26 



BIRDS OF THE REPUBLIC OF PANAMA PART 4 



white; breast and lower undersurface much more heavily marked with 

 dusky, lacking pale area on sides of neck and forehead. Immature male 

 like female but with more blue sheen above and often on sides. 



Measurements. — Males (10 from Brazil, Argentina, and Uruguay), 

 wing 137.8-142.5 (139.9), tail 60.5-82.8 (73.7), culmen from base 

 12.2-15.4 (14.0), tarsus 15.4-17.8 (16.5) mm. 



Females (10 from Brazil, Paraguay, and Argentina), wing 132.0- 

 14.0 (135.2) tail 65.7-77.8 (71.2), culmen from base 12.0-15.4 (13.8), 

 tarsus 15.0-16.7 (16.0) mm. 



Casual; one definite occurrence in eastern San Bias. Breeds from 

 the highlands of Bolivia and Argentina south to Chubut; in the austral 

 winter regularly north to northern Brazil and Suriname. 



The single record for Panama is a specimen (in the University of 

 Michigan Museum of Zoology) from Obaldia (Puerto Obaldia), San 

 Bias, collected July 14, 1931, by Wedel, with sex marked " 2 ONE" 

 (apparently in error) . The bird is immature, with longer wing and tail 

 feathers much worn, in partial molt to adult stage. A few scattered 

 feathers on the left side of the crown above the eye, and others in the 

 tertials and wing coverts, are those of the dark blue male plumage. 

 Though on casual glance the specimen resembles the female sex, on 

 close scrutiny it appears to be a male beginning the change from juve- 

 nile dress to that of the adult. (For the record of this specimen, see 

 Eisenmann, Auk, 1959, pp. 528-532.) It is identified as elegans, as 

 would be expected. 



While Peters (Checkl. Birds World, vol. 9, 1960, p. 88, following 

 Hellmayr, 1935) includes this bird of eastern South America as con- 

 specific with Progne modesta of the Galapagos, the latter form in series 

 is much smaller, and also lacks the partly concealed white of sides and 

 flanks found in P. subis and P. elegans. Progne elegans here is given 

 separate specific status. 



The form murphyi, named by Chapman (Amer. Mus. Nov., no. 

 187, 1925, p. 6), from the coast of Peru, possibly may connect the two, 

 but this needs further checking (the Smithsonian at present has no 

 specimens) . 



There have been observations in June and July of 1958 and 1970 

 (Ridgely, 1976, p. 262) and on April 24, 1976 (Ridgely, in lift.) of all 

 dark Progne in central or eastern Panama, dates when the northern 

 migratory P. subis is very unlikely and when the southern migratory 

 P. elegans may well occur (see under P. subis). Although separation 

 of adult males in the field seems impracticable, females and immatures 

 are often distinguishable, and some reports of probable adult males of 



