Saturday, 16 April 2011

Frogs of Bristol 6: Handle with care

To wrap up this series on Bristol Zoo’s frog collection, there are the three poison arrow or poison dart frogs we currently have on show. Belonging to the Dendrobatidae, almost all the species of dendrobatid are highly colourful, day active frogs which tend to be fairly bold and therefore make good exhibits, unlike the tiny Mannophryne species I talked about last week. They can of course afford to be conspicuous, as their skin secretions are unusually toxic, although of the ones we have only the Golden Poison Frog, Phyllobates terribilis, is toxic enough to kill humans, with a single frog estimated on average having enough toxin to kill ten adult human beings or 22,000 mice. Fortunately, captive bred individuals never acquire the toxicity they have in the wild, as the wild diet appears essential for the production of the multiple toxins found naturally.

The other two species of dendrobatid we have on show, the Yellow-banded poison dart frog Dendrobates leucomelas and the Blue poison dart frog D. azureus are not sufficiently toxic to be used by local peoples in poison darts, being merely distasteful to predators. Despite all their defences however, there is at least one snake that specialises in poison dart frogs and other toxic amphibians, the 50cm Leimadophis epinephelus, which is so resistant it can even prey on Phyllobates species. Since it is so small however, it may only feed on juveniles of the more toxic amphibians it encounters.

The dendrobatid frogs all undertake various forms of parental care, with the species we keep all having egg clutches guarded by the male. When the tadpoles hatch after about 2 weeks they climb onto the male’s back and are transported from the nest site to small pools, bromeliads, or other tiny water bodies, where they mature in about 2 months.

The diet of dendrobatid frogs is composed of vast numbers of small insects, especially termites and ants. Some of the larger species will feed on woodlice, small millipedes, and insects up to the size of a small cricket, even small earthworms. The captive diet is mainly hatchling crickets and fruit flies, supplemented with wild caught small insects such as aphids and some wax moth larvae – although these last are very fattening and should not be fed frequently.

With their low reproductive rate and limited power of dispersal, dendrobatid frogs are very likely to produce unique local varieties. Wide ranging species usually are found in multiple morphs, all with restricted ranges. All of these are prone to extinction in the event of deforestation or chytrid fungus outbreaks, so there is considerable work being done on their preservation. They are widely kept by hobbyists, even the Phyllobates species (which is actually one of the easier to maintain forms). Naturally, anyone planning on keeping such a frog should do their research first, and this includes being able to produce sufficient food to maintain them – cultivating fruit flies is a vital skill for dendrobatid keepers. Hobbyists will often produce spectacular planted vivaria to house their animals, especially including ferns and miniature orchid species which do well in a dendrobatid vivarium – if the plants are growing and flowering well it is a good sign that the environment is correct for the frogs as well.

If the frogs do produce eggs, standard practise at Bristol is to remove the egg clutch and incubate them separately. Tadpoles must be reared singly, as many species are cannibalistic as larvae. At Bristol plastic drinking cups are used, with the water changed daily. The other important factor is exposure to UV light, which is vital to larval development. While the requirement for UV of reptiles is well known, amphibian requirements are less well studied, and probably vary greatly depending on the lifestyle of the species, with adults and larvae quite probably having different requirements.

This concludes this series on Bristol’s frogs. Next week, some new arrivals in the butterfly house and then a new series on our waterfowl.

(images from wikipedia)

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