Empidonax, Cabanis, Journal für Ornithologie, III, Nov. 1855, 480. (Type, Tyrannula pusilla.) Tyrannula of most authors.
Empidonax acadicus.
1225
Gen. Char. Tarsus lengthened, considerably longer than the bill, and exceeding the middle toe, which is decidedly longer than the hind toe. Bill variable. Tail very slightly forked, even, or rounded; a little shorter only than the wings, which are considerably rounded; the first primary much shorter than the fourth. Head moderately crested. Color olivaceous above, yellowish beneath; throat generally gray.
The lengthened tarsi, the short toes, the short and rounded wings, and the plain dull olivaceous of the plumage, readily distinguish the species of this genus from any other North American Flycatchers. The upper plates of the tarsi in a good many species do not encircle the outside, but meet there a row on the posterior face.
There are few species of North American birds more difficult to distinguish than the small Flycatchers, the characters, though constant, being very slight and almost inappreciable, except to a very acute observer.
The following synopsis may aid in distinguishing the species:—
Species and Varieties.
A. Inner webs of secondaries edged with pinkish-buff.
a. Olive-brown above, whitish beneath; tibiæ ochraceous.