FAMILY FORMICARIIDAE 225 



white, the light color partly evident in center ; cheeks and malar 

 region dull black. 



These are birds of the forest undergrowth, most common in the 

 lowlands and lower hills from central Panama eastward. Their 

 life history has been described by Dr. Edwin O. Willis whose de- 

 tailed report, The Behavior of Bicolored Antbirds (Univ. Cal. Publ. 

 Zool., vol. 79, 1967, pp. 1-127, 3 pis., 21 figs.), covers many months 

 of observation in Costa Rica, Panama, and northwestern Colombia. 



Zimmer in a review of these birds in Peru (Amer. Mus. Nov., no. 

 917, 1937, p. 5) combined two groups of generally similar appearance, 

 viz., bicolor and leiicaspis under the latter name, an action accepted 

 by Peters (Check-list Birds World, vol. 7, 1951, pp. 247-248) and 

 currently in general use. Willis points out (cit. supra, p. 3) that if this 

 course is followed there should be a further combination with another 

 similar group, rufigula, which is brown underneath. In another state- 

 ment, Willis (Condor, 1968, p. 128) prefers to treat them as three 

 separate species, a course that appears appropriate on existing evi- 

 dence. The subspecies united under the specific name bicolor have 

 the central under surface pure white, with the side of the head on 

 cheeks, malar, and anterior-auricular regions black. The females 

 have the center of the back plain brown. The leiicaspis group of 

 forms also are white on the under surface but include in this color 

 the side of the head. They also have a black superciliary. The 

 females have a large area of cinnamon-rufous partly hidden by the 

 longer feather tips in the center of the back, that would be prominent 

 in display. 



The bicolor group as here accepted, ranges from the Caribbean slope 

 of Honduras and Nicaragua, in Costa Rica also on the Pacific side, 

 and continues in Panama and Colombia to western Ecuador. Two 

 subspecies are found in Panama. 



GYMNOPITHYS BICOLOR OLIVASCENS (Ridgway) 



Pithys bicolor olivascens Ridgway, Proc. U.S. Nat. Mus., vol. 14, October 26, 

 1891, p. 469. (Santa Ana, Honduras.) 



Characters. — Forehead and side of head behind eye chestnut-brown 

 like the rest of the crown ; very slightly more olive on dorsal surface 

 when viewed in series. 



Measurements. — Males (10 from Chiriqui and Bocas del Toro), 

 wing 72.8-76.6 (74.8), tail 42.3^7.8 (45.1), culmen from base 

 19.1-20.2 (19.6, average of 9), tarsus 26.0-27.2 (26.4) mm. 



Females (10 from Chiriqui, Bocas del Toro, and Costa Rica), 



