FAMILY PARULIDAE 



297 



Description. — Length 120-133 mm. Adult male, lores, forecrown, 

 orbital ring, and side of face black; top of crown and line from rear of 

 eye to nape, bordering black area, gray; hind crown and all of upper 

 surface, including tail and wing feathers except for primaries, bright 

 yellowish green; primaries dusky, with outer web edged bright yel- 

 lowish green; sides and flanks greenish yellow; rest of undersurface, 

 bend of wing, and underwing coverts bright yellow. 



Adult female, like male, but black replaced by gray, less extensive on 

 side of face. 



Immature, like female, but with gray areas replaced by warbler 

 green. 



Measurements. — Males (3 from Chiriqui), wing 58.1-61.5 (59.7), 

 tail 46.7-51.2 (49.5), oilmen from base 13.2-13.8 (13.6), tarsus 21.8- 

 22.6 (22.1) mm. 



Females (2 from Chiriqui), wing 57.1-57.2 (57.2), tail 47.6-49.6, 

 (48.6), culmen from base 13.7, tarsus 22.0-22.2 (22.1) mm. 



Resident. Found only in western Chiriqui in a few places around 

 Volcan at 1050 to 1350 m, and in immediately adjacent southwestern 

 Costa Rica, where it was first recorded by Skutch in 1964 (Publ. Nutt. 

 Orn. Club, no. 7, 1967, pp. 146-149). The Masked Yellowthroat in- 

 habits lush meadows and marshy areas near streams; at La Lagunita, 

 near El Volcan, I found a female perched in a spiny bush surrounded 

 by heavy grass near a stream — habitat that Geothlypis trichas might 

 choose. Although Griscom (Bull. Mus. Comp. Zool., vol. 78, 1935, p. 

 369) called this species "very rare" it is actually very local but not un- 

 common, usually found in loose colonies. Its voice is "a sweet twichee- 

 teeweeo tweecheo, repeated four or five times, then a pause before 

 starting again" (Ridgely, 1976, p. 301). In Costa Rica, Skutch (op. 

 cit.) found them most vocal during May and June. Ridgely (in litt.) 

 has heard them singing regularly in March in Chiriqui. 



On May 21, 1964, Skutch found a female working on a half-finished 

 nest near Canas Gordas, Costa Rica. When completed, 4 days later, 

 the nest was a bulky open cup composed of blades of lemon grass lined 

 with long, smooth, brown fibers of unknown origin, situated about 45 

 cm from the ground in a dense clump of lemon grass. The external 

 dimensions were 10.1 by 14 cm in diameter by 8.9 cm high. The in- 

 terior was 6.4 by 7.6 cm in diameter by 3.8 cm deep. The two eggs 

 in this nest were laid May 26 and 27; they were "white, spotted with 

 deep brown, pale brown, and pale lilac. The spots were largest and 

 most crowded on the thick end of the egg and diminished toward the 

 opposite pole, where they were few, small, and faint. The eggs mea- 



