BIRDS 



299 



the middle of the back, however, it expands greatly, forming a large 

 oval patch which extends posteriorly to the anterior part of the lumbo- 

 sacral region. Here the dorsal pteryla again contracts into a narrow 

 median band which extends along the middle of the rump to the oil 

 gland, expanding very slightly back of the acetabula. The ventral 

 tract forms anteriorly a single band along the upper and middle parts 

 of the ventral side of the neck. A little below the middle of the neck 

 it bifurcates and each half runs outward and posteriorly on the side 

 of the neck to the shoulder. Here it gives off laterally a shoulder 

 band which in turn divides into the alar and humeral tracts. The 

 main pteryla3 continue posteriorly on the sides of the breast. The 

 two diverge considerably, each becoming wider and extend along the 

 side of the abdomen to the knee. Here each contracts again and runs 

 down the front of the abdomen to near the anus, the two converging 

 once more. 



Color of the Bill. — The general development of the color of the 

 bill in the male is as follows : early in the life of the bird, in the be- 

 ginning of Stage II, both mandibles of the bill are yellow. Soon the 

 upper begins to become clouded with dusky, the yellow remaining 

 longest as a spot on the culmen generally near the tip of the mandible. 

 When the upper mandible has attained this coloration the lower be- 

 gins to become dusky, the dark color beginning at the tip and later 

 spreading over the whole mandible, the yellow remaining longest as a 

 spot on the gonys. The dark color of both mandibles is at first brown- 

 ish, later it becomes black. The color is developed in the same man- 

 ner on the bill of the female, but, the acquisition of the dark color 

 takes longer and the final tone is dusky-brown rather than black. 



The development of the black color on the bill and on the plumage 

 do not always progress at the same rate. Often birds may be found 

 with perfectly black plumage, but with the bill partly yellow ; the 

 lower mandible may be even entirely yellowish. In birds only partly 

 white below, the bill may be slaty-brown above and yellow below. 



Relationship between Color of Bill and Plumage., and Maturity. 

 — There is apparently no seasonal change of plumage in the males — 

 adults being equally black, whether taken in January, March or June. 

 The height of the nesting season is in March in most places. 



The following observations on the development of the color of the 

 plumage and bill are based on specimens taken at Tagus Cove, Eliza- 

 beth Bay and Iguana Cove, Albemarle, during the months of January, 

 February, March and June. We were not at the same locality any- 

 where else long enough to make observations on these points else- 



