FAMILY SYLVIIDAE 



187 



central whitish streak more or less present; flank feathers olive-brown, 

 fluffy, decomposed; undertail coverts whitish. 



This species, sometimes called the Half-collared Gnatwren, is found 

 from Nicaragua to southern Peru. In Panama, where two subspecies 

 occur, it is an uncommon and little seen denizen of thick undergrowth 

 in humid forest in lowlands and hill country to perhaps 1000 m. Usually 

 found in pairs or small family groups, its behavior is wrenlike. It hops 

 actively from log to vine to twig, often clinging sideways, holding the 

 tail almost at a right angle and habitually jerking or flicking it. Ordi- 

 narily, it keeps low, not far above the undergrowth, but Ridgely re- 

 ports seeing pairs foraging 5 to 7 m above the ground. 



The gnatwren's diet is almost purely animal matter gleaned from 

 plant stems and foliage or picked from the ground; sometimes it tem- 

 porarily joins a mixed band of small birds following army ants. E. A. 

 Goldman noted the stomach contents of 2 collected at Portobelo, Colon, 

 in May 1911 : both had full stomachs, one containing arachnid remains 

 20%, bits of a bug 10%, ant remains 60%, moth remains 10%, the 

 other with a spider 30%, 9 ants and 5 ant eggs 59%, another hy- 

 menopteran 2%, bits of a bug 5%, elytra of a nitidulid 3%, embryo of 

 a seed 1%. 



The gnatwren has a variety of calls suggesting a wren or an antbird, 

 but nothing that resembles a territorial advertisement song. Ridgely 

 (1976, p. 280) says the usual call is "a fast chattering chrichrichrich- 

 richri" and Slud (Bull. Amer. Mus. Nat. Hist., vol. 128, 1964, p. 306) 

 lists "a 'woink, woink, woink,' usually followed by a chatter," "an 

 antbird-like whining nasal 'yeah,' " "an even 'peep' with the timbre of 

 an antbird or flycatcher," and several other sounds. Eisenmann re- 

 ports that birds mist-netted deep within humid forest at 1000 m on 

 Cerro Campana, after being caged gave a hissing ssssss. 



Olson (Proc. Biol. Soc. Wash., vol. 93, no. 1, 1980, pp. 68-74) has 

 recently revised the taxonomy of this species. His review did not af- 

 fect the nomenclature of any Panamanian populations. 



MICROBATES CINEREIVENTRIS SEMITORQUATUS (Lawrence) 



Ramphocaenus semitorquatus Lawrence, 1862, Ann. Lyc. Nat. Hist. New York, 

 7, p. 469. (Line of Panama Railroad.) 



Characters. — Belly darker gray with little if any whitish suffusion in 

 the middle; no postocular stripe. 



A male collected at the Peluca Hydrographic Station, Colon, on 

 February 24, 1961, had the iris dark wood brown; mandible pale 



