FAMILY TYRANNIDAE 489 



tail 50.9-56.5 (52.9). culmen from base 13.3-14.8 (14.1), tarsus 

 17.7-18.6 (18.0) mm. 



Females (10 from Panama), wing 59.0-62.4 (60.3), tail 48.0-54.8 

 (50.2), culmen from base 13.0-14.2 (13.5), tarsus 16.0-17.2 

 (16.5) mm. 



Resident. Of irregular occurrence in forested areas of the Tropical 

 Zone, on the Pacific slope. Recorded from western Chiriqui from 

 near the Costa Rican boundary (Puerto Armuelles) east along the 

 base of the volcano (Bugaba, Divala), and to 1200 meters elevation 

 (Sereno) near the boundary with Costa Rica; along the mountains 

 in Veraguas (Calobre, Santa Fe) ; on Cerro Campana ; Cerro Azul 

 and Cerro Chucanti, eastern Province of Panama; in eastern Darien 

 from Garachine. the lower Sambii Valley, and the slopes of Cerro 

 Pirre and Cerro Tacarcuna to Jaque. On the Caribbean slope re- 

 corded on the upper Rio Changuena, Bocas del Toro ; Calovevora in 

 northern Veraguas ; El Uracillo, northern Code ; and the lower 

 Rio Chagres drainage (including the northern Canal Zone), eastward 

 through the Comarca de San Bias to the Colombian boundary. 



While found frequently in company with Myiobiits atricaudus, it 

 is more restricted in distribution, seeming to be less common both 

 in the drier regions of the Pacific slope, and the wetter ones of the 

 Caribbean side, in the area west of the Canal Zone. 



These are active birds, often associated with moving groups of 

 other small forest species, usually as single individuals, and not with 

 others of its own kind. In its almost constant movements, it spreads 

 the tail and often droops the wings as it moves quickly through 

 trees and undergrowth. In this it is as active as any warbler. Its 

 food is small insects, taken on leaves or in the air. The only calls 

 that I have heard from it are sharply uttered chipping notes. Skutch, 

 in a detailed account of the species (Pac. Coast Avif., no. 34, 1960, 

 pp. 539-551), rarely recorded it giving a low song of several repeated 

 notes. In southwestern Costa Rica he reported two aberrant, ap- 

 parently partially melanistic individuals in which the sides of the 

 breast were black. 



The birds, as stated, ordinarily range alone, rarely associated in 

 pairs. Nest construction and care of the young are duties of the 

 female alone. The closed nest is attached to the tip of a pendant 

 branch, swinging free in some small open area, often above a forest 

 stream, from 2 or less to 6 or more meters above base level. In 

 Skutch's observations the bird began by attaching fibers as a tuft at the 

 end of the supporting branch or vine. As work progressed the "lower 



