Barn swallows - Mt Moreland – a haven for Frog Biodiversity   

By Jeanne Tarrant (African Amphibian Conservation Research Group) 

Background 

Amphibians are currently the most threatened group of animals on Earth, with at least one third (32%) of all known species (approximately 6300) threatened with extinction and 43% of species experiencing population declines. In comparison, 12% of birds and 23% of mammals are threatened. This is the biggest extinction event since that of the dinosaurs 65 million years ago. The causes of amphibian declines are many and varied – from obvious threats such as habitat destruction and pollution, to the more obscure threats of climate change and emerging infectious diseases, which together are creating the ‘perfect storm’ for extinction, with species disappearing even in relatively pristine habitats. In southern Africa, 15% of our 160 frog species fall into the top three Threatened categories (i.e. Critically Endangered, Endangered and Vulnerable). 

Amphibians play a key role as both predator and prey in the ecosystem and their disappearance will thus have far-reaching consequences for all other life on Earth. Furthermore, amphibians are important bio-indicators of the health of the environment, and the observed declines are a sure sign that something is fundamentally wrong with the global environment.  

 Mt Moreland’s frogs 

Conservation of habitat is the first step toward preserving frog biodiversity. The wetlands at Mt Moreland provide very important frog habitat, which hosts a wide variety of species, and is probably a refuge for many species that were historically widespread in the Durban area. At least 21 species are known from the area and three of these are listed as Threatened species according to the Atlas and Red Data Book of Frogs of South Africa, Lesotho and Swaziland. Preserving and maintaining the area in its current state is of crucial importance for the long-term survival of the frog community at Mt Moreland. The construction of the new La Mercy airport and associated infrastructure may pose a real threat to Mt Moreland’s frog population – especially at “Froggy Swamp” which is going to be the dumping ground for effluent from the airport site. Although the effluent will be treated prior to being released into the wetland it will still be introducing harmful contaminants from sewage, fuel and other pollution into the wetland. Frogs in general are very sensitive due to their semi-permeable skins to changes in the environment and contamination may affect egg and tadpole development and cause deformities and may make frogs more susceptible to disease. There is also the risk of untreated effluent being released in the event of power failures or if capacity is exceeded – both probable scenarios.

Other threats from the airport include direct deaths of frogs caused by increased traffic in the area, loss of habitat as a result of both the airport itself and any concomitant construction and disruption of calling during the breeding season due to air traffic noise. Although the long-term goal is the re-zone both Lake Victoria and Froggy Swamp as a conservation area it is still very likely that these habitats will face detrimental changes as a result of the airport being in the vicinity. 

The three Threatened species at Mount Moreland are the Pickergill’s Reed Frog (Endangered), the Natal Leaf-Folding Frog and the Spotted Shovel-nosed Frog (both Vulnerable). Pickersgill’s Reed Frog is particularly important as it occurs only at 10 isolated sites along the KZN coastline between St Lucia and Kingsburgh, with Mt Moreland hosting one of the biggest known populations of this species. This small frog favours dense reed beds and, even if present, is difficult to find and little is known about its life history. A student from North-West University will be monitoring this species at Mt Moreland over the next year, both to learn more about the species and to note any changes in population size that may be a result of negative impacts from the airport.

The Natal Leaf-Folding Frog is comprised of two sub-species, A. s. spinifrons, which occurs at low altitudes of the Eastern Cape coast and A. s. intermedius, which occurs at altitudes above 1000m in Kwa-Zulu Natal. Within this range populations are fragmented and numbers appear to be in decline. Populations of A. spinifrons have been reduced as a result of habitat loss, habitat fragmentation and the introduction of alien plants. At Mt Moreland the coastal subspecies occurs at various sites within the area. The Spotted Shovel-nosed Frog is distributed along the northern Kwa-Zulu Natal coastline as well as at a few inland points in southern Mpumalanga. Its fossoria l(underground) life style makes this an interesting species, but also very difficult to find. It has been heard calling at various locations around Mt Moreland. Its habitat is also being subjected to high levels of urbanisation and agricultural activities, especially on the coast.

It is thus essential that Mt Moreland is recognised for its importance in the Durban area as a sanctuary for a vast array of animal life, least of which are the frogs, and that all is done to preserve this natural heritage.