Frogs from Australia

Press, Volume CXIII, Issue 33141, 3 February 1973, Page 11

Frogs from Australia

The two frogs shown here were photographed recently in Westland. One is the brown whistling frog (Ewing's hyla), and the other (lower) is the common green frog (Hylaaurea). The whistling frog has large toe pads. The green frog’s toes are rather pointed, and it has a large ear drum just behind the eye. The green frog is about 1| inches long and the brown a little less than an inch. Notice the plumpness of the green one. He has just swallowed a whistling frog, which but for this unfortunate incident would have had its portrait in “The Press.” “Frog is the preferred food of frogs” to quote an authority on the subject, but this fact was overlooked when the two specimens were put into the same container to await the photographer. Cannibalism is a regular method of population control in the frog world. Both frogs were introduced from Australia to provide food for ducks and it was thought also that the whistling frog would control mosquitoes. These frogs do not belong to the family of rana, the true frogs, but are tree frogs, closely related to the toads.

The toe pads are easily seen features, exclusive to tree frogs. There are no true frogs in Australia or New Zealand, but the genus hyla (tree frog) comprising over 300 species is well represented in Australia. In some places the whistling frog is called the native frog because of the similarity in colour and size to our rare native species. However, there is no need for this error, as the native frog has no voice, no toe pads and no visible ear drums. Nor does it come to water to breed; its tadpoles develop in a gelatinous envelope on land. Ancient lineage Our native frogs — which also are not true frogs—have a lineage more ancient than that of the dinosaurs and the still older tuatara. The common green frog is anomalous in that it has lost its toe pads, the distinguishing features of the tree frogs. Here we have an example of a tree frog that has changed its habits and taken up ter-

restrial life and the toe pads have been lost. This is a parallel to the loss of wings in flightless birds, and some flightless insects. The organ not used has become vestigial. The habits of the green frog have changed it to a creature very similar to the river frog. True, they still climb trees but always above water and leap not from branch to branch but straight down to the water. The leaping, and landing skill, of the whistling frog are remarkable. The eyes are large and well spaced to enable them to work to advantage in low light. The head is much more mobile than one would imagine for a neckless animal. A frog held on the hand studies his surroundings with alert eyes and head movements and will spring quite a distance to a stick or upright surface and

make a precision landing with instant immobility on impact; no shuffling of legs or drawing in of toes. The toe pads enable him to stick. The whistling frog occurs in much of the South Island but it is still most abundant in Westland where conditions suit it best. There are considerable populations in Southland and about Temuka. Most of the Canterbury rivers, particularly near the mouths, have small populations. There are several places in Christchurch where occasional chirpings may be heard on mild wet nights and various parts of the Lewis Pass area have a few whistling frogs. It is possible that most of the spread of this species has come from children’s lost pets. As for the green frog it is c’ear that he has spread unde, his own “steam” —A. G. McF.