FAMILY TROGLODYTIDAE 



93 



Females (10 from Chiriqui and Costa Rica), wing 60.5-64.7 (62.4), 

 tail 41.7-47.5 (44.8), oilmen from base 19.2-20.8 (19.8), tarsus 22.4- 

 24.5 (23.2) mm. 



Resident. From present information, found locally in the lowlands 

 on the Pacific slope of northwestern Chiriqui from the lower Burica 

 Peninsula near Puerto Armuelles, to the northern base of the moun- 

 tains below and above Concepcion (Bugaba, Divala, Buenavista). 

 Thryothorns semibadius is a bird of limited distribution, found in Pan- 

 ama in southwestern Chiriqui from the lowlands of the Burica Penin- 

 sula near Puerto Armuelles to the base of the mountain area above 

 Concepcion. 



My first view of this bird in life came in early March 1960, when a 

 few were noted in thickets near the Rio Escarrea, at Buena Vista. In 

 February and early March 1966, they were fairly common near Puerto 

 Armuelles from the upper Rio San Bartolo, to the Rio Corotu near the 

 coast. Like other species of the genus, they ranged in pairs on or near 

 the ground in open thickets and in undergrowth in forest, usually near 

 water. Ridgely {in Htt. ) found two pairs in mangroves foraging on the 

 roots and in adjacent thickets, at Estero Rico, Chiriqui. Attention is 

 drawn to them by their low, chattering calls, and less commonly by 

 song, similar to that heard from various races of Thryothorus nigri- 

 capillus, but slightly higher pitched in sound. Pairs sing regularly in 

 antiphonal concert in which the leader, that I assumed to be the male, 

 is followed immediately by a lesser voice that I supposed is the female. 

 This sequence was clearly demonstrated when I moved quietly along 

 a woodland trail, with members of a pair a few feet away, one on the 

 right, the other on the left. With the onset of the full dry season at the 

 end of February, they sing less often. Because of this silence they are 

 seldom noticed in the dense cover that was their shelter. 



In southwestern Costa Rica, Skutch (Pac. Coast Avif. no. 34, 1960, 

 pp. 130-137) found it common in the valley of El General, often in 

 family groups of 3 or 4 birds. Throughout the year they slept in spe- 

 cially built nests in trees or bushes, usually near streams, sometimes 2 or 

 3 birds together, possibly a female with grown young, as he believed 

 that the mated pairs separated after nesting. The nests made in the 

 breeding season were near rapidly flowing streams. They were rounded 

 structures approximately 125x150 mm with an entrance chamber and 

 an inner compartment. The clutch was two, the eggs being "white with 

 fine, faint speckles of pale brown that are most numerous in a wreath 

 or cap on the thick end." Three eggs measured 20.6-22.2 by 15.1- 

 15.9 mm. The nesting season in Costa Rica extended from late De- 



