Life In Cold Blood
Invaders Of The Land – programme two
Among chorusing frogs in Panama, Sir David Attenborough asks how amphibians first managed to invade the land. The Australian lungfish, an ancient relative of the amphibians that can breathe air, and the giant Japanese salamander, one of the largest amphibians on Earth, give vital clues about their first tentative steps. These giant land invaders also demonstrate fiercely protective parenting skills.
In a disused goldmine, David finds salamanders that no longer need water. The mine walls glisten with dozens of female western slimy salamanders guarding their eggs and young. They are ready to put up a fight against other predatory hungry females, who see their young as a source of nourishment.
The primitive worm-like caecilians demonstrate parental care never filmed before. The mother produces a rich secretion and the young lap it up like milk and, more bizarrely, they also eat her skin, tearing at it like mini sharks. She is unharmed and regularly feeds her babies in this way.
But in some amphibians the fathers do the work. The male of the beautiful poison arrow frog, in Peru, carries each of his tadpoles on his back before depositing them into their own individual breeding pools. He guards them, and, when one needs feeding, calls in the female – leading her to the right pool, where she lays an infertile egg as food.
A TV first reveals the intensely protective parenting of the marsupial frog, in Australia, who guards his clutch of eggs until they are ready to hatch and then straddles them to allow the tiny white tadpoles to wiggle into two special pouches on his hips. He carries his growing family around for several weeks and then "gives birth" to tiny, perfect froglets.
In Panama, David meets the rare golden frog – filmed for the last time in the wild. It communicates with its rivals and mates by semaphore in the form of gentle hand waves.
Amphibians have even made it to the driest of places. The rain frogs in South Africa live underground, emerging from the soil when the first rains arrive. The males are too small to grasp the fat females so produce glue that helps them stick. Unfortunately, it makes them stick to other males, too. Once paired, the females dig underground – taking the tiny attached male with her. Below the soil, she makes a special chamber for her eggs and even secretes a moist foam to provide the young with their very own underground pond.
Finally, David ends up in the baking deserts of Australia. Even here, a desert spade foot toad can live without water for two years – living proof that amphibians have truly conquered the land.
Under The Skin – Warning From The Wild
The filming of the bizarre semaphoring behaviour of the Panamanian golden frog was to be a race against time. Already threatened by habitat destruction and
over-collecting, a killer fungal disease was now moving towards their last remaining forest stronghold.
Series producer Miles Barton cut short his Christmas holiday to join the crew and frog biologist Erik Lindquist at the top secret location in the Panamanian rainforest. After being fully disinfected – so that they don't carry the disease – the crew eventually filmed the frogs waving, wrestling and courting for the first time.
When David joined the team the fungus had reached all but one final mountain stream. Erik showed him how to find the last remaining frogs by calling to them and prompting them to respond. He used mirrors and a life-size waving plastic model frog to demonstrate how he, and other scientists, discovered that the golden frogs were indeed communicating with each other. They even tested the response of wild frogs to one waving on a TV!
Sadly, not long after the filming, the location was overtaken by the chytrid fungus and the scientists rescued the surviving frogs, bringing them into a frog hospital to be cured of the disease. So, for now, the golden frog has waved for the last time in the wild.
- Giant salamanders are the largest amphibians in the world, and can be over a metre-and-a-half long.
- The tiny painted reed frog has the loudest frog call for its size. Chorusing males can be heard over a mile away from their breeding pools.
- The Mount Lyell salamander has a tongue that is three quarters the length of its body, and can be shot out in one thousandth of a second.
- The male giant African bull frog guards a crèche of thousands of tadpoles and digs a drainage channel to release them into deeper water if their pool dries up.
- The Australian desert spade foot toad can stay underground for up to two years – it absorbs water through its skin and takes this supply below ground.