Common Myna Acridotheres tristis家八哥
Category IIB. Locally common resident population considered to derive from ex-captive birds.
IDENTIFICATION
May 2013, CHUNG Wing Kin.
23–26 cm. Adults have dark brown body, black head and yellow bill, feet and skin behind and below eye. Unlike Crested Myna, flanks and lower breast dark brown, fading on lower belly to white undertail coverts. Conspicuous white wing patches and underwing coverts in flight.
Sexes alike but male slightly larger than female. Juveniles duller and browner than adult with browner head feathers lacking gloss, brownish-black chin to upper breast and narrower duller pale tips to tail feathers.
VOCALISATIONS
In common with other members of the genus, a diverse array of sounds is given.
DISTRIBUTION & HABITAT PREFERENCE
Locally common in farmland, fishponds and other open country or village-edge areas with a low density of trees and vegetation, largely in the New Territories. Similar to Crested Myna, it generally avoids forest, closed-canopy shrubland and mountainous areas.
Common Myna was first recorded at Mong Tseng on 26 January 1952 (Herklots 1967) and became regular in the Ping Shan and Mong Tseng areas in the 1950s, occasionally in flocks of up to 30. While there appeared to be a decline in 1960s, a population became established in the vicinity of Shek Kong village and the nearby airstrip, where breeding was observed on military buildings between 1979 and 1981 with up to 23 birds feeding on the airstrip perimeter. After the conversion of the airfield to a refugee camp in the 1980s, good numbers were noted at Kam Tin, where the sizeable area of damp grazing pasture provided a suitable foraging area. Range expansion was noted in the 1990s, with breeding noted at Mai Po, Sheung Uk Tsuen and Sheung Shui in 1994.
While most of the early records were from the central New Territories, in the early 2000s the population had expanded northward, with Long Valley and fishponds in the northwest New Territories from Tai Sang Wai to San Tin supporting the largest number. Expansion further east as far as Tai Mei Tuk also occurred but the numbers involved were much lower. Signs of colonisation of Lantau were noted at Pui O from July 2015. There have also been a few sightings in urban parks including Kowloon Tsai, Mei Foo and Mong Kok.
There was a 68% range increase between the breeding bird surveys of 1993-96 and 2016-19 (recorded in 2.4% of surveyed grid squares in the earlier survey and 4.0% in the later). Similarly, a 74% range increase occurred between the winter atlas surveys of 2001-05 and 2016-19 (from 2.0% of the surveyed grids to 3.5%). Despite a reduction in the area of open habitats in the New Territories in the last two decades, Common Myna has managed to expand its range within the available habitats.
OCCURRENCE
Common Myna is a sedentary species with no known migratory movements. The population in HK is derived from captive origin and has naturalised successfully with no sign of decline; as a result, it is placed in Category IIB.
The highest count since 1999 is 63 birds at San Tin on 25 January 2018. Other high counts include 60 at Shek Kong on 15 November 2019 and 53 at Tai Kong Po on 22 February 2017. Smaller populations are present at other localities: up to 30 at Long Valley, ten at Tai Mei Tuk and 16 on Cheung Chau.
BEHAVIOUR, FORAGING & DIET
Like others in its genus, Common Myna is sociable and gregarious, readily forming evening roosts often with Crested Myna. It is opportunistic when foraging and frequently feeds on the ground together with Crested Myna. However, although omnivorous there are few local data regarding diet.
BREEDING
Breeding sites are mostly in man-made structures, including roofs, electricity pylons and behind air-conditioning units. Earliest nest-building was observed on 20 January and the latest on 29 April). Juveniles are seen from April to September.
RANGE & SYSTEMATICS
Two subspecies. The population in HK is considered derived from ex-captive individuals, probably of the nominate taxon, which naturally occurs in Turkmenistan, Uzbekistan, Kazakhstan, northwest China (Xinjiang), Kyrgyzstan and Tajikistan to Iran, Afghanistan and almost the entire Indian Subcontinent south of the Himalayan foothills (except Sri Lanka), thence east to Myanmar, south China (Yunnan and Hainan), Thailand, Indochina, Malay Peninsula and Singapore (Kannan and James 2020). It has been introduced both deliberately and accidentally to many parts of the world.
CONSERVATION STATUS
IUCN: Least Concern. Population trend increasing.
Herklots, G. A. C. (1967). Hong Kong Birds (2nd ed.). South China Morning Post, Hong Kong.
Kannan, R. and D. A. James (2020). Common Myna (Acridotheres tristis), version 1.0. In Birds of the World (S. M. Billerman, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA.
