PASSERINE BIRDS OF NEW YORK 79 



modify wear. The longer a feather is exposed to the bleaching 

 of the elements and to the effects of mechanical abrasion, the 

 more ragged in appearance it becomes, and the older it is the 

 more rapid becomes its disintegration ; so that plumage showing 

 perhaps comparatively little wear during the winter, will rapidly 

 become tattered during the few months of the breeding season. 



Much of the abrasion is not due to external causes but to the 

 attrition of the feathers themselves one upon another. This may 

 be observed, for instance, upon the nape of the neck where from 

 the constant movements of the head the feathers become much 

 worn. The wing coverts, tertiaries and scapularies also show 

 markedly the effects of opening and closing the wings. The 

 feathers of the anterior parts of the body however seem to suffer 

 from contact with leaves and grasses while the bird is gathering 

 its food and the flight feathers of some species show marked 

 wear depending also of course upon their habits. It is in all of 

 these ways that position modifies wear. 



Another minor factor affecting wear and a very important one 

 is structure. The large strong remiges and rectrices by their 

 compactness, as well as the long-barbed abdominal feathers by 

 their yielding quality, both suffer less from abrasion than those 

 of intermediate weight and stiffness. The weaker feathers, too, 

 of young birds are peculiarly liable to abrasion, aided no doubt 

 by the clumsy efforts at locomotion of the birds themselves. 

 Even the remiges and rectrices are less resistant than those of 

 the adult, the borders being less compactly rounded out and the 

 pigment deficient. 



The color of a feather is another factor of considerable impor- 

 tance in determining^its wear, and it is well to bear in mind that 

 color may be due to pigment, to optical effects produced by 

 structural interference with rays of light or to a combination of 

 the two. As a matter of fact, black or iridescent feathers are 

 most resistant to wear, other things being equal, while certain 

 buffs and browns yield most rapidly. 



The pale contrasting borders and the paler areas of the 

 feathers of many species tend to decolorize and disintegrate as 

 far as the adjacent dark portions. There are many striking 



