120 PROCEEDINGS OF THE ACADEMY OF [1896. 



Certain wing feathers show a still more interesting phase of abra- 

 sion. In the Rose-breasted Grosbeak, as is well known, secondaries 

 and tertials in autumn and winter are marked on their edges with 

 spots of white (Plate V, figs. 7, 8), while in the Meadow Lark and 

 Curlews at the same season, many of the feathers have regular tooth- 

 like indentations of lighter color along the sides (Plate IV, figs. 8, 9). 

 By the time the breeding season has arrived these light-colored 

 areas have been completely lost, while the dark parts remain intact, 

 the line of demarcation having been followed as closely as if cut by a 

 pair of scissors, except that some curved lines become straight owing 

 to the whole barb breaking off beyond the light colored area (Plate 

 IV, fig. 9). In these feathers, both portions are equally pennaceous, 

 and do not exhibit any difference in structure, so that we must regard 

 the light portions as peculiarly brittle. It is a noticeable fact 

 that in all the birds that have been examined, the black feathers 

 or black parts of a feather seem less subject to abrasion than those 

 of any other color. 



In most cases where marked abrasion takes place, the lighter tips 

 serve to produce the blended appearance characteristic of the winter 

 plumage of all birds, while their loss brings out the strong contrast 

 of colors characteristic of the breeding season, and produced in 

 other species by actual molt. 



The case of the Bobolink is of particular interest in this con- 

 nection, diflTering from that of any other species, unless it be some 

 individuals of the Rose-breasted Grosbeak. It has a complete 

 spring molt, but instead of assuming the breeding plumage at this 

 time, as in the case of most birds which molt in the spring, it assumes 

 a dress almost as dull and blended as its winter attire, but which is 

 transformed to the breeding plumage by the abrasion of the long 

 buff tips which adorn all the feathers.' 



The utility of such a process is difficult to see. The long tips are 

 " acquired to be lost " as it were ; they begin to break off immediately 

 and within two months have disappeared. 



SEASONAL PLUMAGES. 



The number of recognizable plumages, which a bird may assume, 

 is obviously dependent upon the length of time that is required for 

 it to acquire the mature dress. The simplest case is where this is 

 accomplished when the first-plumage is molted or at the end of the 



' See Chapman, Auk, 1890, p. 120. 



