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Tuatara: Volume 18, Issue 1, July 1970

Observations on the Effect of Chlorinated Town Supply Water on A Colony of Brown Tree Frogs (Hyla Ewingi) in Foxton

page 45

Observations on the Effect of Chlorinated Town Supply Water on A Colony of Brown Tree Frogs (Hyla Ewingi) in Foxton

The brown tree, or Whistling, Frog (Hyla Ewingi) though limited in its New Zealand distribution, is reasonably numerous in the town of Foxton. I have found it in several gardens, where it survives well in large clumps of Agapanthus.

In October, 1969, the Foxton Borough Council chlorinated its water supply, and this appears to have been detrimental to the existence of the frog. During the breeding season (spring), I noted that several horse troughs in the town no longer contained tadpoles. In previous years I had collected many from the same spots, and their disappearance was obviously caused by the new water supply. I also visited a neighbour's goldfish pond to observe the hatching frog spawn. The adult frogs that lived in the plants surrounding the water were still there. The pond, however, had been filled with chlorinated water, and the goldfish had died. The frogs, though they entered the water themselves, had found the pond unsuitable for spawning and no eggs were to be seen.

Nearby there stood an open concrete tank that had not been used for months. It contained about 2½ inches of rainwater, and into this the frogs had deposited their eggs. Soon the tadpoles hatched by their hundreds, and, as the food supply was virtually negligible, I scooped them up and released them into an unpolluted pond. This was fortunate, for two weeks later, the tank dried up during a particularly dry spell of weather.

Perhaps the frogs will become chlorine-resistant, or possibly the colonies near fresh water will keep up the numbers, for it would indeed be sad if Hyla Ewingi were to disappear from Foxton.