28o 



BIRDS OF THE REPUBLIC OF PANAMA PART 4 



In a banding study at Almirante, Rogers and Odum (Auk, 1966, p. 

 418) found that Chestnut-sided Warblers arriving there in fall had 

 exhausted their migratory fat reserves and had lost some weight from 

 the breast muscles. The fat-free weight of 20 was 6.8-9.1 (8.0) grams. 

 One collected by Strauch (Bull. Brit. Orn. Club, 1977, p. 64) weighed 

 10.2 g. 



Chestnut-sided Warblers {fide E. S. Morton) molt much ahead of 

 Bay-breasted Warblers, with which they often associate in Panama, 

 and by mid- or late March are already in full breeding plumage. They 

 are often seen with other passerines feeding on the fruit of the abun- 

 dant Miconia argentea. Usually a mixed feeding aggregation of paru- 

 lids will include only 1 Chestnut-sided Warbler. 



Eisenmann reports that birds seen in Panama usually carry the tail 

 diagonally cocked above the back, and sometimes jerk it nervously. 

 The wings are often carried drooped below the body. 



DENDROICA CASTANEA (Wilson): Bay-breasted Warbler, 

 Reinita Pechicastana 



Sylvia castanea Wilson, Amer. Orn., vol. 2, 1810, p. 97, pi. 14, fig. 4. (Pennsyl- 

 vania.) 



Small; upper surface green (grayish with brown crown in males 

 after February); undersurface buff, sometimes with brown on throat 

 and sides. 



Description.-— Length 111-130 mm. Male, September through Feb- 

 ruary, crown and upper back light yellowish olive, finely streaked with 

 black; lower back, rump, and upper tail coverts gray; wings black, with 

 lesser coverts tipped gray, middle and greater coverts tipped white, 

 forming two bars, remiges with inner web edged white, outer web of 

 primaries 9-4 edged gray, outer web of rest of remiges light yellowish 

 olive; rectrices black with large white spot on inner web of outer two 

 pairs; lores and orbital ring white; side of head light yellowish olive; 

 undersurface white, tinged buff, most heavily on abdomen and under- 

 tail coverts; flanks sometimes russet; underwing coverts white. 



Male, March and April, forecrown, side of head, including area all 

 around eye, and chin, black; hindcrown and nape russet; upper back 

 streaked black and warm buff; side of neck warm buff; throat, breast, 

 sides, and flanks russet; rest of undersurface buffy white; lower back, 

 rum]), wings, and tail as above. 



Female, like September-February male; in March and April some- 

 times with russet on crown, throat, and breast. 



Measurements. — Males (10 from Panama), wing 69.9-77.0 (73.7), 



