IOWA ACADEMY OF SCIENCES. 43 



The facts ascertained by this examination were briefly as follows: 



Out of sixty-one grenera examined, seventeen contained species characterized by 

 the possession of concealed crests, and forty-nine contained species without them. 

 That is about twenty-six per cent of the genera contained species with these 

 crests and seventy-four contained species without them. 



It has been held that these crests afforded a good generic character among the 

 TifrannUhx;, but the facts just given would militate against this view, a generic 

 character which fails six out of seventeen times being of very questionable value. 



To one acquainted with the North American Ti/rannidie only, there would seem 

 to be a relation between hirge sized birds and the possession of these crests. T;/- 

 rauvKS, Pitciiigiis, Milonlus and Mu'wdynestis are the largest of our Fly-Catchers, 

 and they all possess concealed crests, while the remaining N. A. genera (seven) 

 all comprise smaller birds none of which exhibit the crests. 



An examination of all the genera of the family, however, shows that this dis- 

 tinction breaks down almost completely, the average length of those species with 

 the crests being 6.5:1 in., and that of those without the crests being G.47 in., an en- 

 tirely insignificant difference which would be much reduced if the long-tailed 

 species of Milonlus were taken out of the first class. 



There is, as would be expected, a marked relation between the general color of 

 the birds and that of the crests. 



Thus out of seventeen genera with crests, thirteen had red or yellow crests as- 

 sociated with an absence of yellow in general color. Only two had red or yellow 

 crests associated with white in general coloration, and one of these, Milonlus, 

 showed red on the axillars. 



Thus we see that in sixteen out of seventeen cases, or 94 per cent, there is a 

 marked relation between the color of the concealed crests and the general colora- 

 tion of the birds. 



A condensed statement of the facts may be as follows : 



First — About 25 per cent of the genera of I'l/rannidce contain species possessing 

 concealed crests. 



Second — This crest has no reliable value as a generic character, holding good 

 in only two-thirds of the genera. 



Third — There is no relation between the size of the birds and the possession of 

 concealed crests if we take the whole family into account, although in North 

 America the largest species have crests, while the smaller have none. 



Fourth— There is an obvious relation between the color of the crests and the 

 general coloration of the bird, a large proportion of species with red and yellow 

 crests, having yellow as a main feature of their general coloration. 



Let us now attempt to explain the significance of concealed crests in the life of 

 the birds. Their frequent occurrence would indicate a priori that they are of ser- 

 vice to their possessors, and to point out that service is the main object of this 

 paper. 



In Vol V, page 396 of the proceedings of the U. S. National Museum is the first 

 suggestion of the significance of these concealed crests that I have been able to 

 find. It occurs in a report written by myself on a collection of birds from 

 Nicaragua. 



In discussing Muscivora mexicana, a species of Fly-Catcher with a marvelous 

 fan-shaped, erectile crest, the following language is used: 



"Is it not possible that this bird is provided with its remarkable crest for the 

 purpose of attracting its insect prey, and that the slow and regular waving motion 



