304 Sex Habits of the Great Crested Grebe. 



their throat or upper breast, and as the head was again raised, 

 after having been sunk to allow of this, it was given a twitch 

 or jerk, or two, which combined action became habitual. 

 This perhaps is not very strange, for those same constitutional 

 causes which produced preening, in other parts, would probably 

 have done so, to a special degree, had it been possible, amongst 

 the sun-flower-like feather-wealth of the head, set delicately 

 on its slender, bending stem, the neck. No bird, however, 

 can preen its own head. To twitch, or shake it, therefore, 

 is perhaps the next best thing it can do, until the matter, 

 becomes sufficiently urgent for the employment of the foot, 

 and this, if carried to any undue degree, would be hardly 

 compatible with the welfare of the species. Whatever the 

 link, or even if there is none, we at any rate have, as Huxley 

 has shown, this habitual combination of throat or breast- 

 preening, and head-twitching or shaking.* Starting from 

 that, I have elsewhere put on record| the amount of hesitation 

 there habitually is, in these Grebes when intending to pair, 

 which produces a large number of abortive pilgrimages to the 

 nest, for this purpose. The nervous emotional state of the 

 birds seems, as it were, to have carried them to the brink of 

 the act, but a further uprush of sexual desire is necessar}^ to 

 take them over it. Let us suppose that with a pair of them 

 about to neb, there was, in the past, before head-shaking had 

 become fully developed, the same thing. There would then 

 have been continual pausings on the threshold of the con- 

 templated action, and these were filled up (pauses must be 

 filled up, in some way) with a greater or lesser number of 

 preenings of the throat or breast, mostly — sometimes else- 

 where — and twitchings, or slight shakes, of the head. So 

 much was this the case that such half-nervous movements 

 began seriously to interfere with the nebbings till, at last, the 

 birds, being unable to prevent themselves falling into them, 

 came to accept them, first, as a subsidiary, then, as the more 

 important, and finally, as now, perhaps, in a majority of 

 cases, the sole object of their comings together. Such a 

 process would, of course, have gone hand in hand with a 

 corresponding increase both in such motions and the pleasure 

 derived from them, till, at last, the principle of sexual selection 

 concentrating, as it were, on the head-shakings, may have 

 carried this to the pitch which Huxley has seen, but I, not 

 being able to stay on longer, have not. In this way, actions 

 which were, at first, merely nervous or alleviative, or both 



* Luc. cit., p. 315. If, as 1 have surmised (see niite) prcenini; alone, 

 without head -shaking, fills up the pauses before coition, this is interesting, 

 as shewing a suspension of the lesser sexual (as it has now become) by 

 virtue of the greater ; but the argument is left unaffected. 



f Zool., ^lay, 1901, p. 1&5, etc. 



Naturalist 



