Colours of Wildlife: Rain Frogs

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Willem is a wildlife artist based in South Africa. He says "My aim is simply to express the beauty and wonder that is in Nature, and to heighten people's appreciation of plants, animals and the wilderness. Not everything I paint is African! Though I've never been there, I'm also fascinated by Asia and I've done paintings of Asian rhinos and birds as well. I may in future do some of European, Australian and American species too. I'm fascinated by wild things from all over the world! I mainly paint in watercolours ... but actually many media including 'digital' paintings with the computer!"

Colours of Wildlife: Rain Frogs

Here are some pictures to start things off:

This is a Bushveld Rain Frog, scientific name Breviceps adspersus. Here is a photo of a little one we found on the porch a few days ago. Here's another.

Rain frogs are very unusual frogs in numerous respects! First of all there's their shape. They are very, very round! Their heads are very small (in fact, Breviceps means 'Short Head') and hardly protrude from their round torsos. And neither do their legs – both front and hind legs are very short. Consequently, rain frogs can't hop or jump ... and neither can they swim! Over here when it's raining we go out and check if any have fallen in the swimming pool ... we have to rescue them if they do, else they drown.

Their name comes from their habit of only being active when it rains. The rest of the time they are buried underground ... they spend absolutely the majority of their lives buried like this. Their toes are not webbed for swimming, but they have *some* webbing between the hind toes, as well as a hard ridge on the heel. This makes their feet 'shovel-like' to help them with digging. They dig by shovelling the soil backwards with the hind legs, and then 'reversing' their bodies into the hole.

Rain frogs dig these holes – usually rather shallow – in the soil. They are sometimes come across when gardening – they will 'scream', with a high-pitched whistle, when they are disturbed. Over here I always try and garden gently in case I come upon one of them.

In South Africa, in most places the rain season starts in late spring or early summer. Drenching rain at this time will stir the little frogs into action. They will emerge, go and feed (mostly feeding on termites, especially the winged 'alates' that also emerge during times of good rains) and call to each other. Their calling is characteristic of summer and spring when the rains are falling. It's almost impossible to describe ... it's not quacking in the slightest, its almost insect-like chirping/buzzing.

The calling is because there's another important task that needs to get done during the wet season: mating! There will be many males in any typical garden, calling, and the females honing in on the one whose call she likes best. Female rain frogs are much bigger than the males. Copulation ... actually, 'amplexus', since these frogs fertilise each other externally rather than internally ... is also different from other frogs. While in other frogs, the male 'embraces' the female and clasps her with his forelegs under her armpits, this is impossible for these round, short-limbed frogs. Instead, the male literally glues itself to the back of the female! It's a strong adhesive to the extent that you should never try to separate two frogs that you find like this – it might result in their skins being torn!

So, the little male glues itself to the back of the big female and she carries him round like that for quite a while until she's ready to lay her eggs. This, too, happens in a hole dug in the ground – in this case rather deep, up to 40 cm/16 inches below the surface. The female lays her eggs, and the male secretes sperm over them. Then the female secretes a solvent that dissolves the glue holding her man on her back – and he can leave! The eggs are buried; they hatch there – unlike other frogs, rain frogs don't have a typical tadpole stage. The tadpole stage remains inside the egg – they turn into little frogs and *then* do they hatch.

The above describes the Bushveld Rain Frog. But there are many other rain frog species! As far as I know, most (if not quite all) of them are restricted to South Africa. All of them are instantly recognisable as being rain frogs – by their shape alone. But ecologically, they inhabit lots of different habitats.

At the one extreme is the Desert Rain Frog, inhabiting one of the driest deserts in the world, the Namib – along the coast of Namibia and a small part of South Africa. Here, the frog remains buried in the sand for great periods, making use of moisture from seafog-dew, and infrequent rain showers. This species also has remarkable skin on its belly. The skin is very thin and translucent, with blood vessels visible through it. The frog can absorb moisture rapidly from the sand, through this thin, vascularised skin. This remarkable little desert frog is currently threatened by diamond mining in its sand dune habitat. (The Namibian coast is one of the richest sources of diamonds in the world.)

From there, rain frogs are found in semi-desert, coastal scrub, 'fynbos' (similar to Mediterranean shrubland), savannah, grassland, and also true forest. One species is found on the rugged fold mountains of the southwestern Cape. Most species are found in forest, where they dig themselves into the leaf-litter and humus. In these moist environments they can be much more active than in drier savannah, grassland or desert, and consequently, they can also breed more regularly and evolve faster. One of the prettiest little rain frogs is the Strawberry Rain Frog of forests of the southern Cape. It is reddish or pinkish with black 'granules' (small warts) on its back, and plum-coloured with white spots on its belly.

New species of rain frogs are still being discovered. A great tool in discovering new frog species is the tape recorder! The way to do it is to go to a place where you expect rain frogs would be, with your trusty tape recorder in hand, and then record their calls. Go back to your lab or whatever, and then compare the recordings with those of known rain frog species. Differences in call, in frogs, generally correspond to genetic differences ... because frogs generally use their calls to identify themselves and recognise members of their own species. Rain frog calls are quite diverse, ranging from whistles, to plaintive moans, to the chirping or buzzing sounds of the bushveld rain frogs and their relatives.

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