Hydrosaurus pustulatus (Eschscholtz 1829)

Little is known about the social behaviour of this lizard (5). Females breed once a year, but can lay several clutches of eggs in a good season (4) (5). Each clutch typically contains two to eight eggs and is buried in a shallow hole dug into the soil close to the waterside (4) (5). Hatchlings emerge after about two months (5) and are soon active and agile, enabling them to escape the numerous predators that may be lurking nearby, including snakes, birds and fish (4). Like their parents, hatchlings are good swimmers and will readily seek refuge in the water to escape approaching danger (4). The sail-fin lizard is omnivorous, feeding on a wide variety of plant material such as leaves, shoots, and fruit, and opportunistically supplementing its diet with the occasional insect or crustacean (4).

A European captive breeding programme has been set up by Chester Zoo (5), and efforts are now underway at three local rescue and breeding centres in Negros and Panay, Philippines, to establish local breeding, research and education projects based around sail-fin lizards (3). However, until the species, its distribution, abundance, and the threats it faces, have been more thoroughly investigated, it is extremely difficult to identify and act upon its conservation needs.

The sail-fin lizard is notable not only for its impressive size of up to a metre in length, but also for its rather spectacular appearance (3). Adults of this large mottled greenish-grey lizard boast a well-developed crest of tooth-like scales from the nape of the neck down the back (2) (4). However, the most distinctive feature of adult males is the erect 'sail' of skin at the base of their tail, up to 8 cm high, which provides propulsion for this strong swimmer to move through the water, and probably also plays an important role in territorial display and thermoregulation (2) (4). Another adaptation to its watery environment is the large, flattened toes that help the lizard to swim, and even enable it to 'run' across the water's surface, observed particularly in the lighter juveniles (5) (6).

Often called the 'sailfin water lizard' or 'sailfin water dragon', this semi-aquatic species is at home equally both in water and in trees (7). Its days are spent in vegetation overhanging unpolluted mountain streams of the Philippine islands' tropical rainforest, dropping into the water and swimming to the bottom at the first sign of danger, staying submerged for 15 minutes or more until they believe the coast is clear (4) (5) (7).

The sail-fin lizard is endemic to the Philippines, where it is found throughout the islands except Palawan (3) (7). However, the taxonomic status and relationships within and between different Hydrosaurus species in the Philippines remain highly debated and require clarification (3).

Classified as Data Deficient (DD) on the IUCN Red List 2006 (1).

Sadly, the enigmatic sail-fin lizard is threatened by ongoing habitat loss and degradation, in addition to hunting pressure, primarily for the pet trade (3). However, the species is classified as Data Deficient on the IUCN Red List 2006 (1) as little is as yet known of its status in the wild (5). Thus, more research is required before the real impact of these threats can be fully assessed.