IOWA ACADEMY OF SCIENCES. 46 



It seems strange that such a striking assembhige of facts as is exhibited by 

 these concealed crests should have been left so long practically unnoticed by those 

 who make a special study of coloration. A partial explanation may be found in 

 the fact that no American has undertaken a serious study of coloration. The 

 Ti/nnniichr are all American, and British writers have had little opportunity to 

 study their habits. Another important consideration is that the writers on colora- 

 tion have concentrated their attentionalraost exclusively on insects, and have passed 

 over the birds with an entirely inadequate examination of these strikingly colored 

 animals. 



Let us now turn to the argument, which is based partly on elimination, partly 

 on the study of the habits of insectivorous birds in general, and partly on direct 

 observation. 



According to modern ideas all special organs or characters are supposed to be 

 of special use in the economy of their posessors.' 



Colors are useful to birds in many ways. These uses have been divided into four 

 general classes, protective, aggressive, directive and attractive. 



Protective coloration includes all cases where animals are helped in escaping 

 their enemies by their colors, either by a reseraolance to environment, which aids 

 in concealment, or by a mimicking of dangerous or distasteful forms. This in- 

 cludes both true mimicry and warning coloration such as is exhibited by skunks, 

 coral snakes, wasps, etc. It needs no argument to show that concealed crests do 

 not come under this head. 



Directive coloration furnishes a means by which individuals, particularly of 

 gregarious species, may keep track of their fellows after being scattered. The 

 crests of Fly-Catchers are probably concealed during flight and at any rate cannot 

 be seen at a sufficient distance to be effective as directive colors. 



Attractive coloration includes all cases when the colors serve to attract the at- 

 tention and secure the favor of the mate. They are generally, among birds at least, 

 secondary sexual characters and one usually considered to be a product of sexual 

 selection. They are apt to appear in the male only, or to be especially intense in 

 that sex. 



One of the most notable peculiarities of the concealed crests of the Fly-Catchers 

 is the fact that they are inviriablg possessed htj both' sexes. Among the sixty-one 

 genera examined by me, there was not one in which the male alone had a true 

 concealed crest, although in a few rare instances it was much more conspicuous in 

 the male, and in one, Muscivora mexicaua, the crests were equally conspicuous in 

 both sexes, but crimson in the male and bright yellow in the female. 



These crests, then, can hardly be regarded as secondary sexual characters, and 

 hence, cannot be considered as coming under the head of attractive coloration in 

 the technical sense ot the word. 



There remains but one more class of coloration, and that is aggressive colora- 

 tion, which assists its possessors to capture their prey. It is the direct opposite to 

 protective coloration; may be such as to aid an animal in stalking Its quarry, or it 

 may serve as a decog to attract the prey within reach of the animal pursuing. Jt is 

 evident that the bright crown patch of the kingbird can be of no service in con- 

 cealing the bird trom its insect food. Hence, by a process of exclusion we come 

 to regard the concealed crests of Fy-Catchers as alluring coloration. 



Of course, this reasoning is of little weight if taken alone. A much more im- 



iRudimentary organs or characters would at first sijrht seem to De an exception to 

 this rule: but rudimentKry organs are. in nearly all cases at least, regarded as rem- 

 nants of organs once functional and useful to their possessors. 



