Saturday, 9 April 2011

Frogs of Bristol 5: Noisy but secretive

One of the least conspicuous, but noisiest, of all the frogs we have at Bristol are our Trinidad Stream Frogs, Mannophryne trinitatis. Originally thought to be found on Trinidad in the Caribbean and part of the mainland of Venezuala, the mainland population is now classed as a separate species, M.venezuelensis. This is only to be expected, as any interchange between Caribbean islands and South America must be very infrequent at best. Our species is part of a group of very similar species mostly found in montane forests of Caribbean islands and Venezuela. Several are listed by the IUCN as declining, near threatened, critically endangered, or at best data deficient, with the Trinidad Stream Frog classed as Vulnerable. At present, they are still reasonably common in suitable habitat.

Part of the reason for the lack of knowledge of the various forms is their small size. Trinidad Stream frogs are at best under 2cm long, usually smaller, and are cryptically coloured, unlike their better known and more colourful relatives the poison dart frogs. They are animals of leaf litter, where they lay their eggs. As with poison dart frogs, the eggs are guarded by the male, and the newly hatched tadpoles are carried by the male to small pools, chosen for their lack of predators.

The best way to locate these frogs is by ear. The males are amazingly loud for their size, presumably so they can be heard above the noise of the streams and waterfalls they live beside. The effectiveness of this can easily be discovered in the reptile house, where we have a group living free in the house. The reptile house has a 12m high waterfall falling onto rocks over the pools housing our turtles and dwarf crocodiles, and the splash zone creates a perfect replica of the streams and waterfalls they live beside in the wild. Males tend to call from prominent rocks near the waterfall, but visitors are only likely to see them if they move, as they are the same colour as the rocks. This is doubtless very useful camouflage, as they do not have the same level of toxins as the poison dart frogs and could be eaten by practically anything. Aside from being inconspicuous, their only defence is that they are amazing jumpers, hence their other English name of Rocket Frog.

Their own diet is what one would expect – minute insects and other leaf litter invertebrates. At Bristol the ones kept in vivaria are fed pinhead crickets, fruit flies, and springtails, with tadpoles fed on flaked fish food and some other artificial diets. As with all amphibians, they are prone to heat stress, so it is important that they are not kept too warm. Lighting requires a low level UV bulb – too much UV can be a cause of cataracts in animals not used to living in full sunlight, and these frogs favour shady streams.

Unlike the poison dart frogs, which are very colourful and showy animals and make for a good display in a collection, Trinidad Stream Frogs are rarely seen in zoos. At present ISIS only lists 99 individuals, all in the UK. This kind of bias is a major problem for conservation Рzoos need animals which are visually interesting fro visitors to want to come and see, whereas a lot of vulnerable or endangered creatures are frankly dull to look at unless you are a specialist in the group they belong to, so they tend not to get the attention and conservation funding they need. The IUCN red list has 9 species of Mannophryne which are classed as Endangered or Critically Endangered, but only one organization is involved in their conservation, the Laboratorio de Biogeografía/ Biogeographic Laboratory, Universidad de los Andes in Venezuala. I am not aware of any projects targeted directly on the Caribbean species.

Next week, some true poison dart frogs – colourful character with complicated lifecycles.

(image from Amphibiaweb. Picture by Dr Joanna M Smith)

1 comment:

  1. They roam free in the reptile house? That's cool!