Pebble toad's rock and roll life

Matt Walker, BBC News 15 Oct 09;

When confronted by a predator, some animals fight, others run while a few hide, hoping not to be noticed.

The pebble toad of Venezuela does something altogether different: it curls up like a ball and throws itself down the side of a mountain.
By doing so, the tiny creature bounces down the rocks just like a rubber ball.

This extraordinary tumbling behaviour has been filmed in slow motion by a BBC crew for the natural history programme Life.

The pebble toad ( Oreophrynella niger ) is tiny, measuring just a few centimetres long.



It lives on the top of a type of mountain known as a tepui, which occur across the Guiana Highlands in South America.

These table-topped mountains rise out of the rainforest, isolating the animals and plants that live upon them.

As a result, many of the creatures have evolved differently.

For example, the pebble toad is unable to jump very far, an inch being the furthest it can hop.

While there are no snakes living on the tepui, this lack of athletic prowess makes the toads vulnerable to marauding tarantulas, an ambush predator.

The ball position

So the toads have evolved a unique escape mechanism.

A threatened toad folds its arms and legs under its body, tucks in its head and tenses its muscles, assuming a "ball position".

Because the amphibian is mostly likely resting on an incline, it then rolls downhill like a dislodged pebble.

The toads travel far enough to escape the attentions of the tarantulas and often tumble into a crack or crevice where they are out of sight or difficult to reach.

The toad's black and grey colour also helps it blend in with its sandstone habitat.

The toad is so small and light that the forces of impact are too tiny to cause it any harm.

However, as well as being less than impressive jumpers, the toads do not swim well.

So while most that land in puddles survive, there are reports of toads drowning after tumbling into deeper pools of water.

The team located the toads with the help of biologist Dr Bruce Means, an Adjunct Professor at Florida State University, US and head of a non-profit conservation organisation called the Coastal Plains Institute and Land Conservancy, based in Florida.

Dr Means ventured up the tepui, located in southeast Venezuela, to find the toads.

assistant producer Mr Scott and cameraman Mr Rod Clarke then followed a few days later to film the action, using slow motion cameras capable of recording up to 2000 frames per second.

"The first time I saw one of the toads on a rock one morning, we saw each other, and I made some sudden movement, and it flicked itself back and flopped down into a channel at the bottom of the rock," says Mr Scott.

"We'd been told they do this thing and then it did it to me. It was an unusual thing to see at the top of a mountain. They just curl up and flop."

The tumbling pebble toad can be seen on the BBC series Life, which is broadcast at 2100BST on BBC One on Monday 19 October.