476 BIRDS OF THE REPUBLIC OF PANAMA PART 3 



ences in this coloration. Song with two syllables, usually written 

 fits-bew. 



Through its wide distribution in the breeding season to the south 

 of that of Empidonax alnormn, four geographic races have been 

 recognized in this species. All are migrant, moving south to live for 

 the period of northern winter in Central America and northern 

 South America. 



Like the related E. alnoriim, all have the complete annual molt 

 during the winter season, so that many of the migrant specimens 

 seen at that season are imperfect in color and plumage through wear 

 or the process of feather renewal. From this, identification of some 

 specimens to subspecies may be difficult or uncertain. Comparative 

 color differences of the forms are outlined in the accounts that follow. 

 Measurements cited have been taken from adult birds collected on or 

 near their northern nesting grounds. 



Gorski (Auk, 1969, pp. 745-747), in December and January of the 

 winter season of 1967-1968, used recordings of the two- and three- 

 syllabled songs, made on their northern nesting grounds, in playback 

 at several localities in central Panama. Response came from several 

 individuals to the two-syllabled "fitz-bew" of traillii, near Gamboa, 

 Canal Zone, and at La Jagua, near Pacora, eastern Province of 

 Panama. In many experiments there was no reaction to the three- 

 syllabled call of alnormn. During the mid-winter period the birds 

 appear to have local distribution as none responded at a number of 

 apparently favorable localities. 



As a group (including E. alnorum) these flycatchers are fairly 

 common in Panama through the Tropical Zone, with some ranging 

 higher in the lower Subtropical Zone. They are found mainly in 

 thickets and at the borders of forests, less often in undergrowth in 

 densely forested areas. While not especially shy, ordinarily they are 

 inconspicuous because of their quiet habits and the heavy cover in 

 which they live. Their usual call, heard occasionally, is a low whit, 

 with limited carrying power. 



Stomachs of those that I have examined have held insects only. I 

 have not seen them visiting berry-laden feeding trees. 



EMPIDONAX TRAILLII TRAILLII (Audubon) 



Muscicapa traillii Audubon, Birds Amer., Folio, vol. 1, 1828, p. 45 ; Orn. Biogr., 

 vol. 1, 1831, p. 236. (Arkansas Post, Arkansas County, Arkansas.) 



Darkest dorsally of the races ; more olive-brown above than 

 E. alnorum, with slight, if any, greenish hue. 



