Saturday, 2 May 2015

Lizards 10: Panther Chameleon

Female Panther Chameleon
Of all the world’s lizards, chameleons are perhaps the most instantly recognizable. The distinctive eyes, which are extremely sharp – chameleons probably have some of the best vision of all reptiles – can either give good vision in any direction or be focussed on the same target to give stereoscopic vision and depth perception, essential when using their other distinctive feature, the extensible tongue (which can be as long as their bodies), to catch their prey.

The other feature chameleons are famous for is of course their colour changing ability. This is the result of a double layer of pigment cells in the skin. The upper layer contains cells with a lattice of guanine crystals. Changes in the lattice structure result in changes in the colour of the reflected light from blue through to red wavelengths, and this combined with yellow pigment granules results in shades of green. The deeper layer changes infrared reflectivity, and is used in thermoregulation.

It is widely believed that chameleons change colour to match their surroundings. This is in fact not true, chameleons have an inbuilt set of colour patterns, different for each species, and switch between them depending on environmental cues such as humidity and light levels, and their own internal state – for example gravid females have a distinctive colour pattern to ward off unwelcome attentions from males, and courting or fighting males will display especially vivid colour patterns.

All chameleons are predators, and most feed of insects of various sizes depending on the size of the animal. The largest chameleons will take smaller lizards, frogs or even birds. They hunt by stalking their prey like a big cat, hence their name (“chameleon” is derived from the Greek for “little lion”). They rely on the camouflage and stealthy movement to get within range, and their extensible tongue means that they can catch prey while their target still thinks it is safe even if they are spotted. They have a high metabolic rate, and healthy chameleons have good appetites for anything that moves and appears edible. Occasionally, some species will also feed on foliage or fruit, but this is not a major dietary component.

Chameleons are solitary by nature, and males especially are quite territorial, especially in the breeding season. Except in large enclosures, they are therefore best kept singly or in pairs, with plenty of branches to climb on and space themselves out. They can be cannibalistic, and for this reason hatchlings in particular tend to avoid areas where adults typically are found.

Various species of chameleon are confined to the old world, in particular Africa and Madagascar. There are a few outside this range in Europe and India, and there may have been more in warmer periods of earth’s history, as fossils have been found as far north as Germany. Today as a result of the pet trade there are introduced populations in many parts of the world, most significantly Hawai’i although there at least one species is also known to have a small population in Florida.

At Bristol three species are on show at present, with the largest species being a female Panther Chameleon, Furcifer pardalis. This species originates from Madagascar, where at least half the world’s chamleons are currently found. It is listed as Least Concern by the IUCN, and is found in northern and eastern Madagascar in forested areas. There is considerable variation in colour between males from different areas, with the different forms varying from mainly blue ground colour to mainly red or orange. They tend to be ornamented, especially when displaying, with various contrasting stripes. As this species is one of the most commonly kept pet chameleons, there is a risk that localised colour forms may be threatened by collection for the pet trade. On the other hand, they seem to be able to thrive in disturbed forest habitat, and abandoned farmland or regenerating scrub may actually increase the available habitat and therefore population numbers.

Panther chameleons are one of the largest chameleons, with large males reaching 45cm. Females, like the one on show at Bristol, are about half this size. They can lay 1 or 2 dozen eggs in a clutch, which are laid in a burrow dug by the female during the rainy season and take around 8 months to hatch. This is quite a long time for a tropical reptile, but lengthy incubation periods seem to be fairly typical for chameleons. The newly hatched young grow rapidly and are mature by the next breeding season. Chameleons are short lived, especially females, and even in captivity males seldom reach five years. In the wild a typical lifespan is probably no more than one or two years as a result of predation – despite their camouflage there are many natural enemies such as birds of prey, snakes, and predatory mammals.

(images are mine)

No comments:

Post a Comment