Tuesday, February 8, 2011


Driving around Mwiba ranch you can’t help yourself but wonder what all the different sounds are that you hear. Leaving aside wilddogs whooping and yipping, lions roaring, leopards grunting, buffalo bawling, the impala alarm calls, there are all the piercing noises made by insects and frogs. Grant and I decided to set off one night, grabbing our maglites we drove to the nearest stream took off our shoes and waded in.

Frogs require water to lay their eggs in and males hang around in the water, on vegetation around the water calling for females to come and mate. Some have developed fantastic large airsacs in their throats that the blow up to amplify the sounds that they make. It’s a competition, so their sounds tend to be extremely loud.

The first 10-15 minutes of wading around in the water were quite frustrating at the frog’s amazing ventriloquy abilities Frogs are also surprisingly camouflaged, and it takes a few minutes before your eyes become trained to pick them up from wherever they are calling. Part of the reason their so hard to see is because most of the time they stop calling when they sense a predator (or are blinded by a maglite) so you have to sit still and wait for them to start calling again. The other problem is that once they’re in the water they are nearly impossible to catch.

Nevertheless, during the 3 nights we went frogging we managed to catch 5 different species (+ 2 species seen on walks).

The most beautiful was this East African Tree Frog (Chiromantis petersi) also known as an East African Foam Nest Frog. They get their name from the fact that they don’t spend most of the time in water but end up hoping around on trees and as you can see from the photo they blend in very well. In fact they can change color from dark to almost white. Foam nest frogs don’t lay their eggs in water, but when the males climbs on the females back as she is laying eggs, he starts to move his legs whipping up a mucus excretion into a foam that protects the fertilized eggs. It’s a skill that has intrigued scientists studying it because making a foam nest suitable for protecting eggs has interesting medical implications like protecting burns from drying out and protecting wounds in emergency care. If you’d like to read more about this check out this link http://news.bbc.co.uk/2/hi/science/nature/8481102.stm

East African Foam Nest Frog (Chiromantis petersi)
The other star of the night was a Muller’s Platana or Muller’s clawed-frog (Xenopus muelleri) that Grant managed to catch because it has trapped itself in an elephant footprint that had water in it. In contrast to the Tree frog, this Platana spends most of the time in the water. I think Platanas look quite amusing, but I wasn’t so amused when I tried to grab one and it swam just out of reach taunting me to try again- another miss. (No wonder herons have 27 vertebrae in their necks- arranged to form an S that straightens like a rocket to catch frogs). These funny looking frogs can actually call from underwater and it sounds like someone knocking a spoon against a pan. (photo coming soon)

The other frogs we found were- the Tremolo Sand Frog- (Termopterna cryptotis), a Reed frog (Hyperolius sp. prob. H. glandicolor), and a Puddle frog (Probably Phynobatrachus acridoides or P. natalensis). Unfortunately, species identification is quite difficult unless you know the sounds and the best we can do using the South African sound recordings is confirm identification to the genus level. Thanks to Grant Burden for getting me in the water with him and keeping me from getting too frustrated with the keys, and to David Moyer for looking at photos and helping with Id.  

Tremolo sand frog (Termopterna cryptotis)
Reed frog (Hyperolius sp1. prob. glandicolor)
Puddle frog (Phynobatrachus acridoides or P. natalensis)
Reed frog (Hyperolius sp2. prob. viridiflavus). Photo credit: Colin Beale Jan. 2011.
Young African Bullfrog (Pyxicephalus adspersus). Photo credit: Colin Beale Jan. 2011.

No comments:

Post a Comment