KV 



Vol. XXIX, pp. 71-72 April 4, 1916 



PROCEEDINGS 



OF THE 



BIOLOGICAL SOCIETY OF WASHINGTON 



DESCRIPTION OF A NEW SUBSPECIES OF THE 

 AMERICAN LEAST TERN. 



BY EDGAR A. MEARNS. 



The least tern, Sterna antillarum (Lesson) was described from 

 Guadeloupe Island, West Indies, in the year 1847. The Pacific 

 Coast form has apparently never been recognized and is here 

 described as follows : 



sterna antillarum browni new subspecies. 



BROWN'S TERN. 



Type- specimen. — Adult male, Cat. No. 134,773, U. S. Nat. Mus. ; col- 

 lected on its breeding-ground, near Monument No. 258, Mexican 

 Boundary Line, on the edge of the Pacific Ocean, in San Diego County, 

 California, July 12, 1894, by Edgar A. Mearns. (Original number, 

 11,259.) 



Suhspecific characters. — Slightly smaller than Sterna antillarum antil- 

 larum (Lesson), from which it also differs as follows: Black of crown 

 prolonged backward in an occipital crest which occupies the middle of 

 the upper neck ; three outer primaries usually black except on the inner 

 border of their inner webs ; upper parts darker gray ; under parts more 

 grayish (less pure white) ; bill usually more narrowly tipped with black, 

 often without any. 



Measurements. — Type (taken by the author from the fresh specimen). 

 — Length, 228 mm.; alar expanse, 522; wing, 181; tail, 78; culmen 

 (chord), 29.5; tarsus, 16; middle toe, together with its claw, 16. Average 

 measurements of three adult male topotypes (skins). — Wing, 166; tail, 

 75.7; culmen, 28.2; tarsus, 14.3; middle toe, 12.2. Averages of two 

 adult female topotypes (skins). — Wing, 166.2; tail, 75; culuien, 24.5; 

 tarsus, 14; middle toe, 11.5. 



Measurements of Sterna antillarum antillarum (Lesson). — Averages of 

 nine adult males from the Atlantic shores of tlie United States (skins). — 

 Wing, 168.1; tail, 82; culmen, 28.8; tarsus, 14.6; middle toe, 12.9. 

 Averages of ten adult females from the Atlantic coast of the United 



14— Proc. Biol. Soc. Wash., Vol. XXIX. 1916. (71) 



