FAMILY APODIDAE 229 



of swifts believed to be this species seen well at sea off Portobelo, 

 April 18, 1937. 



In my own observations, on April 22, 1949 at the Rio Mamoni 

 near Chepo, Panama, I saw 2 small flocks and killed 1 female. This 

 is the only specimen that I have collected, but from long familiarity 

 with the chimney swift in the north I have recorded flocks on other 

 occasions that I was satisfied were this species. These sight records 

 are as follows: April 13, 1947 on the Rio Jaque, Darien, about 20 

 passed to the north. In 1950, at the base of Cerro Chucanti, Panama, 

 several flew north over our camp in early morning on March 14. 

 Others were seen that season at Charco del Toro March 20 and 26, 

 and at Chiman April 1. In 1952 we noted flocks over the Rio Indio at 

 Chilar, Colon, March 7 and 8, and single birds at Isla Taboga March 

 15. 



CHAETURA VAUXI (Townsend) : Vaux's Swift, 

 Vencejo Oscuro Comun 



Figure 37 



Cypcelus Vauxi J. K. Townsend, Narr. Journ. Rocky Mountains, etc., 1839, 

 p. 348. (Fort Vancouver, Washington.) 



Size small ; brownish black on head, back, and wings, with rump 

 and upper tail coverts light to dark grayish brown ; throat and fore- 

 neck dull white. 



Description. — Length 105-110 mm. Adult (sexes alike), crown, 

 hindneck, back, and wings blackish brown, with a very faint greenish 

 gloss ; rump and upper tail coverts grayish brown ; lores deep black ; 

 throat and foreneck light brownish gray to grayish white; rest of 

 under surface grayish brown; under surface of wing somewhat 

 blacker. 



Immature, upper tail coverts tipped very narrowly with grayish 

 white. 



This is the most common of the small swifts in the western area of 

 the Pacific slope of Panama, seen regularly in rapid flight across the 

 sky. Over the towns they course high in air. Above pasturelands 

 and fields they often circle low, sometimes quartering like swallows 

 barely above the ground. As they pass they utter shrill chattering 

 calls, chee-ee chee-ee that have little carrying power, so that they are 

 heard only when the birds are near at hand. The common impression 

 of them is of their angular wings, often beating so rapidly that they 

 seem to blur as the birds pass. 



