CHAPTER XVIII 



BIRDS, CONTINUED. MISCELLANY. MIMICRY AMONG BIRDS. THE BRILLIANT, 

 FLOWERLIKE COLORATION OF "HUMMINGBIRDS' HEADS NOT MIMETIC. 

 SEXUAL DIFFERENCES OF COLORATION 



npWO kinds of ' Mimicry' have been described by various authors as oc- 



curring among birds; first, the form distinguished as "Protective Re- 

 semblance," in which a live animal counterfeits the appearance of an inani- 

 mate thing, and second, so-called Mimicry proper, in which one animal 

 counterfeits the appearance of another. But of Mimicry proper among 

 birds few instances have been cited, while Protective Resemblance has been 

 supposed to cover most branches of avian (as well as mammalian, insectile, 

 etc.) protective coloration, including the many which we have already shown 

 to belong to the very different principle of obliterative coloration. The ques- 

 tion of " protective resemblance," indeed — the mimicry by animate of inani- 

 mate things — is somewhat closely involved with certain phases of the oblit- 

 erative coloration of birds, and must be considered here. I have mentioned 

 it several times in the preceding chapters, in connection, for instance, with 

 bitterns, goatsuckers, ruffed grouse and screech owls. In all these cases, 

 the principle has either been dismissed as having no true application, or has 

 been shown to be subordinate to the laws of obliterative coloration. The 

 ruffed grouse and the screech owl draw their feathers tightly to the body, 

 making themselves as thin and sticklike as possible — and this might be 

 called mimicry. But, as I have explained, this very action is essential to the 

 perfecting of their exquisite picture-patterns, which imitate the details of their 

 more or less distant backgrounds, rather than the markings on a single fore- 

 ground branch or stub. The bittern, likewise, with head and neck held stiffly 

 upright, might be supposed to be mimicking a stick, but a more critical in- 



ioo 



