Tailormade African Safaris by the Safari Legends
There are many animals residing in the bush of Sabi Sand Game Reserve, some that only come out when the right circumstances present themselves. And so it was on the morning of 29th of December 2016, after a heavy night of rain, we got an unexpected glimpse into the world of the park’s resident amphibians.
To our surprise, the muddy water’s edge was flecked with bulbous lime-green heads of mature male bull frogs and the entire area was alive with the sounds of their calls. Although they may look similar to an ordinary wetland/marsh frog, these noisy critters are a lot more interesting than they seem.
There are two types of bullfrog residing in the Sabi Sand Game Reserve; the Highveld bullfrog (giant) and the African bushveld bullfrog (dwarf). While not actively recognised as endangered, the African bullfrog has been noted as ‘near-threatened’ in South Africa. These frogs are only found in the highveld and lowveld areas during certain times of year and are actively threatened by human activity.
According to the local staff, it was the first time in four years since these frogs were last seen. This coincided with a period of torrential rainfall in 2012/2013. Since then the bullfrogs have been in aestivation. What this means is that they have been in a state similar to hibernation. This is where the frog will become dormant for a time; spending its days and nights below ground, not emerging until cooler conditions present themselves. During aestivation, the metabolic process of the frog will slow down and it will live off of its own bodily reserves.
The frogs burrow down deep into the earth and only resurface when the summer rains are at their highest. Research shows that the frogs will only come out when the rainfall is more than 50mm as is the case on the night we spent in the park. It has been recorded that a bullfrog can stay underground for up to seven years! Once they are safely tucked away in their burrow, the frogs are protected from freezing cold winters and the scorching summers. The frogs are brought up to the surface when the rain soaks through the soil into the burrow, triggering an emergence.
A noisy morning after the rains
Once on the surface, the frogs gather along shallow parts of dams and pans and begin their spawning period. This is where the frogs are at their most vocal. The male bullfrog breeding call is a throatily, low sounding “whoop”.
Their objective in the first four days is to mate and challenge rival males. After spawning, tadpoles will hatch after two days and will continue their metamorphosis over a 30-day period.
The frogs we witnessed were not the biggest, male bullfrogs can reach a top weight of almost 1kg and an average length of 17cm from snout-to-vent.
Bullfrogs are also unique in that they have what is known as odontoids. These are tooth-like structures in the middle of their lower mandible. While not poisonous, the frogs can bite, causing a nasty painful wound. It is advisable not to dangle your fingers in front of a bullfrog!
If you are lucky enough to find a bullfrog, the best thing to do is photograph it, record when it was seen and send the information through to: Dr. Jeanne Tarrant of the Endangered Wildlife Trust Threatened Amphibian Programme.