Chapman — Variation in Ostinops Decuman us. 29 



ther study indicates that the variation in size in the male is apparently 

 attributable primarily to age, and that this fact must be given due con- 

 sideration in selecting material to determine the geographical variations 

 of the species in size. 



Variation with age. — In a series of seven males from Colombia, it was 

 found that in birds which appeared to be mature, the wing varied from 199 

 to 249, the tail from 167 to 210 mm. in length. Twelve Bolivian males 

 showed a corresponding variation of 199 to 245 and 157 to 193 mm., and 

 in eleven males from Chapada, Matto Grosso, these measurements were, 

 respectively, 195 to 239 and 156 to 188 mm. It appears that the varia- 

 tions in the length of the wing are due chiefly to the greater length of 

 the primaries, while those in the tail are mainly attributable to the greater 

 length of the yellow feathers. The wing variation is of a nature to create 

 a decided difference in the shape of the wing, the longer wings being 

 "pointed" with considerable difference in the relative length of the outer 

 primaries, the shorter wings being more "rounded" and with the outer 

 primaries more nearly equal in length. The difference between the two 

 types of wings would commonly be called generic in character. 



Although it is not usual to find such a pronounced variation between 

 first winter birds and those fully adult, it seems probable that the birds 

 with comparatively short wings and tail are first winter birds, those hav- 

 ing longer, pointed wings being mature birds. Furthermore, the fact 

 that both wings and tail in Ostinops are to some extent secondary sexual 

 characters, being used in the remarkable display which this bird makes 

 in the breeding season, may make them in a measure subject to such 

 variation in development as is shown by crests, ruffs, spurs and other 

 secondary sexual characters. 



The accompanying figures, illustrating the wings of birds from both 

 Colombia and Matto Grosso, make a detailed description of this variation 

 unnecessary, but attention may be called to the marked difference in the 

 width and outline of the outer web of the third and, especially, fourth 

 primaries (from without). 



Geographical Variation. — Using only material which appears to be 

 comparable as regards age, our series indicates that maximum size in 

 Ostinops decumanus, especially in the bill, is reached in the Paria Penin- 

 sula, of Venezuela; minimum size in the Province of Matto Grosso, Brazil, 

 where the culmen in seven birds averages 56.1 mm., as compared with 

 71 mm. in three birds from the Paria Peninsula. Colombia birds agree in 

 length of wing and tail with those from the Paria Peninsula, but specimens 

 from Chiriqui, at the northern limit of the bird's range, are somewhat 

 smaller. 



Males seem to show greater geographic, as well as greater individual 

 variation than females. The results of the study of our material may 

 be briefly summarized in the following : 



