By Ronan CarvillÂ
Frogs are an often overlooked and undervalued category of biodiversity, but with the visit of the leading Anuran (frog and toad) scientist in Southern Africa, Dr Jeanne Tarrant, they became the centre of attention. The Diploma students got a week-long crash course in all things froggy.Â
Frogs tend to have a slightly negative reputation in traditional culture and mythology, from the plague of frogs in the Bible to African grandmothers’ tales of frogs shooting lightning from their mouths or causing the rain! Additionally, many of the students had an initial level of disgust for the slimy and odd nature of frogs. However, the activities over the week created a burgeoning curiosity that completely eclipsed and extinguished this fear. Indeed, students were so fascinated that they will be doing their required biology project on frogs.Â
The week started with an overview of amphibians. There are actually three orders of amphibians, of which the Anura (frogs) are only one. The others are the Caudata (salamanders) and the Gymnophiona (caecilians). The Caudata include the newts and the alien-looking axolotl, and the cave-living eyeless olm. However, South Africa has only anurans. Did you know that toads are a subset of frogs, so all toads are frogs, but not all frogs are toads?Â
One defining feature is that they need moisture to survive, but there is significant breadth in the level of moisture required and how they obtain it. We often think of frogs as needing to be almost always in a body of water and only coming out when it rains. However, while indeed there are species which are like this, there are also species like the desert rain frog in southern Namibia that are never in standing water and never swim. It survives by absorbing desert rain fog and buries itself in sand dunes during the day.Â
Speaking of burying, many frog species bury themselves in moist mud or soil to keep themselves safe and wet. Some are hind limb diggers, in that they dig their tunnel facing outwards and slowly back in, while some use their forelimbs or even their head. The shovel-nose frog uses a specially adapted nose/head to dig.Â
We all know of the fascinating stages of metamorphosis that frogs go through throughout their lifecycle — from eggs to tadpole to froglet to fully grown adult. I learned that the stage from tadpole to frog differs greatly from species to species. In species that do not have much time or permanent water, this phase can take as little as a few weeks, while species that have more permanent water can take as long as two years.Â
South Africa is a hotspot for Anuran biodiversity, with a total of 135–150 species, with over 50% being endemic. Unfortunately, frogs are uniquely threatened, with the highest levels of extinction and threat of any order of vertebrates. Part of this is due to their sensitivity. Their skin is highly sensitive and permeable, and they also breathe through it, so they are particularly vulnerable to pollution. As freshwater habitats accumulate pollution from agriculture and industry, the impact is amplified. Sedimentation from erosion, often caused by human activity, is also a pollution threat.Â
Another major threat highlighted was invasive species. Many invasive plant species can completely disrupt the balance of freshwater habitats, impacting frogs. Habitat destruction is also devastating, particularly the draining of wetlands, which is widespread across the country. Many habitats in KwaZulu-Natal along the coast have been lost or are under threat from development. Indeed, Dr Tarrant works mostly in highly human-disturbed areas and not in wildlife areas like Kruger.Â
Surveying for frogs can be a tricky business. While direct encounter sampling (i.e. getting muddy and wet and searching by hand to capture some) is used, the most effective method is Passive Acoustic Monitoring (PAM). Just like birds, frogs sing to attract mates and defend their territories. It is only the male that sings, croaks or ribbits. Each species has a distinctive sound, which can vary from high-pitched squeaks to booming croaks. One of them even sounds like bubbles popping. While we can appreciate the dawn chorus of birds, the unique Anuran cacophony has its own particular charm.Â
We set out to do acoustic sampling at a number of different ponds and pans on campus and outside. This consisted of placing programmed audio recorders, about the size of a camera trap, attached to a stake post or tree branch facing the habitat. Once we had finished setting these up, many of the students, guided by Dr Tarrant and her assistant Ella, went about the muddy, wet and playful search to catch live specimens to identify. We were reasonably successful in the hunt, finding a good number of species, from a sand frog to a golden leaf frog. Most of the frogs found were tiny froglets, often smaller than a fingernail.Â
Finally, we went through the various technical means to determine the different species present in the acoustic data. Unfortunately, unlike birds, there is no automatic identification app for frogs, so identification is much more labour-intensive. This is a major weakness that Dr Tarrant is trying to remedy, and she has been in talks with Google and Cornell University about the potential development of a frog-specific identification app. This would likely provide a crowdsourcing breakthrough for the field, allowing for more reliable data and greater interest from amateurs.Â
After that intensive frog course, I have grown a newfound fondness for Anurans and their quirky ways. So whenever you are doing a wildlife conservation plan for an area, remember not to forget the frogs, as many people do.Â