1S90.] Chapman, Changes of Plumage in the Bobolink. 12^ 



width .15 inch; the centre of the abdomen is still occupied by 

 leathers of the winter plumage, which arc faintly bordered with 

 yellowish; in the flanks still remain a few longitudinally striped 

 feathers of the winter dress, but these are being replaced by black 

 feathers terminally fringed similarly to those of the breast. 

 Allowing for the slight and unimportant changes a completion of 

 the moult will cause, it will be seen that we have here a bird 

 which, although it has acquired its final spring plumage as far as 

 feathers are concerned, still differs greatly from the black, yellow 

 and white Bobolink we are accustomed to see. My material for- 

 tunately illustrates the succeeding changes which occur before the 

 bird may be said to have gained its perfect nuptial dress. 



An examination of the brown- or yellow-tipped leathers shows 

 that their barbs are separated for at least their apical third, and 

 that the brown or yellow color commences at or near the point 

 of separation. Being thus without the mutual support furnished 

 by an interlocking of their delicate barbules, these fringe-like ter- 

 minations soon disappear before the constant wear and tear to 

 which they arc subjected. As we might suppose there is some 

 regularity in the manner in which succeeding parts of the bird's 

 plumage lose these terminal barbs, and they disappear first from 

 the more exposed portions and persist longest where they receive 

 the most protection. The head and breast, therefore, seem to lie 

 the first to become fully black, while the most perfect specimen 

 before me (one of several kindly loaned by Dr. A. K. Fisher) 

 still shows traces of yellow on the sides, flanks, and lower 

 abdomen. In the nuchal collar, scapulars, and rump abrasion is 

 evidently assisted by a fading of the more exposed portion of the 

 feather.* 



All these changes are closely correlated with a change in the 

 color of the bill. In the Corumba specimen it resembles that of 

 the fall and winter bird ; the mandible is reddish brown, the 

 maxilla flesh color. The final black first appears on the anterior 

 portion of the mandible and reaches its base before a similar 



*While the loss of these delicate terminations is largely effected by actual abrasion, 

 or even by the mere action of flying, it is evident that, losing their vitality, and lack- 

 ing protection, they become in a measure deciduous, and drop off without the assist- 

 ance rendered by a mechanical abrasion. The subject is an important one and de- 

 serving of more attention than has been accorded it. A similar change occurs in 



many other genera, for instance : Otoco/is, Agelaius, ScoUcophagus, Passerina, 



Junco, etc. 



