A Story of Desert-Dragons and enchanted Princes of Sand: Reptiles and Amphibians in Goegap
By Tobias Feldt
As a faithful visitor of our homepage you certainly know that the striped mouse is the indisputable star in our field site and the central figure of our scientific desire. However, the Goegap Nature Reserve offers much more than “just mice”. Besides mammals, birds and insects there are also representatives of two already quite old taxonomic groups living here, not only just inside the reserve but sometimes also, very close to us, inside our research station: altogether 65 species of reptiles and amphibians are recorded or possibly occurring in Goegap. Some of them are hardly endangered but others can become very dangerous by themselves.
It is not surprising that there are so many different reptiles – altogether 61 species – occurring in this area because like no other animal group they are implicated to extremely dry and hostile habitats like the Succulent Karoo. Within this story for sure it is not possible to describe them all so let us then concentrate on some characteristic representatives.
In Goegap, snakes are certainly the type of reptiles which are attracting the most attention, at least if you are lucky enough to see them. For this reason there have already been a few FSM-Times-reports dealing with specific members of this group which shows the considerable interest people having in them, as well in a positive and negative way. And so questions like “Are there many snakes around here?” and “Has something ever happened?” are commonly asked by field assistants arriving at the research station for the first time. In fact, the reserve is home to some of the most poisonous African snakes which are well known for causing serious accidents all over the southern continent. But fortunately, incidents like these are hardly reported from Goegap and most of the visitors won´t even see a snake from a distance because they avoid humans whenever they can. Unfortunately, it is not the same with our mice which are a favoured prey for these reptiles and it is absolutely possible that, by doing radio tracking, you are following a snake, and not a mouse, but with a mouse inside.
The puff adder (Bitis lachesis) is one of the most dangerous snakes occurring in Goegap. Although its venom is weaker than that of the cobras and mambas it accounts for 60 % of serious snake bites in southern Africa due to its wide area of circulation and frequency. Besides, this thick and heavily built adder, which can grow between 1 and 1.5 m on average, is a comparatively sluggish snake. It does not crawl away in cases of trouble but relies on its perfect camouflage and usually issues a warning by giving a deep, hollow hiss which gave the snake its name. Anyway, people often step onto, or close to, puff adders and then get bitten. At dusk you can sometimes watch these as well diurnal as nocturnal reptiles lying on streets and roads to receive the last warm energy of the day.
Considerably more poisonous than the puff adder is the Cape cobra (Naja nivea) whose venom is as toxic as the black mamba´s. Without immediate treatment its bite can cause human death within an hour. Fortunately, encounters with this relatively small (1.5 m on average) and slender cobra are quite rare despite its wide area of circulation. And who is moving around attentively and thinking of some precautionary measures like wearing long trousers and sturdy shoes should absolutely not be worried about working in our field site.
The black spitting cobra (Naja nigricollis) is well known for the ability to eject its venom over a distance of about two meters making direct hits. There are only three other snakes in southern Africa doing so and some of them are even able to spit about four (!) meters. Growing up to 2 m this dark coloured cobra has an impressive appearance especially if – encountered and defending – it gets into a reared position while exposing its hood. In such a situation it is a blessing if you are wearing glasses.
Because of its dark colour and similar length, the mole snake (Pseudaspis cana) is often confused with black spitting cobras. But in contrast to them, this snake is harmless although large adults may inflict a painful bite while defending themselves. The mole snake spends most of its time underground searching for food. Here it pushes its way through soft sand using its pointed snout in search of rodents and – of course – moles.
While the snakes are shy and can hardly be spotted, the lizards appear much more conspicuous on the field site. Up to 34 species of skinks, lizards, agamas, chameleons and geckos may occur in Goegap and some of them are part of our daily life like the striped mice, bush Karoo rats and elephant shrews.
