No. 573] 



PATTERN DEVELOPMENT 



feathers that disappear when the tail is shut. This points 

 to the conclusion that the development of a white mark 

 which is ever conspicuous is allowed in nature in such 

 cases only where it may be no detriment to the species 

 through rendering it too conspicuous by contrast. Thus 

 the bald eagle or the black-backed gull have nothing to 

 fear from such a banner mark. For small weak-flying 

 birds, however, the case may well be different. Yet even 

 these often show much white and I believe that it would 

 be possible for a species in its phylogeny to develop more 

 and more white if at the same time its habits of watchful- 

 ness or other actions developed equally to counteract any 

 disadvantageous result that might accompany the in- 

 crease. No doubt also a psychic factor is involved, com- 

 parable to what among ourselves we call "fashion." 

 Thus a change in action or dress which departs too far 

 from the accustomed appearance is apt to be disliked at 

 first, though in time it may if persisted in, be tolerated 

 and at length accepted. In the development of white 

 markings, for example in the feathers of the tail, it 

 seems likely that a series of small steps must have been 

 made rather than too great and sudden changes. So in 

 the rock pigeon the white of the tail is limited to the outer 

 vane of the outer tail feather. In the turtle dove the 

 outer vane of the outer feather, and the entire tips of the 

 four outer feathers are white. The next step would be 

 to develop an entirely white outer feather and then two 

 (as in the passenger pigeon) and so on. In the sparrows 

 similar steps are shown by the lark sparrow (Chon- 

 destes) in which the tips only of the outer feathers are 

 white, the bay-winged bunting which has practically all 

 the outer feather white, and a little of the tip of the 

 second, the junco with two outer feathers and part of a 

 third white. No doubt steps such as these must have been 

 passed through by many white-tailed species. 



It is difficult to say how disagreeable to their normally 

 colored neighbors, albino birds may be. I have seen an 

 albino robin in the fall of the year with a flock of other 



