by John Walsby
If you asked a class
of primer children what animals lived in ponds and streams, the
first to come to their minds would probably be frogs and tadpoles.
Most would be less aware of the other creatures described in the
other articles in this series. Many of you have probably collected
tadpoles and kept them in a bowl when you were younger. You were
lucky to be able to do so in New Zealand for, if two closely related
species had not been introduced from Australia in the middle of
the last century we would not have tadpoles in our streams and
ponds in the summer.
We do have native frogs in New Zealand, but all three species are very rare and none of them have free-swimming tadpoles. Instead of laying long strings of eggs in a spawn mass in water, our native frogs lay just a few large eggs in damp places beneath stones and logs. The tadpole stage is completed within the eggs and when they hatch it is small froglets that emerge.
You are unlikely to see any of our native frogs unless you make special expeditions to find them. The frogs that you do see around ponds, lakes and swampy land are either the golden bell frog, Litoria raniformis, found throughout New Zealand, or the green frog, Litoria aurea which is confined to the northern half of the North Island.
Both of these frogs are handsome animals growing to 75 - 90 mm at full size and coloured green with golden-brown blotched markings. Those seen hopping along roads at night in the spring are probably on their way to favoured breeding ponds to mate and lay spawn.
The young tadpoles feed on algal films but about the time they start to grow leg buds they start taking small animals in the water. As the hindlegs, then forelegs develop, the fishlike tail is steadily resorbed as the change from tadpole to froglet occurs. Froglets leave the water but stay close by so they can always return to keep their skins moist.