Philautus romeri in Hong Kong: a frog re-introduction to a degraded tropical landscape.
by David Dudgeon and Michael Lau.
Much has been made of Hong Kong's endemic tree frog, Philautus romeri. With the recent completion of Michael Lau's Ph.D. thesis on this animal, we take the opportunity to revisit research on P. romeri in order to summarise what has been done, what we have learned, and why it is important.
The Special Administrative Region of Hong Kong includes the most densely populated urban conurbation in the world. The area has experienced centuries of human impact, and the original forest cover disappeared over 400 years ago. Despite past and ongoing human impacts, Hong Kong is host to 23 species of amphibians; 22 of them are anurans, and one - Philautus romeri (Rhacophoridae) or Romer's frog - is endemic. This tiny frog (adults are less than 2 cm long) was first discovered in 1952 by John D. Romer who found a population breeding in a small cave on Lamma Island. These individuals were apparently wiped out when the roof collapsed in 1953. The frogs were not rediscovered on Lamma until 1984 and, since then, they have been recorded at a few other localities. Extensive field work by one of us (ML) - involving visits to 165 sites throughout Hong Kong - showed that P. romeri has a relict distribution being confined to the islands of Lamma, Lantau and Po Toi in Hong Kong (Fig. 1). It does not occur on other islands or along the coast of southern China. A fourth island population on Chek Lap Kok (close to the northern coast of Lantau) was threatened by plans to construct a new international airport. That island was levelled in 1993, destroying all natural habitats and ruling out in situ protection of P. romeri. Extensive collections were made from Chek Lap Kok during 1992 in an attempt to rescue the frogs: 230 adults were obtained. Together with several clutches of eggs and tadpoles, they formed the basis of captive breeding populations maintained at the University of Hong Kong. Thirty adults were sent to Melbourne Zoo (Australia) so that a second breeding population could be established. The frogs survived well in captivity, and over 180 egg clutches were produced by the Hong Kong University population alone. The Melbourne Zoo programme was successful also, and a total of 706 captive-bred frogs were sent to Hong Kong.
Research funding from the Royal Hong Kong Jockey Club Charities Ltd allowed us to attempt the reintroduction of Philautus romeri to parts of Hong Kong from which it had been eliminated. Studies of the habitat of the frog revealed that it was a forest-floor species, that bred in unpolluted standing or slow-flowing waters. We do not know what caused the range restriction of P. romeri, but its restriction to island habitats was probably due to a combination of forest clearance plus habitat destruction and degradation (by pollution). In addition, P. romeri tadpoles and eggs are susceptible to predation by the introduced mosquito-fish (Gambusia affinis), and it is notable that this frog is only able to breed in places the fish has yet to colonise.
With the support of a number of organizations (Agriculture & Fisheries Department of Hong Kong Government, Kadoorie Farm & Botanic Garden, and The Hong Kong Zoological & Botanical Gardens), eight release sites which appeared to offer suitable conditions for Philautus romeri were identified: six on the mainland, and two on Hong Kong Island (see Fig. 1). A total of 1170 frogs and 1622 tadpoles was released in 1993 (at three sites) and 1994 (at eight sites). At least 90 individuals per site were introduced to provide an adequate founder population. Philautus romeri can breed in small water bodies, and thus some release sites were 'engineered' by the addition of suitable containers or the construction of small pools so as to provide fish-free habitat. Monitoring the success of reintroduction was carried out each year during the breeding season (when calling males can be detected and tadpoles provide evidence of reproduction). As of 1998, populations had been able to persist at 7 of the 8 release sites. Philautus romeri lives for approximately three years in the wild, but females are reproductively active for only two breeding seasons. The persistence of some of the re-introduced populations for 4-5 years is therefore indicative of successful establishment. However, the size of each population is small and only one has expanded its range significantly.
Philautus romeri are tiny and extremely cryptic. Annual monitoring at some sites failed to detect any animals in some years, even though visits in subsequent years revealed their continued presence. There is some evidence that interaction with other amphibians may limit the population size of adult P. romeri at release sites, since larger frogs of other species treat them as suitable food. This is the first time a breeding and release programme has been used to conserve a tropical frog, and the preliminary results indicate that the approach has promise.
First published in Reintroduction News, 17: April 1999
P.18-19
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