Tuesday, 19 November 2013

Snakes 2: Mangrove Snake

The other venomous snake that we have on show at Bristol is the first snake encountered as you enter the Reptile House, a fine specimen of the Mangrove or Gold-Ringed Cat Snake, Boiga dendrophila. Despite their English name, Mangrove snakes are more commonly found in lowland rain forest than in actual mangroves, but they certainly deserve their specific name, as they are highly arboreal. Unlike the rattlesnakes and cobras, they are classed as opisthoglyphous (“back-fanged” in common usage), as although they have venom instead of specialised fangs to inject it at the front of their mouths, They have up to 3 enlarged teeth further back in their mouths, and rely on chewing to introduce venom to their prey. Opisthoglyphous snakes are usually less venomous to humans, and for Mangrove snakes no human fatalities have been reported, but some people have more extreme reactions than others and snakes from different parts of their huge range in South East Asia probably vary in toxicity, so it is unwise to handle them without protection.

Mangrove snakes are just one of around 30 Boiga species found in a variety of habitats from South East Asia west to Sri Lanka and north into Iran. Perhaps the most infamous of the group is the Brown Tree Snake, a highly invasive species on Pacific Islands which has been the cause of numerous bird extinctions on islands where it has been introduced.
Brown Tree Snake, Guam

The various Boiga species are nocturnal, and have slit pupils which enable them to see in low light levels when they are active. These resemble the eyes of cats, hence the common name of Cat Snake for the various species. They seem to be generalist predators, feeding on lizards, amphibians, roosting birds, and rodents as opportunity arises. The Mangrove Snake is one of the largest species, with some individuals exceeding 2.5m in some parts of their range.

Mangrove snakes lay eggs, with up to 15 in a clutch in the case of large females. Eggs take 90 – 120 days to hatch, and the hatchlings are around 30cm when born. In captivity, they require large quarters with plenty of branches for climbing, and a humidity of around 80%. Temperatures around 28C are suitable. They seem to feed best after dark, which is when they would be hunting for food in the wild. During the day they tend to remain immobile most of the time, often curled up on a branch. In captivity the staple diet is rodents of a suitable size, with youngsters taking pinkies at birth. Neonates may sometimes need their food to be scented with a lizard, as that is most likely what the newly hatched individuals mostly feed on in the wild.

With their varied diets and large distributions, most of the Boiga species are classed as Least Concern by the IUCN, although some of the endemic island species in particular may be threatened by deforestation. The IUCN Red List has only one species classed as Endangered, Bourret’s Cat Snake B. bourreti, which is known only from three locations in central Vietnam, although its range is probably wider. Several other species are classed as Data Deficient, as these snakes are hard to study in their natural habitat.

(Photo from Bristol zoo taken by myself, wikipedia)

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