280 Mr. C. F. M. Swynnerton on the 



diversity — and not merely certain spots in the mouths of 

 nestlings in holes and domed nests. Such spots are as often 

 as not absent from mouths, which observation in the field 

 shows are often vividly displayed, wide open, in the brilliant 

 light of day through the opening in the nest on the latter 

 being jarred, just as the nestlings in open nests crane their 

 heads and open mouths upwards. The " directive " analogy 

 was from flowers. Nestlings, like flowers, "heliotrope." 



Pressing the analogy, I may say that, even in the matter 

 of flowers, it is recognised that the theory of directive 

 markings has sometimes been carried too far. As Kerner 

 and Oliver remark (Nat. Hist. Plants, vol. ii. p. 191): — 

 " It would be too much to say that all spots are to be regarded 

 as signals, or to call them ' honey-indicators ' or ' path- 

 finders.' " Markings in flowers are, in very numerous cases, 

 apparently useful only for giving them a distinctive appear- 

 ance (as, in another case, a plain colour might), whereby 

 they may be the more readily differentiated from the parent 

 form and other species by the pollinating insects, that prefer 

 them to these; and this '^ distinctiveness for recognition" 

 brings us down to an explanation which I believe to be 

 somewhat widely applicable to the distinctive coloration 

 of nestlings' mouths. 



Distinctiveness for ready differentiation by enemies. — I will 

 first quote, for what it may be worth, a conversation with 

 my native trapper, Mandina. It is recorded more fully in 

 my longer paper. 



" . . . . We went on to discuss nestlings. I said : 

 ' Have the nice birds always nice nestlings, and the less nice 

 birds less nice nestlings?' He said: 'No; nestlings are 

 always far less nice than their parents ; the younger they 

 are the unpleasanter they are, and we generally leave them 

 until they are, at any rate, getting their wing-feathers. 

 But even then they are not so nice as when they are 

 beginning to fly, and when beginning to fly they are less 

 nice than when full grown.' I said : * 1 know you usually 

 leave young nestlings to fledge before taking them ; but is 

 not this to get a bigger meal out of them ? ' ' Partly,' he 



