Written by Zoë C Poulsen. Photos by Gigi Laidler, Fayrus Prins, ‘ryanderoo’, Oliver Angus, Kobus Lubbe and Paul Bester (www.inaturalist.org)
On rainy nights in Cape Town, our wetlands are filled with the calls of many different frogs. As a newly recognized Ramsar city with an extraordinary diversity of wetland habitats, Cape Town is home to a high diversity of amphibians, which live in our urban national parks, nature reserves, gardens, and community spaces.
So, which frog species live in the City of Cape Town? Where do they live? Why are they important? How can we help to conserve them? In this edition of FynbosLIFE’s HabiCHAT blog, we learn more about the secret life of Cape Town’s frogs.
Frogs are small vertebrates that need water or a moist environment to survive. Taxonomically, they are part of the amphibian class along with newts and salamanders, from which they differ by the adults not having tails.
Both frogs and toads belong to the order Anura, which is the only amphibian order that occurs in Southern Africa. This is the largest order of amphibians, comprising more than 6 700 worldwide.
In Southern Africa, toads are one of the frog families and, therefore, are classified as frogs along with, for example, the rain frog family and ghost frog family.
There are 13 different frog families found in Southern Africa that are divided into 34 different genera and 169 species. This means that scientists have conducted DNA analyses to determine how the different species are related and what common ancestors they have.
Once they have been scientifically described from a type specimen, which is usually an individual or a few representative individuals from a species, each species is assigned a scientific name. The same name is then used by scientists worldwide in reference to that specific species.
Although the far southwest of the Western Cape has a relatively low diversity of amphibians compared with areas of South Africa with a warmer and more humid climate further northeast, it has a far higher proportion of endemic frog species, with endemicity increasing in a southwesterly direction across the country.
An endemic species is defined as one that is only found in a specific geographic area and nowhere else in the world. A species may be endemic to a specific country, region, or even a wetland or mountain stream.
A key example of this is the microfrog (𝘔𝘪𝘤𝘳𝘰𝘣𝘢𝘵𝘳𝘢𝘤𝘩𝘦𝘭𝘭𝘢 𝘤𝘢𝘱𝘦𝘯𝘴𝘪𝘴), which has been so named because it reaches no more than 18 mm in length and is one of the world’s smallest frogs.
The microfrog is only known from an area of less than 10 km2 in the southwestern Cape lowlands on opposite sides of False Bay from the Cape Flats to the Agulhas Plain. With most of its former habitat lost to urbanisation, it is found in undisturbed lowland pools and vleis with slightly acidic water in fynbos habitats. It is classified as Critically Endangered on the Red List.
The Table Mountain ghost frog (𝘏𝘦𝘭𝘦𝘰𝘱𝘩𝘺𝘳𝘯𝘦 𝘳𝘰𝘴𝘦𝘪) is a highly secretive frog species that is endemic to a few fast-flowing streams in gorges in afrotemperate forest on the eastern and southern slopes of Table Mountain.
There are six different species of ghost frog found in different parts of South Africa, but the Table Mountain ghost frog is recognised as being a different species by the lack of a distinct horizontal stripe through the eye.
The ghost frogs are named after the type locality of the Table Mountain ghost frog, Skeleton Gorge, which is located on the eastern slopes of Table Mountain above Kirstenbosch National Botanical Gardens. To this day, nobody knows who the skeleton of Skeleton Gorge was named after.
Given that frogs do not drink water, they need moisture to survive, which they absorb through their skin through a process known as osmosis while they are in the water or on wet surfaces.
Therefore, frogs primarily live in habitats with high levels of moisture availability, with different species living in different ecological niches.
Some frog species such as the Cape sand frog (𝘛𝘰𝘮𝘰𝘱𝘵𝘦𝘳𝘯𝘢 𝘥𝘦𝘭𝘢𝘭𝘢𝘯𝘥𝘪𝘪) live in wetland systems that are fed by rainwater, which are neither fed by nor drained by any watercourse. These include pans, pools and ponds, many of which are seasonally inundated.
