Amphibians of Hong Kong
Amphibians are animals that spend part of their life in water and part on land. They comprise a group of animals with highly varied external morphology and habits, yet sharing some common characteristics. Amphibians are cold-blooded; they have a bare and usually wet skin, without any scales or hair; and, the most special feature, they have two distinct life phases. Amphibians hatch out as aquatic larvae (tadpoles), breathing through gills. As they mature, they typically develop lungs and legs by a processa called metamorphosis, so they are able to leave water and live on land.
The Hong Kong amphibians belong to either the Caudata (tailed amphibians) or the Anura (tail-less amphibians). The Caudates are characterized by an elongated body, a long tail and an apparent neck. They are aquatic or terrestrial. In Hong Kong , this group is represented by only one species: the Hong Kong Newt (Paramesotriton hongkongensis), which can be found in pristine mountain streams at all elevations.
The Anurans consist of frogs and toads. They have no true neck and the adults are tail-less. They spend their larval stage in water, but the adults are mainly terrestrial. Frogs generally have slippery skin, with webbing between their toes. They mostly live near water bodies and are good swimmers. In Hong Kong , there are 20 species of frogs, including the lately discovered South China Cascade Frog (Amolops ricketti) from Lantau Island. The local frogs differ greatly in size, from the tiny Romer's Tree Frog (Liuixalus romeri), which is about 1.5cm long to the huge Giant Spiny Frog (Quasipaa spinosa), which grows to over 14cm in length.
Toads generally have dry, warty skin and no webbing between their toes. In Hong Kong , there are three species of toads, including the common and widespread Asian Common Toad (Duttaphrynus melanostictus), which has poison glands on the sides of the head. The other two species, the Short-legged Toad (Xenophrys brackykolos) and the Leaf-litter Toad (Leptolalax laui), are confined to mountain streams.
The amphibian fauna of Hong Kong is rather diverse, accounting for 7 percent of the 366 amphibian species occurring in China. This is mainly attributed to the presence of a wide range of habitats, from the hillside streams to the low-lying wetlands (such as agricultural fields), offering suitable habitats to both upland inhabitants (e.g. Giant Spiny Frog, Leaf-litter Toad) and lowland dwellers (e.g. Marbled Pigmy Frog Microhyla pulchra, Spotted Narrow-mouthed Frog Kalophrynus interlineatus). Some widespread and abundant species, such as the Gunther's Frog (Hylarana guentheri) and Paddy Frog (Fejervarya limnocharis), can be found in different habitats at all altitudes. Among the 24 species recorded so far, only the Romer's Tree Frog is considered endemic to Hong Kong . The Hong Kong Newt and the Hong Kong Cascade Frog (Amolops hongkongensis) were once thought to be endemic to Hong Kong, but were later found in other places of Guangdong Province.
Despite their semi-terrestrial mode of life, amphibians are closely associated with water, because water bodies are their breeding ground. Rapid development in Hong Kong has resulted in the loss of many low-lying wetlands which were once important amphibian habitats, and this has led to a severe decline in the populations of certain lowland species (such as the Rough-skinned Floating Frog (Occidozyga lima), which inhabited the once-abundant, but no longer existing, paddy fields). The species was not found in recent surveys. The pollution of water bodies and acid rain would also affect individual's survival, particularly for the sensitive species, as the permeable skin of amphibians makes them highly susceptible to the pollutants. However, some hardier pollution-tolerant species, such as Gunther's Frog and the Asian Common Toad, are still common – and, even in disturbed habitats, widespread.
Regarding species conservation, Fellowes et al. (2002) identified 12 species of Hong Kong amphibians to be of conservation concern, either on a local, regional or global scale. The Herpetofauna Working Group (HWG) of the Agriculture, Fisheries and Conservation Department (AFCD) reviewed the conservation status of these species, taking into account the latest results from a territory-wide baseline survey undertaken by AFCD since 2002 and consultation with local herpetologists. With more up-to-date information, the review indicated that many species were under-recorded in the past, and revised the list of species of conservation concern. The species now considered to be of conservation concern include the Romer's Tree Frog and Giant Spiny Frog.
Romer's Tree Frog
Romer's Tree Frog is endemic to Hong Kong , that is, the species is found in Hong Kong but nowhere else in the world. It is the smallest frog in Hong Kong , distinguished by the X-mark on its back. The species occurs on Lantau Island , Lamma Island , Po Toi and Chek Lap Kok. Due to the construction of the Hong Kong International Airport, the population of Romer's Tree Frogs in Chek Lap Kok was collected, captive-bred and subsequently released to suitable habitats in the New Territories and Hong Kong Island. These translocated populations have been closely monitored, and the successful establishment of the released frogs has been confirmed. Romer's Tree Frog is now considered to have a secure population status. Protection of its major habitats, which mostly fell within existing protected areas or areas covered by conservation zonings on statutory land use plans, will safeguard the survival of Romer's Tree Frog. However, the tiny Romer's Tree Frog is still susceptible to threats such as degradation of suitable habitats. Dedicated conservation efforts, in particular species monitoring, will continue to ensure the conservation and survival of this endemic amphibian.
