378 BIRDS OF THE REPUBLIC OF PANAMA PART 3 



The calls are rapid chipping notes, sometimes accompanied by a 

 metallic rattle that possibly may be made by the incised tips of the 

 outer primaries. 



These flycatchers, like their kingbird relatives, are aggressive, 

 usually toward birds on the wing, driving at hawks or turkey vultures 

 that chance to pass. Once I saw one pursuing a caracara that was 

 chasing an ani. While they are active flycatchers they also feed ex- 

 tensively on berries. Occasionally in an area of forest they may even 

 come to the upper twigs of a berry tree that rises into the tree crown. 



While Fork-tailed Flycatchers are present in the savanna area 

 throughout the year their numbers may vary widely. The subspecies 

 monachus ranges north through Central America to Veracruz and 

 the Yucatan Peninsula. In Mexico it is reported that the birds de- 

 crease appreciably in number at the end of July. And there is indica- 

 tion of movement among them in Panama in late August and Sep- 

 tember, apparently through migrants from the north, though this 

 needs verification by records through banding whenever these may be 

 available. Thus in the northern Canal Zone Eisenmann's notes cite 

 observations by J. E. Ambrose of numbers seen at Coco Solo from 

 August 24 to September 7, 1957. Eisenmann also on August 29, 1958, 

 noted 18 with 6 Eastern Kingbirds and 2 Gray Kingbirds resting 

 on a lawn at Fort Sherman, all giving the impression of passage 

 migrants. 



Locally, these birds are sometimes called Tijereta del Llano, or 

 fancifully, Golondrinas (swallows). 



On the Pacific slope they appear at times to occupy communal 

 roosts. Thus on March 18, 1955, at David, Chiriqui, toward sunset, 

 I recorded them singly or half a dozen together in straggling company 

 flying east past the grounds of the Hotel Internacional, 50 to 100 

 meters in the air, evidently toward some roost. I counted 200, and 

 then estimated that at least 500 passed during half an hour until the 

 sun was below the horizon. On January 23, 1963, in the open 

 savannas near the sea at Gago, Code Province, south of Rio Grande 

 on the highway. I recorded another large roost of these birds. As I 

 drove into this area at dawn about 200 came out of a small grove of 

 dense-leaved trees. They swirled past, twisting and turning in the 

 early morning breeze, so that occasionally the air seemed filled with 

 them. 



At the close of his interesting account of vocalization in kingbirds, 

 and their allies, W. John Smith (Publ. Nuttall Orn. Club, no. 6, 1966, 

 pp. 234-241) groups the 13 species that he studied in 2 subgenera. 



