1922. | Mound-building Birds of Australia. 707 her neck and breast against the egg-chamber is quite unique, and suggests the possibility that this action is part of the method by which the birds ascertain the temperature of the enveloping sand.

My opportunities of personally observing these interesting and shy birds in their native haunts have been too brief and too far apart to furnish conclusive data, but, from my own observations and from the information supplied to me from time to time by dwellers in the back blocks, I have long felt satisfied that it is the regular habit of the Mallee-Fowl to open out the nesting-mounds almost down to the eggs on clear, hot, sunshiny days—this opening being done as soon as the sun is well up. ‘The sand is rather widely distributed and heated by the sun’s rays to a high degree. The birds always return fairly early in the afternoon, which accounts for Mr. Mann’s observation ** that he is under the impression that they are not long left open”’”—he seldom passes the nestingmounds on his way home from work till late in the evening, —the object of the birds’ return being to restore the heated sand to the nest. The accumulated heated sand retains its high temperature, or a large amount thereof, for some days. It seems evident that the mounds are not opened by the birds (except for actual egg-laying) on cool cloudy or drizzly days, the birds awaiting the return of a clear sky and the heating power of an unimpeded sunshine. In the districts where Mallee grows this is the normal weather.

In my lectures on Australian Bird-life before Agricultural and Horticultural Societies and other Public Bodies in the State of South Australia, I have often during the last few years told the story of the Leipoa, and expatiated upon the wonderful adaptation of its methods to changed climatic conditions, suggesting the following hypothesis by way of explanation.

As is well known, the interior of Australia used to be favoured with a much heavier rainfall than is now the case. The discovery of numerous skeletons of the huge extinct Diprotodon half-buried in the dry bed of what was once a