at other sites in the Deep Bay area and elsewhere, including Po Toi. This species is not wetland-dependent, although it may occur in the dense wetland vegetation.
OCCURRENCE
The first record of Thick-billed Warbler was of two near Lok Ma Chau on 31 October 1982 (Chalmers 1984), which was followed by one at Mai Po on 15 October 1983. Although there were only four more records in the 1980s, ringing activities in the 1990s proved it to be a regular autumn migrant in small numbers.
Most records occur from the second week of September to the first week of November (Figure 1). The earliest autumn record was a bird trapped at Mai Po on 29 August 1992. It is rare from the second week of November, but it has been recorded in each week until the end of the year. There are only five records in the early part of the year, from 14 January to 3 March. Spring passage birds have been noted on only a few occasions from 4 April to 17 May.
BEHAVIOUR, FORAGING & DIET
Rather slow-moving when foraging and not easily seen well as it is reluctant to come into the open. May remain deep in vegetation when only occasional calls confirm its presence.
RANGE & SYSTEMATICS
The taxon considered to occur in HK is A. a. rufescens, which breeds in east Siberia, northeast Mongolia, northeast China and adjacent areas of Russia, and winters in south China and Indochina; the nominate subspecies breeds to the west in northwest Mongolia and south-central Siberia and winters in Nepal and east and south India east to Myanmar and Thailand (Dyrcz 2020). In China a summer visitor to the northeast and a winter visitor to the southwest (Liu and Chen 2020).
CONSERVATION STATUS
IUCN: Least Concern. Population trend decreasing.
Figure 1.
Chalmers, M. L. (1984). Systematic List for 1982. Hong Kong Bird Report 1981/1982: 52-86.
Dyrcz, A. (2020). Thick-billed Warbler (Arundinax aedon), 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.thbwar1.01.
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.
