Zandvlei Trust

Frogs of the Zandvlei Area

If the rain and cold are not clear enough signs that winter has finally returned, then the nightly frog choruses are a dead give away. Frogs are conspicuously vocal animals. Frog calls or specific mate recognition systems (SMRS) - what the experts call frog calls - are mainly used to attract a mate. Sound is the best form of communication for nocturnal animals which live in thick reeds or vegetation. Each specie has a distinctive male advertisement call and female response call. These calls are often the only evidence that there are frogs in the area and provide a valuable tool for identifying them. I have only recorded four different species of frog in and around Zandvlei. This is due mainly to the fact that few frogs are able to tolerate the saline waters of Zandvlei. Frogs are very good indicators of ecosystem health as they have the ability to absorb oxygen through their skin! This form of respiration causes frogs to be vulnerable to chemical pollutants. Frogs are therefore unable to persist in highly polluted systems.

Food chain
Frogs and their tadpoles are a valuable link in the food chain. They are eaten by birds, snakes, otters, water mongoose and other frogs. Frogs are valuable pest control agents and consume large amounts of insects and spiders. They are unselective feeders and highly opportunistic, feeding on whatever prey is abundant. It is interesting to note that frogs do not drink but absorb water through their skin.

The most commonly heard and seen frog around Zandvlei is the Clicking stream frog. This little frog is the one most frequently found in gardens, often far from water. The eggs are often laid on the damp ground where the tadpoles develop quickly. The clicking stream frog is usually about 35mm in length and is found through out the western Cape. The coloration of these little frogs is highly variable and are best identified by an almost total lack of webbing on their toes. The call is described as a wooden tapping sound emitted with monotonous regularity.

By far the most impressive and threatened frog in our area is the Leopard toad. The leopard toads found on the Cape Flats have recently been recognised as being distinct from the other populations in the rest of South Africa. The range of this species has been severely reduced through urban sprawl. The frogs need large areas away from water in which to forage and are often killed by cars at night. The healthy population of leopard toads at Zandvlei is of great importance and needs to be actively protected. They can obtain a large size and big specimens can quite easily fill the palm of a man's hand. Leopard toads are readily identified by their bright colouration, large size and the presence of two large glands on their upper back. These glands contain a toxin which is used to deter predators. The glands have no effect on people handling the toads but they should not be eaten!

The call is a deep snore of a second in duration and is heard in spring.

The Cape sand frog requires open sandy areas and is not often found in gardens. They seldom attain more than 45 mm in length and can be identified by their pale grey to brown toad like appearance The Cape sand frog spends a large portion of its time underground and can burrow rapidly. The call of this frog is distinctive and comprises of distinct ringing notes of about 7 per second. The attractive call is mostly heard in early summer.

The Cape river frog is not fond of saline waters and is most frequent in the Westlake Wetland area. These frogs are easily identified by their large size and totally webbed feet. They grow fairly large and can attain over 80 mm. Cape river frogs will eat anything that will fit in their mouths, including smaller Cape river frogs. They feed by sitting motionless on the edge of the water and give away their presence with a loud splash if disturbed. The short groan like call is emitted irregularly and usually from the surface of deep water.

Warts?
Frogs are incredibly interesting creatures which are an intricate part of the ecosystem. Many old fallacies concerning frogs and toads (most of which include warts!) are still considered fact by many people. Such fallacies are fortunately becoming less common and the valuable role of frogs is being recognised.

Many other, more cryptic species undoubtedly still occur in the area so please keep a look out and pass on any interesting sightings to me.

August Toads
In case you don't know, the cacophany of
frog calls that have suddenly erupted from the vlei is from August Toads, so named because that's when they call, also known as Snoring Toads because of the sound they make. Most people know them as Leopard Toads because of their colouring. They live here all year round, but this is spring, time to mate, so it pays to advertise Come on ladies, come to me, come to me, I'm a great noise-maker, big chest, powerful gular sacs  and what a lover! The Fish Eagles are also calling. Two adults and a juvenile have been seen flying over the vlei. They, too, are a sign of spring. Carp are coming into the Zandvlei to breed, so the Fish Eagle arrive to greet them. 
 

Clifford Dorse

   

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