On the so-called Sterna Porilandica. 205 



terns breed apart from the other species, and at Portland, 

 Me., whence the type specimen was obtained, Sterna macrura 

 is one of the most abundant terns. 



Now supposing the relationship of Porilandica to macrura 

 to be granted, as we consider that of our other black billed 

 tern to hirundo, to be proven, the question at once arises, 

 what is this peculiar condition of plumage, and how accounted 

 for? The young of hirundo and macrura are not described 

 as with black bill, tarsi and feet, in their first fall and winter 

 plumage, and assuredly these members cannot become darker 

 as the bird advances in age. Now strange as it may appear, 

 this is precisely the fact. With the special purpose of 

 obtaining information on this point, another expedition was 

 made to the breeding ground of the terns after the capture 

 of the black-billed birds in July and August, and a large 

 series of young and fall specimens of Sterna hirundo col- 

 lected, careful notes being taken on the color of the bill, 

 feet, etc., while the birds were freshly killed. The facts 

 elicited by a careful comparison of specimens are briefly as 

 follows. The color of the bill and feet in chicks a few days 

 old varies individually to a considerable extent, but in the 

 average the tarsi and feet are light, while on the bill, reddish 

 or orange-colored areas predominate over the dusky or black. 



In birds nearly or just able to fly the bill averages much 

 darker, in most instances the whole of the upper mandible 

 being black or dark brown with the exception of the maxil- 

 lary tomium, which is light, like the lower mandible. After 

 this period, as the bird advances in age the black area of the 

 bill spreads, the forehead whitens and the brown and gray 

 tipping of the feathers of the back wears off".* To this rule 

 there are, however, a few exceptions, some birds with a 

 nearly pure mantle and snow white forehead, having the 



* All the specimens of which we are now speaking are birds of the year, collected 

 in Sept. and Oct., but owing to the persistency with which their nests are broken up by 

 the eggers, their ages are various, several taken at the latter date being scarcely able 

 to fly. 



