282 Mr. C. P. M, Swynnerton on the 



by them, of a nestling they are not hungry enough for, from 

 that of such species as they are, at the moment, hungry 

 enough for. It is quite true that an insufficiently hungry 

 enemy may come back when he next is hungiy enough, and 

 in the immediate neighbourhood; but the chance has been 

 given to the parent birds to remove their young (and they 

 often take the hint), or even to bring them off in safety 

 before the nest is revisited — as we ourselves, wishing to rear 

 the young birds, sometimes find has happened. 



The conspicuousness of many of the mouths, as apart 

 from mere distinguishability, is doubtless of use in impress- 

 ing their appearance on the enemy's memory and facilitating 

 their recognition when seen again. It is for readier recog- 

 nition ; and the selection and development of this character 

 have thus been rendered possible, in spite of the apparent 

 disadvantage that the result may facilitate detection ; for the 

 mouth is only opened and its brilliant colours displayed when 

 the nest is approached and likely to be seen in any case. 



Mimicry — for protection or increased notoriety — may help 

 us to account for so^me of the mouths, though the matei'ial is 

 still far too scanty to admit of a positive interpretation. 



Take first the Warblers. The twin spots are probably an 

 ancestral character common through affinity to all such 

 Warblers as now possess them. That their retention may 

 have been in part due to their continued usefulness and 

 consequent selection is not, however, impossible. " All the 

 butterfly sub-families, which furnish the chief models for 

 mimicry, are remarkable for the uniformity of colour and 

 pattern throughout groups of species in each of the countries 



they inhabit A very strong family likeness runs 



through long series of species.^'' ^ This can be accounted 

 for by the advantage of maintained notoriety. It has not 

 brought about the resemblance — affinity sufficed for that, — 

 but it has tended to prevent divergence. If Warbler nest- 

 lings generally are to some slight extent unpleasant to their 

 enemies, their common retention of the characteristic mouth 

 may in the same way have been in part a matter of " common 

 * Poulton, ' Essays on Evolution,' p. 277. 



