Birds in the genus Empidonax are notoriously hard to identify. Novel approaches to identification have been employed to try and increase the accuracy of species identification of mist-netted individuals, such as using ratios of and differences between the measured lengths of various body parts, including wings and beaks. Vocalizations are often relied upon for identification to species in the field when birds cannot be manipulated by hand.
The summer breeding range of the species covers most of Canada and Alaska, descending to a southernmost point in the northeastern United States. In autumn, E. alnorum migrates south through the eastern United States, Mexico and Central America, wintering in the western range of South America.
In the summer breeding season, E. alnorum occupies wet, dense, shrubby thickets of alder (Alnus sp.), maple (Acer sp.), and birch (Betula sp.) at elevations below 1,300 ft (400 m). During migration, the species occupies humid and semi-arid habitats, including forest edges and fields at elevations up to 2,500 ft (760 m).
(*Image from Wikipedia)