Coloration of the Mouths and Eggs of Birds. 283 



warning colours." Any additional advantage the twin spots 

 may possess as directive markings would doubtless also have 

 contributed to their retention. 



Chloropeta natalensis (figs. 9, 33), a Flycatcher with a very 

 vivid Warbler-like mouth, falls into the same colour-group at 

 Chirinda as Cisticola cinerascens (figs. 10, 11) and Prinia 

 mystacea (fig. 8), an abundant Warbler that, experimenting 

 with adult and still immature birds, I found to be fairly 

 low-grade — disliked, that is, to a fair extent by the animals 

 I tried it on. The three birds inhabit the same " veld " — 

 grass country interspersed with bracken, low shrubs, &c., 

 and they build at about the same height from the ground, 

 and thus probably possess the same nestling enemies. So 

 that the resemblance, if, as I think, it is advantageous to the 

 Flycatcher, is probably being retained by selection to-day 

 whether it originally arose as mimicry or by coincidence 

 pure and simple, or from the retention of or reversion to a 

 mouth-pattern more ancestral than the present spotless 

 mouth of its relations. The rejection of the present 

 normal colouring might have been associated with the 

 Flycatcher's taking to a new kind of station (as it has done) 

 and so coming in contact with the enemies of the Warblers 

 whose station it had invaded instead of its old enemies, 

 acquainted with the plain orange Flycatcher mouth such as 

 would often be met with in bush country ; and its new lack 

 of notoriety might have been the main factor in bringing 

 about the selection of the likeness. At any rate, my experi- 

 ments with the adult birds do not lead me to suppose that 

 nestling Chloropeta is likely to be better liked by enemies 

 than nestling Prinia. That Chloropeta batesi, of southern 

 Cameroon, should have the same mouth is, in itself, no 

 objection to this view. The resemblance to a yellow- 

 mouthed Warbler may have arisen first in an ancestor of 

 the two species and have continued in themselves through 

 the advantage it still afforded them, much as I suggested for 

 the distinctive mouth of the Warblers. 



Reseinblances, and particularly resemblances in such 

 simple patterns as we find in birds' mouths, so often arise 



