Saturday, 28 March 2015

Lizards 5: Solomon Islands Skink

Adult Corucia with juvenile
One of the more unusual, as well as larger, lizards on show at Bristol is a family group of the Solomon Islands Skink Corucia zebrata. Unfortunately, members of the public all too often walk by their enclosure as they tend to be secretive and immobile during visiting hours, often inside hollow cork tubes or resting on an overhead beam in their enclosure. This is a loss for the visitors, as they have one of the more complicated social structures and lifestyles of all lizards.

Physically, Corucia’s are large skinks, weighing up to 1kg and being about the same size as an adult Blue-Tongue Skink Tiliqua spp, to which they are actually fairly closely related. Tiliqua skinks are however terrestrial lizards of Australia and New Guinea, whereas the Corucias are found in the various islands of the Solomon group in the south west Pacific. Currently there are two described subspecies, but reports of lack of successful captive reproduction in individuals with parents from separate islands in may indicate that actually C.zebrata is a species complex with multiple cryptic species. All are a mottled green, with long, prehensile tails, which give them more agility as they climb through their home trees. Total length is around 60cm, of which half is tail.

In the wild, they tend to hide away during the day, emerging at dusk, and to a lesser extent dawn, to feed on foliage of various trees and vines, as well as flowers and some fruit. They have powerful crushing teeth, and there are reports of captive individuals feeding readily on snails, so they probably do the same in the wild. Other potential animal prey they would have access to are birds eggs, caterpillars and other insects, but the bulk of their diet is certainly vegetarian. Telemetry studies on wild individuals have shown them staying in the canopy of a single tree, usually a strangler fig Ficus spp.
A juvenile Corucia
The most interesting feature of Corucia are their highly unusual social and reproductive behaviour, which is mammal-like in its complexity. Skinks live in reproductive groups of a male, one or more adult females, plus juveniles of various ages. Members of the group will often share a hiding place, usually a hole in the trunk or branch of one of their home trees, and they will all defend their site. Females are live bearers like many skinks, but in Corucia reproduction has advanced to the point where there is a true placenta providing nourishment to the developing embryo. Usually only a single young is born, after a pregnancy of 8-10 months, but twins or even triplets are not unknown. Maternal care extends even after birth, with newborns remaining in the family group, and even riding around on their mothers’ backs. Babies are known to eat the faeces of the adults, probably to obtain the bacteria necessary for proper digestion of their vegetarian diet. This has implications for veterinary care of captive animals, as antibiotic treatment may affect or even eliminate natural gut bacteria, with damaging effects on treated animals even if the original condition is cured. In at least one case reported, a decline in condition in such a treated animal was resolved following feeding it mealworms which had been smeared in the faeces of the other adult animals in the enclosure. It is quite possible that other vegetarian reptiles may have similar issues after antibiotic or other drug treatment.

The current status of Corucia in the wild has not been assessed by the IUCN. They were collected and exported for the pet trade in the past, but they have now protected status, and the main threat is probably deforestation. Given the possible population structure in the different islands, it would be very desirable that all captive breeding only takes place between individuals that can be traced back to particular islands, and certainly not between the two described subspecies.

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