VENEZUELAN ORNITHOLOGY — FRIEDMANN AND SMITH 509 



than the minimum of G months Zimmer's estimate would necessitate. 

 He bases this opinion on the general appearance of fresh-killed birds, 

 especially the appearance of the gape. Such a conclusion, if correct, 

 would lead one to suspect that the breeding season of the tyrannus 

 reaching Venezuela extends later than the season suggested by 

 Zimmer, or that these migrants may be from a population breeding 

 much closer to the equator (perhaps the east coast of Brazil), a popula- 

 tion to which Zimmer has already drawn attention, or possibly even 

 from the upper Orinoco region of Venezuela. 



Thus, we have here an abundant species divided into extremely 

 similar continental races, and we find two races in the same area 

 during the breeding season of one. While Mayr (1942, pp. 199, 253) 

 states that this is of fairly common occurrence in birds, the only 

 examples he gives are of island races geographically isolated by 

 water. The possibility exists that the breeding ranges of these two 

 races are not geographically isolated, as we know of no effective barrier 

 between the ranges. On the other hand, we know of no zone of 

 integration, with intermediate populations. It is possible that at some 

 point between the now-known breeding ranges both may be breeding 

 races in the same area but during different months of the year, being 

 reproductively isolated one from the other principally by different 

 breeding seasons in the manner foreseen by Mayr (1942, page 199), 

 who states: "It is thinkable that a race, whose range extends from 

 the equator southward and which nests from September to November, 

 overlaps near the equator the range of another subspecies, whose 

 range extends from the equator northward and which breeds from 

 February to May. No definite cases are known, but Dr. Chapin tells 

 me that some indirect evidence points to its occurrence in two African 

 species." We may here have a similar case in South America. In this 

 connection, we point out that in the upper Orinoco region, near the 

 Venezuelan-Brazilian border, the two races are present together in 

 February and March (Friedmann, 1948, p. 500), and that in north- 

 eastern Venezuela during these months tyrannus is absent (or extremely 

 casual) arriving there in late June to early July. 



Even without direct breeding evidence, gonadal and plumage condi- 

 tion of additional specimens collected in southern Venezuela and north 

 to central Brazil should shed light on the breeding seasons and ranges 

 of these two races, and we look forward with interest to the findings 

 of future expeditions. 



Tyrannus nielancholicus chloronotus Berlepsch 



Tyrannus chloronotus Berlepsch, Ornis, vol. 14, 1907, p. 479 (Temax, Yucatdn). 



Inasmuch as this form presented no taxonomic problems, it was not 

 considered necessary to collect additional specimens. 



