I 78 MlLLiGAN, Observations on the Western Gymnorhince. \ £ m T u 



necessity be compelled to probe deeply, perhaps to the full extent 

 of their bills, or nearly so, in quest of their daily food ; and these 

 very acts, oft repeated, as they must be, would tend to and would 

 in course of time develop the bill both in length and girth. As 

 a counteraction, however, to the girth development, the same 

 repetition of the same acts would, by the fact of the bill meeting 

 with harder substances than itself (that is to say, the vitreous 

 sand granules), cause the bill to become attenuated by trituration. 

 In Eastern Australia the soils of the agricultural districts, wherein 

 the birds are principally found, are moister and more cohesive, 

 and are better protected from a milder sun by a natural clothing 

 of grass, the surface roots of which, more important still, form 

 the natural home of the lower forms of life before referred to. 

 As a consequence the natural food supplies of the birds are nearer, 

 if not actually in, the surface soil, and a shorter bill serves the 

 purpose of obtaining them. And if the bills of the Eastern forms 

 be closely examined it will be readily seen that the depth to which 

 they are probed in quest of food is the beginning of the distinct 

 arch of the culmen. Again, the contact of the bill with the 

 moister and less granulous soil does not cause friction in the 

 same degree and consequently a corresponding reduction in 

 girth: Collaterally, and perhaps in combination with the above 

 theory, I might have advanced even with greater force the well 

 laid and accepted principle of natural selection. Repeating what 

 has been said in reference to the daily quest of food by the Western 

 birds, there would, I think, accepting that principle, be a tendency 

 to an increased length of bill. Birds with bills of short or of 

 medium length would on the average be placed at a considerable 

 disadvantage in search of their daily food, while birds with bills 

 of a more appropriate length would correspondingly be placed 

 at an advantage, and so tend to survive and to leave progeny 

 mheriting the same characteristic. Such " survival of the fittest " 

 (that is, of birds whose bills are longer) would go on until the 

 length of bill best adapted to the conditions of their existence was 

 attained. 



My answer to the second question is that the absence of "hilarity 

 of song " is due solely to the peculiarity of climatic conditions. The 

 sudden and spontaneous outburst of song is invariably simultan- 

 eous with the termination of a period of privation or enforced 

 rest. In the latter respect birds in a natural state undoubtedly 

 sing more hilariously in the early morning, after a period of 

 darkness and rest. In countries where the winters are rigorous, 

 and particularly where the surface of the earth and the vegetation 

 are covered with snow for a comparatively lengthened period, birds 

 of purely local habits or enjoying only a restricted range suffer 

 privations. Consequently, what is more natural to them than, 

 on the relaxation or removal of those severe conditions, that they 

 should give full vent to their only mode of expression, namely, 

 that of song ? It is a fact that many birds, such as the Limicolce, 

 evade the rigours of winter of Northern Europe and Asia by 



