NO. 7 PROTECTIVE ADAPTATIONS McATEE I3I 



numerous broods. Birds have other external as well as internal para- 

 sites also, the relation of which to mortality is not well known. An 

 occasional bird falls a victim to mussels or other bivalves, to cray- 

 fishes, and to mantids and spiders. 



Discussion. — " Warningly colored " ncarctic birds, according to our 

 tabulations, are eaten along with the others, the common ones fre- 

 quently, the rarer ones to a lesser extent. Our most extensive family 

 and the one most numerous in individuals, occupies the logical, if 

 unenviable niche, as the most important contributor to the subsistence 

 of predatory species. This family, the finches, includes many of the 

 most " protectively colored " species. Fortunately there is other direct 

 evidence of the way in which nearctic predators react to protective 

 coloration. I refer to Dr. Raymond Pearl's paper on the " Relative 

 Conspicuousness of Barred and Self-colored Fowls" (Amer. Nat., 

 vol. 45, pp. 107-117, Feb., 1911). Natural enemies cai)tured in one 

 year 325 individuals out of a total of 3,443, a flock which contained 

 both barred and solid-colored fowls. By all theories of protective 

 coloration, the latter are the more conspicuous and should pay a 

 higher toll to predatory enemies. Of the total number of birds 10.05 

 per cent were self-colored and of all the eliminated birds 10.77 P^^' 

 cent were self-colored. Thus these monochrome birds were taken 

 almost exactly in proportion to their numbers in the whole flock. This 

 is precisely the result that would be expected by those who have 

 learned by study of the subject that availability is the one strongest 

 factor in choice of food by predators. With availability as the con- 

 trolling factor it follows that in the long run, and on the average, 

 losses to predators will be very closely in proportion to the relative 

 abundance of the group concerned. 



Mammalia (Mammals) 



Protective adaptations. — Many of the mammals are conceived to be 

 very perfect exemplifications of protective or cryptic coloration. A 

 few are credited with noxious qualities, accompanied in the case of 

 the skunks only, in our fauna, by warning coloration. The short dense 

 fur of moles and shrews is said to be a deterrent to predators and 

 these animals are thought to be protected by a strong musky secretion 

 also ; shrews have even been credited with poisonous bites. However 

 the most potent defenses of mammals in general against birds are 

 their large size, and their teeth and claws. 



Bird enemies.- — Despite the size and direct means of defense of 

 many species, mammals pay a heavy toll to bird predators. In our 



