120 THE FINCHES 



siskin 1 only the female does. It is stated by Naumann, however, 

 that the male greenfinch occasionally, if rarely (ich erinnere mich nur 

 einigemal), takes his place on the eggs, and that the male house- and 

 tree-sparrow habitually do so. 2 



In each of the above two classes of activity nidification; namely, 

 and incubation as also in the relative share taken by the two parents 

 in the subsequent care and nurture of the young for in this the male 

 almost invariably renders some assistance an interesting field lies 

 open for future investigation. It is not sufficient, as in England it has 

 been long thought to be, to know when and where a bird builds, how 

 its nest may be recognised, what are the colours and markings of its 

 eggs. All this, especially the last, may be most absorbingly interesting, 

 but something more intimate and psychological remains, and until we 

 know, with some degree of fulness (which must include the habits and 

 relations of both the sexes in all these respects), how birds build, 3 how 

 they incubate, and how they rear their young, we have not torn out 

 the heart of their mystery. In all these, but especially in the two 

 first, there would seem to be an individually fluctuating element on 

 the part of the male, more particularly, which, if properly studied, 

 might lead us to conjecture how or why he first adopted or gave up 

 the habit, and thus gain some insight into the causes of the differentia- 

 tion of the sexual relations in regard to it. 



The greater number of our finches feed their young with seeds 

 that have been first swallowed and softened in the crop, as, for 



1 For all these see ante, "Classified Notes," under Finches. For the mealy redpoll see 

 Collett, quoted in Sharpe and Dresser and in Naumann. 



1 Ibid. Owing to the number of opposed assertions, and the difficulty there sometimes is in 

 knowing whether they are from the writer's observation, it is almost impossible to state the 

 facts uninfluenced by the personal equation. My own, for example, gives more weight to 

 affirmative statements than to negative ones, it being easy to miss a bird that has either been, 

 or is coming, to the nest, but not so easy to see it there, if, in fact, it is not there. Unless we 

 are told, internal evidence must be the guide as to whether or not a statement is from personal 

 knowledge. 



3 It is through observation of this, as I believe, that the origin and philosophy of avine 

 nidification is to be discovered. I have, as I think, brought forward good, though not extensive, 

 evidence to show that the practice has grown out of those nervous, and often violent, move- 

 ments, at a certain season, which, along another path, have led to the nuptial display. Both, 

 in my opinion, have been made out of the same raw material. See my paper in the Zoologist 

 for December 1901, vol. v. pp. 459-462, and April 1902, vol. vi. pp. 1,33-144. 