So are in particular the geckos which are famous for their ability to “stick” to seemingly smooth surfaces thanks to their unique toe-tips. These are covered with groups of scales with tiny hairs and by this amplify the attractive forces between the surface and the animal. From the beginning of spring numerous Bibron´s geckos (Pachydactylus bibronii) come close to our research station for foraging. When it is getting dark these normally nocturnal animals start sitting on walls, doors, windows and even underneath ceilings waiting for insects – especially moths – which are attracted by the inside lights. When the temperature rises more and more of them are showing up slowly “taking over” the research station. Through small chinks or short-time opened doors and windows they easily get inside the house so that in a sudden you have to share your room with a new roommate which from now on will enrich your sleep with its social interactive chirping sounds.
The Namaqua sand lizards (Pedioplanis namaquensis) are not as confiding as the geckos but unlike them they are omnipresent in the field site during daytime. Contrary to their name these slender and amazingly fast lizards which grow only up to 500 mm from the snout to the beginning of the long tail also occur in the Western Cape and parts of Namibia and Botswana. Sometimes it seems as if they are absolutely unable to stand still and in fact they are always ready for a little race against these strange big bipeds sometimes coming along the sandy paths. Like many lizards this species also has a colourful tail which it can shed when being attacked by a predator and which will grow again later on. Another remarkable characteristic you can usually watch them waving one of their forelegs, either to cool them down on the hot desert-sand or as a kind social interaction with their conspecifics.
There are also a few skinks living in Goegap at which the comparatively large western three-striped skink (Mabuya Occidentalis) certainly is one of the most conspicuous. Unlike most of the other skink species this bronze-coloured reptile with the three distinctive white stripes on the back still develops full legs and so looks more like a “real” lizard. Although it is normally feeding on insects it also seems to like the bait we are using to trap the mice. And so it sometimes happens that you don´t find a mouse or another rodent inside the trap but one of these scaled fellows, what a nice change!
But certainly the large southern rock agama (Agama atra) is the most beautiful reptile occurring in Goegap. Especially the breeding males – appearing in shiny blue with a bright stripe on the back – are very conspicuous and even attract attention in the colourful period of the wildflower display in spring. But also the females with their orange-yellow body and greenish-blue head are an optical pleasure. Thereby, both sexes are able to change their colour to improve their camouflage. This agama also shows an very interesting territorial behaviour: they maintain comparatively large territories inside which males and females form well-defined hierarchies so that there is always a dominant male and female. The dominant male usually perches on the highest point of his territory, push-up-like nodding his brightly coloured head as a signal for lesser males but also females. Looking at their size it is finally remarkable that the subspecies Agama atra knobelli which occurs in northern parts of Namaqualand and southern Namibia and grows up to 140 mm without the tail becomes noticeably larger in both sexes than its relatives which you can find throughout most parts of South Africa. Obviously, living inside a semi-desert like the Succulent Karoo is not as bad as it seems. By the way, there is a big disadvantage for agamas but also chameleons and monitors compared to other types of lizards because unlike them a tail which was once shed will never grow again.
The last group of reptiles you can find in Goegap are the tortoises. There are five species living here at which the Cape terrapin (Pelomedusa subrufa) is not yet recorded but may possibly occur in the nature reserve. Certainly the most well known is the leopard tortoise (Geochelone pardalis) but you should also not forget about the speckled padloper (Homopus signatus): measuring just 80 to 100 mm, this is the world´s smallest tortoise and endemic to the Namaqualand and northern parts of the Western Cape. However, it is not easy at all to spot a tortoise inside the nature reserve but sometimes you can see them on the road between Goegap and Springbok … hopefully still alive.
Not as common as reptiles are their herpetological relatives, the amphibians. This is not very surprising as their evolution is bounded to the few permanent or at least periodic waterholes and springs you can find in Goegap. For this reason there are only four species recorded or possibly occurring in this area, all of them belonging to the order Anura:
- platanna (Xenopus laevis),
- Karoo toad (Bufo gariepensis),
- Cape river frog (Afrana fuscilgula),
- Namaqua-caco (Cacosternum namaquense).
But even these few specialists which have become adapted to this hostile habitat during their evolution will hardly be seen in our field site which is way to dry for them to survive. But whoever is hiking through other parts of the reserve looking out for small pools or rills may have a good chance to spot a frog or a toad, either full-grown or still as a tadpole. By the way, so far it has never been reported if a “nice handled” desert-frog will transform into a prince or just into a small heap of sand.