Other frog species, such as the clicking stream frog (𝘚𝘵𝘳𝘰𝘯𝘨𝘺𝘭𝘰𝘱𝘶𝘴 𝘨𝘳𝘢𝘺𝘪𝘪) live in riverine systems, which may include permanent and seasonally ephemeral rivers, temporary streams, perennial streams and dry riverbeds.
Marshland systems including vleis and hillslope seepages from perched wetlands are also home to a range of frog species. Cape Town’s vleis represent a vital breeding ground for the Endangered western leopard toad (𝘚𝘤𝘭𝘦𝘳𝘰𝘱𝘩𝘳𝘺𝘴 𝘱𝘢𝘯𝘵𝘩𝘦𝘳𝘪𝘯𝘢) and the Critically Endangered Rose’s mountain toadlet (𝘊𝘢𝘱𝘦𝘯𝘴𝘪𝘣𝘶𝘧𝘰 𝘳𝘰𝘴𝘦𝘪).
Some of Cape Town’s frog species dwell in terrestrial habitats, where they live in loose sand, leaf litter on the forest floor, rocky outcrops, open fynbos, renosterveld and strandveld, as well as in domestic gardens. Perhaps one of the most well-known examples of this is the Cape rain frog (𝘉𝘳𝘦𝘷𝘪𝘤𝘦𝘱𝘴 𝘨𝘪𝘣𝘣𝘰𝘴𝘶𝘴) that is a common garden resident in Cape Town.
With frogs facing a range of threats on a global scale, more than half of the world’s frog species are now classified as threatened with extinction. Frogs are now the most threatened vertebrate group in the world.
Given the complex and integral role that frogs play in our wetland and terrestrial ecosystems, the ecological effects of ongoing frog species extinctions are likely to be far-reaching.
With the ongoing transformation of wetland habitats for urban expansion and agriculture, habitat loss is one of the main threats facing amphibians worldwide. Human-driven climate change, disease outbreaks and environmental pollution are further accelerating population decline.
Given their sensitivity to habitat changes and degradation such as environmental pollution, frogs are truly the ‘canary in the coal mine’ as indicators of environmental health.
This means that the ecological impact on amphibians becomes apparent before other groups such as plants, mammals or birds respond to the effects of environmental degradation.
So, what can we do to help Cape Town’s threatened frog species? One of the most important ways that we can help is to be the eyes and ears of scientists looking to monitor the threat status of our local amphibians through population changes.
As citizen scientists, we can look out for frogs in our local nature reserves, gardens and community spaces and document them using the citizen science data collection platform iNaturalist. Scientists can then use this data to assess population change over time.
Particularly during winter and early spring in wet weather, look out for frogs crossing the road and drive carefully to avoid squashing them as they move through our neighbourhoods to their breeding sites.
If you live in an area where the Endangered western leopard toad occurs, consider joining your local western leopard toad conservation group and help the toads during the breeding season by moving them across busy roads, while helping to collect valuable population data for scientific research.
With the accelerating loss of natural habitat in urban areas, domestic, community, and school gardens and other outdoor spaces such as parks are becoming increasingly important for wildlife such as frogs.
There is a range of ways that you can help to make your garden or outdoor space more frog friendly. First, find out which frog species occur in your area, and what their preferred habitats are.
With this information, you can then create areas of habitat in your garden for your locally indigenous frogs. You may want to consider building a pond or providing shallow containers filled with water.
Dense planting helps to provide shelter for frogs and other wildlife, particularly with locally indigenous plants found in your area and local veld type. It is also important to avoid the use of chemicals such as herbicides and pesticides in cultivating a wildlife-friendly garden.
At FynbosLIFE we only recommend planting suitable habitats to welcome frogs back into your garden, but strongly advise against moving tadpoles or adult frogs away from their original location. Sadly, the risk of disease, hybridisation and potential new species invasions could end up doing far more harm than good.
If you would like more information on selecting and purchasing the right plants to grow a frog-friendly garden, then please consult our friendly staff when visiting our retail nursery for further guidance on the best plant choices for your area of Cape Town.
Du Preez, L. Carruthers, V (2017) Frogs of Southern Africa: A Complete Guide, Struik Nature, Cape Town, South Africa