274 Cleland, Birds of the Pilliga Scrub, N.S.W. [ispAprii 



town). Dingoes were not heard by us, but others speak of their 

 howhngs. One kangaroo and no wallabies were noticed. Even 

 rabbits were few, except in occasional favoured spots ; thus, over 

 one stage of about 14 miles only two were counted, over another 

 of 24 miles 12, and over one of 12 miles 23. Even human beings 

 were few, and none was seen between 15 miles from Narrabri 

 and the same distance from Baradine. In the centre of the area 

 a few March-flies {TahanidcB) were seen, and occasional mosquitos 

 were caught. Later in the year the latter seem to be numerous. 

 Even ants were not very abundant, though, of course, present. 



In spite of this relative absence of animal life, about 83 species 

 of birds were recognized during the journey of ten days over the 

 189 miles of country, and approximately 1,604 individuals of 

 these species. The assessment of the latter may be more fully 

 explained. For over eighteen months previously I had made it 

 a practice, when making a through journey by foot, driving, or 

 by motor-car, to note on a slip of paper the species of birds seen 

 and the numbers of each species met with. To those acquainted 

 with the flight, the shapes, and colouring of Australian birds, 

 together with their habits and notes, it is not difficult to recognize 

 with reasonable certainty many or most of the species disturbed 

 by one's progress along a road or on a track, provided a fair view 

 is obtained. In some cases doubt will exist as to whether the 

 bird is one or the other of two related species. In other cases 

 only a glimpse is obtained, or the bird may be at some distance, 

 and so a guess can alone be made. On the whole, however, my 

 experience, over many different types of country from Broken 

 Hill to the North Coast of New South Wales, has been that 

 relatively reliable results are obtained as regards most of the 

 species met with, and it seems reasonable to assume that the 

 numbers seen represent at least a minimum for the bird population 

 in the area over which observation has been made. By a 

 " minimum bird population " I mean that at least the number 

 of individuals recorded as seen exist in the area. This, of course, 

 is not to be taken as meaning that, in the type of country con- 

 cerned, the minimal numbers of individuals of each species, 

 actually present in any particular belt at one time, are only those 

 thus recorded. The actual numbers of birds present in the 

 observed area may be really much larger, and is probably nearly 

 always considerably larger, than the numbers actually seen, as 

 many must have escaped observation. As regards some species 

 {e.g., Grallina and Gymnorhina), the numbers seen probably 

 approximate closely to the numbers present. In other cases, 

 as amongst the Acanthizce, the numbers are probably far greater. 

 On the whole, however, it may be said that the observed numbers 

 do give us some indication of the density of bird-life, and arc 

 certainly a very conservative under-estimate of the true popula- 

 tion. What, of course, they more clearly indicate is the number 

 of birds of each species one may expect to see over a journey of 

 such a distance by such and such a means of progression. That 



