202 On the so-called Sterna Portlandica. 



the eighth bird we find the tarsi and feet clear, bright coral, 

 the bill black, with the lower mandible dull red as far out as 

 the gonys. Through this series of eight specimens there 

 runs but little variation of plumage, excepting that the in- 

 creasing reddishness of the tarsi and bill is regularly corre- 

 lated with a whiter shade in the color of the rump and upper 

 surface of tail, and a gradual decadence of the dark bar on 

 the wing, which mark, well known to indicate immaturity, 

 is altogether wanting in the last specimen. 



We now pick up a tern of a still more advanced stage. 

 The white of the forehead is encroached upon^and narrowed 

 down by the black of the crown, the tarsi and feet are coral 

 without any tinge of duskiness, the bill is bright, clear, red 

 as far out as the angle of the gonys on both mandibles, and 

 the rump is now for the first time entirely white. From this 

 specimen we find an easy and complete transition through 

 birds with redder and still redder bills and white foreheads 

 spotted and blotched with black, up to the typical, adult 

 Sterna hirundo, with its black cap and red bill simply tipped 

 Avith black; A more complete and perfect series could not 

 be desired than that we have before us connecting the bird 

 first described with the typical Sterna hirundo. Let us 

 compare this same black billed, black legged hirundo with 

 our specimen of Sterna Portlandica, taken at Muskegat 

 Island, July 1st, 1870. 



The two birds placed side by side, a careless observer 

 would sa}' at once they are the same, and indeed the general 

 effect is surprisingly similar. The pattern of the head is 

 precisely identical, the under parts in both are pure white, 

 the mantle dark pearly ash, and the cubital bar nearly equal 

 in color and extent. But the rump of Portlandica is 

 emphatically white in decided contrast with the ashy one of 

 the other bird, and upon comparing the shape and propor- 

 tions of the tarsi, feet, bill, etc., the two in this respect, are 

 found to differ irreconcilably. Evidently S. Portlandica is 

 not to be confounded with the bird we have been studying. 



