FAMILY PARULIDAE 



28l 



tail 48.0-55.1 (52.2), oilmen from base 11.1-12.1 (11.6), tarsus 17.7- 

 19.0 (18.2) mm. 



Females (10 from Panama), wing 65.0-75.1 (69.7), tail 47.0-53.8 

 (50.0), culmen from base 10.3-12.8 (11.6), tarsus 16.0-18.7 (17.1) 

 mm. 



Migrant and winter visitor from the north. Common. Found on the 

 Pacific slope from eastern Veraguas, the mountain area of Code (El 

 Valle), and western Province of Panama (Cerro Campana) eastward, 

 being especially common in the Bayano River Valley of eastern Pan- 

 ama Province and in Darien; it has not been recorded from Chiriqui. 

 On the Caribbean side it ranges throughout the Republic from western 

 Bocas del Toro to eastern San Bias. Mainly found in the Tropical 

 Zone, it is recorded in the lower edge of the Subtropical Zone at El 

 Valle, and on Cerro Campana. In the Perlas group it has been recorded 

 from the islands of San Jose, Isla del Rey, and Saboga. 



The first Bay-breasted Warblers arrive in Panama in mid- September 

 (Ridgely, 1976, p. 297), although few are seen before October. Molt 

 of adults takes place in March; immature birds seem to molt slightly 

 later. By April, numbers of Bay-breasted Warblers have decreased in 

 Panama. The latest date for which the species is recorded in Panama 

 is May 1, when in 1969 G. Tudor saw 1 at Cerro Azul, Province of 

 Panama. On March 18 and 19, 1957, I found a considerable migration 

 through the forest along the lower Rio Oria west of the southeastern 

 tip of the Azuero Peninsula. While D. Hicks netted this species almost 

 daily at Almirante, Bocas del Toro, during October 15-26, 1964, he 

 caught none there on the following spring migration (March through 

 April 1965), suggesting different routes on the southward and north- 

 ward flights (Eisenmann in litt.). N. G. Smith reports seeing one at 

 Almirante during the "last week of March" 1965. 



The Bay-breasted Warbler is the commonest wintering warbler in 

 the forests of central Panama, especially on the Caribbean slope. Its 

 numbers are often underestimated, as the birds are usually in forest 

 canopy or high in woodland and easily overlooked. Central and eastern 

 Panama are the centers of its notably small wintering range. Its popu- 

 lation may have increased in the 1970's in response to spruce bud- worm 

 outbreaks in its breeding area. In Panama it feeds largely on the fruit 

 of Miconia argentea and of Bursera, two common small trees. Ridgely 

 {in litt.) estimated 60 Bay-breasted Warblers on the Achiote Road, 

 Canal Zone, March 18, 1980, and 50 at Ft. Sherman the next day. 



A male collected by Strauch (Bull. Brit. Orn. Club, 1977, p. 64) in 

 Province of Panama (location not given) weighed 11.4 g. 