Giant Spiny Frog
Giant Spiny Frog is the largest frog in Hong Kong. Its distribution is confined to the mountain streams in Tai Mo Shan area, and it is listed as ‘Vulnerable' in IUCN Red List and China Red Data Book. Although the Giant Spiny Frog occurs inside Country Parks, in view of its highly restricted distribution, regular monitoring of the species and its habitats is considered essential for its continued survival in Hong Kong.
The Hong Kong Newt, Hong Kong Cascade Frog and Romer's Tree Frog are protected species listed under the Wild Animals Protection Ordinance (Cap.170). It is an offence to collect or disturb them or their eggs.
The local amphibians are well represented, either exclusively or partially, inside the existing protected areas such as Country Parks , Special Areas and Sites of Special Scientific Interest (SSSI). These protected areas include some of the important sites for local amphibians, thus safeguarding these sites against threats of development. For example, the seasonally inundated stream and the surrounding forest, plantation and shrubland in Ngong Ping, which are important breeding sites of the Romer's Tree Frog, have been designated as a SSSI. The streams and the surrounding habitats at Tai Mo Shan, which are the sole habitats for the rare Giant Spiny Frog in Hong Kong , are mostly within Country Park as well as SSSI.
Meanwhile, species action plans have been developed for the specific conservation needs of the amphibian species of conservation concern. At present, there are two amphibian action plans being implemented by AFCD, one for the Romer's Tree Frog and the other for the Giant Spiny Frog. A major component of the action plans is population monitoring, which includes regular checks of the occurrence of the species and the condition of their habitats.
Public education also plays an important role in conservation. AFCD has published "A Field Guide to the Amphibians of Hong Kong" to enhance public knowledge on this group of animals.
The effective camouflage and nocturnal habit of most frogs and toads make them difficult to see during the day, when they often hide among rocks and crevices, or under leaf litter and bushes. Frogs and toads usually stay near water, so marshes, ponds, streams or wet cultivation fields are good places to look for them. The best time of the year to observe frogs and toads is in the early wet season, when they are more active due to the onset of their breeding cycle. During the breeding season, male mating calls can be heard at dawn or dusk near streams, marshes, ponds and cultivated fields. Eggs and tadpoles can often be seen in water pools or ditches. One can also find egg mass of the Brown Tree Frog (Polypedates megacephalus) suspended on tree branches, or attached to the side of tanks and wells above water level.
The mating calls of different frog and toad species are quite distinct, and so surveying them by listening to their calls is effective during their breeding season. For example, the calls of Asiatic Painted Frog (Kaloula pulchra pulchra) resembles the sounds of cow mooing. During the colder months when it is difficult to encounter a frog or toad in the open wild, one may find them seeking refuge from the weep holes of man-made catchwaters.
Most of the frogs and toads hibernate when the temperature drops below
Karsen, S. J., Lau, M.W.N. & Bogadek, A. 1998. Hong Kong Amphibians and Reptiles (2nd Edition). A Provisional Urban Coun cil Publication.
Xie, F., Lau, M.W.N., Stuart, S.N., Chanson, J.S., Cox, N.A. & Fischman, D.L. 2007. Conservation needs of amphibians in China: a review. Sciene in China Series C: Life Sciences 50: 265-276.
Zhao, E. and Adler, K. 1993. Herpetology of China . Oxford , Ohio : Society for the Study of Amphibians and Reptiles in cooperation with Chinese Society for the Study of Amphibians and Reptiles.
趙 爾 宓 。 1998 。 中 國 瀕 危 動 物 紅 皮 書 - 兩 棲 類 及 爬 行 類 。 科 學 出 版 社 。
中 國 野 生 動 物 保 護 協 會 。 2000 。 中 國 兩 棲 動 物 圖 鑒 • 河 南 科 學 技 術 出 版 社 。
呂 光 洋 ， 杜 銘 章 ， 各 高 世 。 2002 。 台 灣 兩 棲 爬 行 動 物 圖 鑒 ( 第 二 版 ) 。 中 華 民 國 自 然 生 態 保 育 協 會 。 大 自 然 出 版 社 。
楊 懿 如 。 2002 。 賞 蛙 圖 鑑 。 中 華 民 國 自 然 生 態 攝 影 學 會 。