NATURAL SCIENCES OF THILADELPHIA. 45 



through the e3'es to and over the aurieulars. The blue mantle 

 onlj- parti}' appears at this time, being lightly washed over with 

 gray and clear brown ; the rectrices are heavil}^ dusky, as in 

 hirundo at the same season, but the dark color is on opi)osite 

 webs in the two species. The wing-feathers are new and perfect, 

 and more hoary-silvery than those of hirundo of the same age ; 

 but the pattern of coloration is exactly duplicated. The feet are 

 3'ellow, more or less obscured with dusky. 



Sterna antillarum. 



Summer resident, from early in April until October; and, except 

 at the height of the influx of the other kinds, the most abundant 

 tern of all. It breeds here in great numbers. Referring again 

 to an article in the American Naturalist for September, 18G9, for 

 an account of its nidification, I have onl}^ to add here — 



A tern shot Ma}^ 17, had then an Qgg ready to be laid ; but 

 most of the eggs are deposited towards June, and during the fore 

 part of that month. The first young birds I noticed were flying 

 June 20th; but this was early for them, the broods not being 

 fairl}- on wing until the middle of July. During all of May and 

 June, indeed, there are plenty of immature birds about; but 

 these, it should be observed, are of the last summer's broods, 

 rendering the conclusion obvious that at least two years are 

 required to assume the perfect dress. These birds have the bill 

 black, no black cap or white crescent, slaty aurieulars and occiput, 

 dark bar along the front edge of the wing, imperfectly colored 

 primaries, and slightly forked tail ; thus not possibly to be con- 

 founded with birds of the season, which are curiously variegated 

 with graj^-brown, and white, and show no pearly blue. The year- 

 lings were in plenty with the adults at the breeding-grounds ; but 

 whether or not they were paired and had eggs too, was plainly im- 

 possible to determine, as terns' eggs are almost never identified 

 as to the exact parent, when numbers of the birds are breed- 

 ing together. The usual number of eggs, I may repeat, is two, 

 not three, and often only one is laid ; they do not average over 

 1^ X 1 inch. The black tip of the bill of this species varies from 

 nothing to a fourth of the length of the bill. The distinctions 

 betw-een the species and S. minuta are constant and perfectly 

 satisfactory. 



18T1.] 



