Subject: A Crow Story: vanishing in China, common in Hong Kong [Print This Page]
Author: HKBWS WY Time: 4/08/2017 16:31 Subject: A Crow Story: vanishing in China, common in Hong Kong
A Crow Story: vanishing in China, common in Hong Kong
The Hong Kong Bird Watching Society
1 August 2017
With 550 bird species recorded in Hong Kong, many are little or never studied locally and regionally. Therefore, we cannot fully understand how common or rare one species could actually be if no systematic survey has been conducted. Also, a species could be apparently common in one place but this is only a local situation and overall it could be quite rare. Collared Crow (Corvus torquatus) could be an example of this case as a recent study reveals this crow species, once described widely distributed in China, is suffering from a population crash in most of its distribution range but thriving in Hong Kong.
The general public always has a conception that all crows must be all black. In fact, the Collared Crow has white feathers on its neck making it easily identifiable in the field. The literature states that it was a common resident in large parts of South China and northern Vietnam but about 10 years ago ornithologists became aware that this had changed. After consulting many ornithologists and conservationists in the region, this species has been found becoming scarcer in many areas and BirdLife International, the largest nature and bird conservation partnership, and IUCN decided to uplist this species as globally Near-threatened in 2004 owing to a recently moderately rapid population reduction. The story has continued as researchers based in Hong Kong and China paid extra attention to this pied bird on two aspects: one is current distribution and population and another is ecology and habitat utilization in its regular site(s).
Rare in China
One study led by Paul Leader, Director of AEC Ltd, collected recent distribution and population data in South China, He and his team recently published the findings of this study in an international peer-reviewed journal Forktail. Mr. Leader explained, “This is the first systematic global population estimate for this species. We found the largest population was in the Dabie Shan area, a conjunction with three provinces: Hubei, Hunan and Anhui with a total of 450 individuals recorded. Hong Kong was found to be the second most important area for this species with a peak count of 362
individuals recorded. Though this species could still be found in other provinces, it was absent in some areas such as Shandong, Shanxi and Shanghai, and crucially the total population was estimated at fewer than 2,000 individuals.”
“This species was described as common in literature but based on field surveys in Guangdong during 2003-2014 we found this species absent from vast areas of suitable habitat indicating that a previous population estimate based on the extrapolation of numbers in Hong Kong is flawed. The revised population estimate of fewer than 2,000 individuals, was substantially lower than the previous estimated 15,000-30,000 individuals. Hence, we actually propose to uplist the threatened category for this species from the Near Threatened to Vulnerable.”
Common in Hong Kong
This species drew rather little attention in China in the last century because it was believed to be common and widespread in its distribution and not threatened. Conversely, it has been observed more closely in Hong Kong and information collected by the HKBWS tells that this species could be wetland-dependent as many individuals were found along the coast. Two big flocks were regularly reported at the Mai Po Nature Reserve and at Ting Kok near Tai Po, where the highest counts are 173 and 117 respectively. At both sites, the birds were frequently found feeding in the fishponds, gei wais, tidal flats and roosting in mangrove and other tall trees that the birds could stay away from disturbance sources. Therefore, their long term survival in the territory ties on conservation of these habitats.
Mr. Yat-tung Yu, Research Manager of the HKBWS, said, “The findings from Mr. Leader and his team provided a strong reason for conducting local conservation projects that could make a global contribution to the conservation of this species. The HKBWS carries out conservation projects – Fishpond Conservation Scheme in Northwest New Territories, with support from the Environment and Conservation Fund. We work together with fishpond operators to maintain or even increase the ecological value of the commercial fishponds. The Collared Crow is a key species to maintain a healthy ecosystem in the fishpond areas because it is a scavenger.”
Yu continued, “Scavengers can help speeding up consumption of fish and animal carcasses and are an important component of the nutrient recycle. If the carcasses are left around fishponds then water quality may deteriorate. The Collared Crow, frequently feeds on dead fish around ponds, playing an important role to keep the fishponds clean. Data collected from systematic surveys also revealed that the Collared Crows are strongly associated with fishpond management practices that more Collared Crows were found in drained fishponds and their numbers increased with the extent of the exposed bottom and fishpond size.”
“Collared Crows showed higher preference to the Mai Po Inner Deep Bay Ramsar Site which is closed to the main roosting site in the mangrove at Mai Po than the other surrounding areas and also preferred larger fishponds,” Yu added. “Hong Kong has become a safe haven for this species because all the wild birds are protected by Hong Kong law and there are large areas of protected wetlands. By understanding the ecology of this species, we know how to manage and provide the best habitat in order to safeguard it for the long term.”
To act before it is too late
The new findings suggest this species is undergoing a large scale population decline in China and the reasons behind the decline were not totally understood. Information from China has not been well updated, life history of this species has not been studied in details and many aspects, e.g. breeding biology and home range, are virtually unknown. In Hong Kong, most of the Collared Crows live in the wetland areas that are facing high pressure through habitat changes and degradation. Furthermore, this species is less attractive and popular than other ‘star’ birds, such as Black-faced Spoonbill and it draws less attention to its threats and conservation status.
As a result, in order to prevent further declines of this special crow, “Research on the unknown aspects of this species must be conducted,” says Paul Leader. “The status of the Collared Crow can only be assessed adequately after obtaining more scientific information and identifying the key threats.” Yat-tung Yu also stresses, “Conservation of the existing fishponds and the habitat within must be strengthened because fishpond habitat is the key for the long term survival of the Collared Crow in Hong Kong. Raising public awareness of this species is also needed, and how the crows and their habitats in Hong Kong have been protected is a very useful experience to be shared with conservationists and the public in the region.”
Appendix 1: Collared Crow Fact Sheet
Collared Crow Corvus torquatus belongs to the family Corvidae. There are a total of 130 species under Corvidae, including some species of Magpie and Crow. Crows are under the genus Corvus. Many people would think Crows are only in black colour, in fact there are only 45 black species in genus Corvus. They are almost cosmopolitan except in south South America, Arctic and Antarctic. They are all in small to medium size (body length: 20-69cm). A total of 29 species were assessed as globally threatened and near-threatened, including 3 Critically Endangered, 4 Endangered, 8 Vulnerable and 14 Near Threatened.
In Hong Kong, there are only 5 species of crows, of which two are native residents: Collared Crow and Large-billed Crow Corvus macrorhynchos, and another resident species is introduced – House Crow Corvus splendens. . The remaining two species are rare winter visitors. Collared Crows are found along the coasts in Hong Kong and records come from many sites: Deep Bay, Tolo Harbour, Victoria Harbour (Kwun Tong, North Point), Tsing Yi, Sai Kung, Lamma Island, Lantau (Tai O), etc; Large-billed Crows are usually found in the wooded inland areas over Hong Kong Island and New Territories; the House Crow is restricted mainly in urban Kowloon
Collared Crow is a distinctive crow because most of plumage is black with contrasting wide white collar from nape, upper mantle and side of neck to lower breast. Below is a comparison to other two resident crows.
| Collared Crow|
| Large-billed Crow|
| House Crow|
| Body size|
| 46-59 cm|
| Plumage colour|
| Most of plumage is black with white on nape, upper mantle, side of neck and lower breast|
| All black|
| Most of plumage is black with medium grey on nape to mantle, side of neck and side of breast|
| Main habitat|
| Agricultural land, Riverine plains, wooded country near water or marshes, less frequent in town and cities|
| Forests and woodland, agricultural land, can be found in town and cities|
| Abundant in all human habitation including city-centre park, sprawling slums, coastal villages|
| IUCN threatened category|
| Near Threatened|
| Least Concern|
| Least Concern|
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