508 PROCEEDINGS OF THE NATIONAL MUSEUM vol. io4 



Venezuela, on May 25, 1952, a date which corresponds with that 

 given by Cherrie as the breeding date for the same race in Costa 

 Rica (Zimmer, 1937, p. 6). 



The nest was found on the savanna, in a locality sparsely covered 

 with "chaparro" trees (Curatella americana L.). It was placed in 

 one of these trees, at the end of a branch, about four feet above the 

 ground. The nest was of bulky construction, approximately 15 

 cm. outside diameter, 6 cm. inside diameter, and 8 cm. deep, composed 

 of coarse grasses with many feathers woven into it, and lined with 

 slightly finer grasses. At the time of discovery, it contained three 

 well-feathered nestlings. 



Through the com^tesy of Mr. William Phelps, the junior author has 

 examined the magnificant collection of Venezuelan birds in the Colec- 

 cion Phelps at Caracas, Venezuela. Of the series of monachus, 

 collected throughout the year, the June specimens had enlarged 

 gonads. One immature specimen, taken in October at Cerro Upuima, 

 Bolivar, was so young it could almost be classified as a nestling. 

 This fact, in conjunction with the nestling skin of May 25, appears to 

 substantiate a breeding period of May through September. In 

 the same collection, M. tyrannus tyrannus is represented by skins from 

 May through October inclusive, with one immature specimen taken 

 in March. Thus, tyrannus is present in Venezuela, and in approxi- 

 mately the same habitat, during the breeding season of monachus. 

 Actuall}^, while both are bii-ds of the open country and are occasionally 

 encountered together, the concentrations of typical tyrannus in eastern 

 Venezuela are found in the vicinity of wooded country, whereas 

 monachus prefers the open short-grass savanna dotted here and there 

 with stunted "chaparro." As a rule, the flocks do not have an oppor- 

 tunity to mix with one another. . A perhaps extreme example of the 

 seasonal concentration of tyrannus occurs at Carpito, Monagas, 

 where the Creole Petroleum Corporation has established a large camp 

 in the lowland seasonal forest, with the resultant clearing of the 

 surrounding woods. This area, particularly the golf com-se, is 

 regularly visited by a large concentration of tyrannus, whereas 

 monachus has apparently not been able to invade the area. 



The race tyrannus is abundant locally on the northeastern[Venezuelan 

 plains from July through September, generally in flocks of 1,000 to 

 5,000 birds; in contrast monachus is rarely found in flocks of more 

 than 50 individuals. During this time the gonads of the adult 

 tyrannus are small, while those of monachus are enlarged. It is to 

 be noted that the young tyrannus arrive with the adults and form a 

 large percentage of the July concentrations. Zimmer (1937, p. 3), 

 speaking of the birds of Argentina and Paraguay, places the breeding 

 season as November through January. However, the collector be- 

 lieves the immature birds present in his region in July may be younger 



