FAMILY SYLVIIDAE 



179 



Mus. Nat. Hist., vol. 7, 1937, p. 23). Riclgely notes that it occurs in 

 the elfin cloud forest on the wind-swept summit of Cerro Jefe (900- 

 1000 m), eastern Province of Panama, where few other lowland birds 

 occur. 



This species is an active searcher of foliage and twigs, moving rapidly 

 from branch to branch, constantly wagging or raising its tail to dif- 

 ferent angles. Usually encountered singly or in pairs, it often joins 

 mixed foraging flocks. The diet seems to be purely animal matter: 

 E. A. Goldman collected 2 at Cana, Darien, on May 26, 1912; the 

 stomach of one contained 2 pentatonid nymphs 37%, a large fulgorid 

 35%, an ant 8%, bit of caterpillar skin 10%, spider remains 10%; the 

 other contained a small caterpillar 25%, 2 small scarabaeids 20%, 3 

 curculionids (Cry ptorhynchini) 15%, a small chrysomelid 5%, a small 

 pentatonid 20%, homopteran remains 15%, bits of a spider with 2 or 

 more eggs 5%. One taken by Burton near Pacora, Province of Pan- 

 ama, weighed 5.9 g (Bull. Brit. Orn. Club, 1975, p. 85); 2 weighed by 

 Strauch (Bull. Brit. Orn. Club, 1977, p. 64) were 6.2 and 6.4 g. 



Figure 15. — Tropical Gnatcatcher, Cazajejen Tropical, Polioptila plumbea, 

 male (below), female (above). 



The vocal repertoire includes "a rather thin but musical song con- 

 sisting of a series of simple notes with decreasing intensity, sweet, weet, 

 weet, weet, weet, sometimes faster and sibilant; the usual call is a tzeet- 



