Styan's Grasshopper Warbler Helopsaltes pleskei 史氏蝗鶯
Category I. Scarce winter visitor and rare or scarce passage migrant.
IDENTIFICATION
Sep. 2013, Paul Leader.
15-16 cm. Larger, longer-tailed, notably longer-billed, duller and more uniform than Pallas’s Grasshopper Warbler. Unstreaked, plain grey-brown above (with very little rump contrast) and on ear coverts. Narrow whitish supercilium extends to base of bill, but eye stripe diffuse and poorly-marked, especially behind eye. Adults such as this are darker and colder than first-winter birds.
Sep 2022, Michelle and Peter Wong.
First-winter birds have yellow-washed supercilium, throat and upper breast, indistinct spots on lower throat and pale fringes to the uppertail coverts. Note how dark and grey this first-winter bird, which was in the shade of mangrove at Mai Po, appears compared to the adult in sunlight above.
VOCALISATIONS
The vocalisations are similar to Pallas’s Grasshopper Warbler though less structured and forceful. This difference is not so obvious in singing birds in HK, however, as the song of both is often low intensity. However, Styan’s Grasshopper Warbler is generally only heard singing in the mangrove at Mai Po NR, while Pallas’s Grasshopper Warblers sing in habitats such as reed marsh or the dense vegetation at the edge of inactive fish ponds.
The ‘pwit’ call is very similar to that of Pallas’s Grasshopper Warbler, while the downslurred rattle is less dry and slightly more musical.
DISTRIBUTION & HABITAT PREFERENCE
Most records occur at Mai Po NR, either trapped in the reed marsh or present in the mangrove. Away from Mai Po but still in the Deep Bay area there are records from HK Wetland Park, Lok Ma Chau MTRC Ecological Enhancement Area and the fish pond areas at Hoo Hok Wai and San Tin. The only record away from the Deep Bay area occurred on 30 September 2015 at Chek Lap Kok.
OCCURRENCE
Scarce winter visitor and rare or scarce passage migrant that is most often recorded from mid-February to the first week of May (Figure 1), partly due to the presence of vocalising birds in the mangrove at Mai Po NR. Extreme dates are 8 September 2016 and 12 May in 1998 and 2016. The highest count is three, recorded on several dates from 14 March to 6 May.
The highest number of records in a single week is five in the third week of April. While this and Figure 1 suggest passage, it is of note that some birds trapped at other times in April had previously been trapped in midwinter, and others that were in active moult are also unlikely to have been freshly arrived migrants (Kennerley and Leader 1993).
BEHAVIOUR, FORAGING & DIET
Shy and skulking, as is typical of the genus. Often nervously flicks it wings. In mangrove areas it can be seen more easily than in reed marsh, and in both forages on the ground or at the base of plants. Song can be heard in the mangrove mainly in April and May but is rarely reported in the first three months of the year.
RANGE & SYSTEMATICS
Monotypic. Breeds on small islands in Peter the Great Bay, off the coast of South Korea and east China and off south Japan, including on the Izu Islands; the only known wintering sites are HK and the Red River Delta, Vietnam (Pearson 2021, Liu and Chen 2020).
CONSERVATION STATUS
IUCN: VULNERABLE. Population size 2,500-9,999 and decreasing due to wetland destruction in wintering areas and habitat loss on breeding grounds. As one of only two known wintering sites, the population at Mai Po NR should be considered globally important.
Figure 1.
Kennerley, P. R. and P. J. Leader (1993). Identification of Middendorf’s and Styan’s Grasshopper Warbler. Dutch Birding 15: 241-248.
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.
Pearson, D. (2021). Pleske's Grasshopper Warbler (Helopsaltes pleskei), version 1.1. 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.plewar1.01.1.
