Our rare native frogs

Press, 15 April 1980, Page 20

Our rare native frogs

There was life in the ■sea long before the land was inhabited. The first creatures to venture on to the land were the amphibians, large animals that lived in swamps and mud pools, returning to the water to lay their eggs. The descendants of these ancient amphibians are frogs, toads, newts and salamanders found in different parts of the world.

The only amphibians to be found in New Zealand are six species of frogs — three native, and three in-, troduced from Australia.

Not many people have seen the native frogs because they are few in number and they hide away in isolated places. Perhaps these secretive habits have enabled them to .survive in much the same form as their ancient relatives of 150 million years ago.- The three species of the New Zealand native frog, and one

North American species, are believed to be the four most primitive frogs in the world.

Gold prospectors found the first native frog in 1852 when they were washing the soil of a mountain stream near Coromandel on the East Coast of the North Island. Some years afterwards more frogs of the same species were found under stones near the tops of the Coromandel Mountain Range, far removed from water.

Early this century a second species of native frog was found tinder stones and boulders on Stephens Island, a wildlife reserve in Cook Strait.

In 1942 a third species was identified, but this one had been seen many years before. However it had not been examined by a naturalist and proved to be a different species from the Coromandel frog. The., three rare species of native frog are known

to be able to live under rocks and stones far away from water, although the Coromandel frog is more often found near water. The toes of its hind legs are half-webbed. The other two species show little evidence of webbing, The New Zealand frogs are small — about 20 mm to 47 mm long. They retain a number of features of their ancient ancestors that distinguish them from frogs of more recent origin. Like all frogs they breathe . through their skins as well as their lungs, and their skins must be kept moist. They depend on rain, dew and mountain mist for moisture.

An interesting difference in the habits of the small native frogs is in the way the young are hatched. At this season many of you will have collected frogs’ eggs in nearby ponds' and streams to watch the life cycle. The egg hatches into a tadpole

living in the water ' and feeding on vegetable matter until it has developed to a stage when it can feed on insect larvae.

You will have’ seen the back legs grow and have waited for the last stage when the forelegs appear and the tail drops off. The native frogs, living as they do far away from water, have adapted to thej rough conditions by short- : cutting the tadpole stage. The egg is laid in a small ; oval-shaped case containing a watery fluid. Inside the case the egg develops into a froglet, missing out the long tadpole stage. Naturalists have observed the eggs of two of the native species and watched the way they develop, but this is not considered to be a characteristic inherited from their ancient ancestors. It is an example of the way they have adapted to living away from water.