122 



BIRDS OF THE REPUBLIC OF PANAMA PART 4 



grayish white, producing the effect of dark lower underparts with pale 

 and variable indistinct scalloped pattern. 



Immature, with pattern of markings of undersurface less distinct. 



Iris varying from dull mouse brown to reddish brown; bill, with 

 maxilla and distal third of mandible dull black; gape and lower half of 

 mandibular rami dull marguerite yellow in some; in others, bill dark 

 neutral gray; tarsus, toes, and claws dull neutral gray. 



Measurements. — Males (10 from Panama), wing 55.8-59.1 (57.7), 

 tail 17.9-20.7 (19.5), culmen from base 19.1-21.7 (20.1), tarsus 20.4- 

 23.5 (20.5) mm. 



Females (9 from Panama, with 1 from Costa Rica), wing 51.2-57.0 

 (54.1), tail 17.4-21.9 (19.5), culmen 18.0-21.7 (19.8, average of 9), 

 tarsus 21.2-23.8 (22.2) mm. 



Resident. Recorded in forested areas throughout the Republic from 

 Chiriqui to San Bias and Darien. 



F. G. Stiles (Wilson Bull. 1983, vol. 95, p. 169) argues persuasively 

 that M. philomela, ranging from southern Mexico to central Costa Rica, 

 is a species distinct from luscinia of southern Costa Rica and Panama 

 (and the South American populations treated as races of M. margina- 

 tus), readily separable by color in adults as well as by voice, as charac- 

 terized by Slud. Adults of luscinia can be distinguished from philomela 

 by grayish white throat and more mottled underparts. Stiles suggests 

 that until more is known of the relationship of luscinia to the South 

 American populations, and especially to the white-breasted M. margi- 

 natus (type from "Bogota," Colombia, presumably western Amazonia) 

 the population of southern Costa Rica and Panama be tentatively treated 

 as a species, M. luscinia, to be called Pale-throated Wren. Eisenmann 

 points out that the thin, whistled vocalization of luscinia is also given 

 by populations in western Colombia, northern Venezuela, Ecuador, and, 

 including white-breasted populations, in parts of Amazonian Peru, but 

 that in southeastern Peru (Madre de Dios) and adjacent Bolivia, a 

 musical song differing from those of both philomela and luscinia is 

 uttered (fide B. Coffey, Ridgely, J. Fitzpatrick) by white-breasted 

 birds, currently considered to belong to the same subspecies (margina- 

 tus) , that sing like luscinia farther north. 



As the luscinia song does not remotely suggest that of a nightingale 

 (nor does the bird look like that Palearctic bird) Eisenmann thinks 

 Whistler Wren might be a more useful name for the southern popu- 

 lations, reserving Nightingale Wren for M. philomela. 



These curious wrens are true forest inhabitants found from sea level 

 to high in the mountains, where there is suitable cover and reasonable 



