Booted Warbler Iduna caligata 靴籬鶯
Category I. Accidental in open-country areas.
IDENTIFICATION
Jan. 2022, Michelle and Peter Wong.
11.5 cm. Rather small (slightly larger than and similar in structure to Common Chiffchaff), plain brown above often with a notably greyish tinge later in the winter; underparts off-white with buffish tinge to flanks. Pale supercilium is more obvious in front of eye, becoming diffuse behind, with a narrow dark border usually visible above this. There is obvious contrast between the grey-brown centres to the tertials and the paler fringes, which do not cover the whole of the outer web. The outermost tail feather has a narrow whitish outer edge.
Birds in their first autumn lack the warm coloration of fresh adults but have a buff wash to the face, breast and flanks. Underside of lower mandible at tip has a dark patch.
Oct. 2018, KWOK Tsz Ki
Some birds have a distinctive ‘milky tea’ coloration.
VOCALISATIONS
The typical and most distinctive call is a slightly muffled ‘chrk’.
DISTRIBUTION & HABITAT PREFERENCE
Has occurred in open-country habitats at Long Valley and the Deep Bay area.
OCCURRENCE
2015: one at Mai Po NR from 27 November to 24 December.
2016: one trapped at Mai Po NR on 23 September and one at San Tin from 28 December to 6 January 2017.
2018: one at San Tin on 14 October.
2019: one at Tai Sang Wai during 5-8 April.
In addition, an Iduna warbler at Long Valley during 14-15 September 1998 was either Booted or Sykes’s Warbler I. rama.
BEHAVIOUR, FORAGING & DIET
Usually shy, often foraging in low vegetation or small bushes; readily forages on ground. Insectivorous. Frequently flicks tail and wings.
RANGE & SYSTEMATICS
Monotypic. Breeds from west Russia east through southwest and south Siberia and the northern half of Kazakhstan to northwest Mongolia; winters in India (Svensson 2020). In China a summer visitor to northern Xinjiang and northwest Nei Monggol, with a few scattered accidental records on the east and southeast coast (Liu and Chen 2020).
CONSERVATION STATUS
IUCN: Least Concern. Population trend increasing.
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.
Svensson, L. (2020). Booted Warbler (Iduna caligata), 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.boowar1.01.
