302 University of California Publications in Zoology. \y°^- ° 



in the family of wrens which an amateur can usually recognize 

 by noting the superficial color pattern. A similar tendency 

 appears in the vireos and also in the flycatchers. If, therefore, 

 we find white patterns conspicuously lacking among Troglo- 

 dytidae, Vireonidae and Tyrannidae, we are bound to consider 

 whether or not this may be partly due to the stability of a type 

 (intrinsic influence) or to selective influences alone. The occur- 

 rence of a perfect adaptation at variance with the type in the 

 bleached, sand-colored monochrome of the Leconte thrasher 

 {Toxostoma lecontei) indicates that the Troglodytidae may not 

 be exempt from the strict enforcement of the principles of 

 adaptive coloration, where the conditions of their life demand it. 



There are some relative differences among birds that might 

 conceivably enter into the explanation of correspondences in 

 color, but apparently do not to an appreciable extent. Size is one 

 of these. The only way in which it appears to affect coloration 

 is by affording immunity from enemies. Size combined with 

 vigor and aggressiveness opens the way for conspicuous colora- 

 tion. But the need of concealment on the part of the aggressor 

 neutralizes the effect of this immunity in most cases. The raven 

 is one of the exceptions within the order of perchers, and the 

 condor, Egyptian vulture, and turkey buzzard, outside it. These 

 are birds that need no concealment for aggression, but profit by 

 a conspicuousness that makes them recognizable to each other at 

 great distances. 



As for warning coloration, there seems no reason for believing 

 that it occurs among perching birds. "Were the principle thor- 

 oughly established we might be justified in regarding the magpie 

 as an instance ; but since other functions may readily be assigned 

 to the contrasts in its plumage, and since these are not necessarily 

 utilitarian, as the bird is largely "immune," the whole hypothesis 

 is negligible for the birds under discussion. 



Temperamental differences form another set of elements to be 

 considered. A search for correspondences in this direction shows 

 at least a few well attested instances of boldness of disposition 

 accompanying the supposed conspicuousness of plumage. Such 

 are the kingbird (Tyrannus tyrannus), the scissor-tailed 

 flycatcher {Muscivora forflcata), the mockingbird (Mimus poly- 



