Plain Prinia Prinia inornata 純色鷦鶯
Category I. Locally common resident in grassy habitat mainly in the northwest New Territories.
Oct. 2010, Ivan Tse.
11 cm. Very small with a long, graduated tail that is shorter and less graduated during the breeding season. Upperparts largely plain brown with short darker streaks on the crown; wings are slightly darker. Face rather pale, including the lores, which are connected to a relatively broad buff supercilium that reaches to the back of the eye or slightly beyond. Underparts uniform whitish to buff. Tail brown with faint, darker subterminal marks and narrow, diffuse pale tip.
Distinguished from Yellow-bellied Prinia by more uniform plain brown upperparts, less contrast on the underparts and pale lores joined to a broad pale supercilium that ends at the rear of the eye and imparts a more open-faced expression; the bill shows a more obvious pale base in the non-breeding season.
The full song is a moderately high-pitched, monotonous, somewhat ringing and slightly clipped ‘teep-teep-teep….’, with each note repeated about five times a second. The pitch varies somewhat but generally lies in the range 4-6kHz. Phrases may last for 30 seconds or more.
Like its congener Yellow-bellied Prinia, it also does wing-snapping, as can heard in this recording of rather desultory song.
In interactions with other birds may utter a clipped ‘pwit’.
Also when interacting excitedly with other birds, and possibly in alarm, it utters a buzzing ‘dzeep’.
The call of alarm appears to be a high-pitched, short trill (T5374).
The begging juvenile gives a high-pitched, sharply downslurred ‘tsee’, which can be heard in this recording with the adult responding with the buzzing call.
DISTRIBUTION & HABITAT PREFERENCE
Plain Prinia occurs in lowland grassland areas and wetlands where there is grassy or reedy vegetation. The stronghold is the Deep Bay area where the grassy bunds of fish ponds and natural watercourses provide suitable habitat. It is absent from most offshore islands, unlike Yellow-bellied Prinia.
Between the 1993-96 and 2016-19 breeding bird atlases there was an increase in the percentage of occupied squares from 8.2% to 10.8%; this was also apparent in the winter atlas surveys of 2001-05 and 2016-19 between which there was an increase from 9.3% to 11.8%. However, a somewhat mixed picture is presented by these surveys. Breeding season occupancy was recorded in a higher number of 1km squares on Lantau, and the western New Territories in the Tai Lam area; however, in the Clearwater Bay peninsula, the northeast New Territories and the core part of the range in the Deep Bay hinterland there was a fall in the number of occupied squares. In the non-breeding season there were increased numbers recorded on Lantau, the Tai Lam area and, to a lesser extent Sai Kung. Areas at Ma On Shan alongside Tolo Harbour saw a decline. The decline in the Ma On Shan area is no doubt to new town expansion in previous waste ground areas of newly-reclaimed land. It appears to be on the verge of disappearing from HK Island where Chalmers (1986) stated it to be present in the southern part.
However, the increase overall is difficult to explain in the context of ongoing development in marginal areas of villages in the New Territories and Sai Kung and the maturation of grassland to shrubland in other areas. It appears likely that stochastic factors associated with the surveys may have resulted in an increase in some areas that is only apparent, not real.
The highest count reported is 91 birds at Tai Sang Wai and Lut Chau on 26 March 2015. Areas of inactive or abandoned fish ponds tend to be favoured due to lack of vegetation management, which allows long grass to remain.
Although long-term trapping at Mai Po NR indicates Plain Prinia is typically sedentary, there is evidence of movements in the form of records at the former airport at Kai Tak (Melville 1980), the current airport at Chek Lap Kok, where it has been recorded in most months of the year, with a high count of five. On Po Toi it appears to be a slightly erratic winter visitor from the second half of August to the end of May, with more records before the turn of the year; April and May records may involve migrants. The peak count on the island is five birds. It has also been recorded in the country park enclave of Pak Sha O, Sai Kung.
Swinhoe (1861), Kershaw (1904), and Herklots (1953) noted is as a common resident, although Dove and Goodhart (1955) only recorded it from August to May.
Breeding activity has been noted from late March to 1 August (carrying of nest material noted on the latter date). Adults feeding young have been recorded from 29 March to 7 June.
BEHAVIOUR, FORAGING & DIET
Has only been recorded feeding on insects and their larvae.
Occurs in similar fish pond areas as Yellow-bellied Prinia but is usually somewhat less obvious as it usually occurs at lower densities and is less demonstrative. Forages unobtrusively. Delivers song from the top of stems of grass or other vegetation, and also from overhead wires.
RANGE & SYSTEMATICS
Occurs from the Indian subcontinent east through Indochina to south China (Madge 2020), including Taiwan and Hainan. In China occurs from Yunnan and southern Sichuan northeast through Chongqing to Henan and southern Hebei, and areas south, including Hainan and Taiwan (Liu and Chen 2020).
P. i. extensicauda occurs in northern Indochina and south China, including HK. Nine other subspecies are also recognised.
IUCN: Least Concern. Population trend stable
Dove, R. S. and H. J. Goodhart (1955). Field observations from the Colony of Hong Kong. Ibis 97: 311-340.
Herklots, G. A. C. (1953). Hong Kong Birds. South China Morning Post, Hong Kong.
Kershaw. J. C. (1904). List of birds of the Quangtung Coast, China. Ibis 1904: 235-248.
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.
Madge, S. (2020). Plain Prinia (Prinia inornata), 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.plapri1.01
Melville, D. S. (1980). The birdstrike problem at Kai Tak Airport, Hong Kong. Final summary report 1974-1979. Agriculture and Fisheries Department, Hong Kong.
Swinhoe, R. (1861). Notes on the ornithology of Hong Kong, Macao and Canton, made during the latter end of February, March, April and the beginning of May 1860. Ibis 1861: 23-57.