[7][8] A study analyzing the genetic makeup of 12 Empidonax species found that the Alder and Willow Flycatcher are each other's closest relatives.

[10] The summer breeding range of the species covers most of Canada and Alaska, descending to a southernmost point in the northeastern United States.

In the summer breeding season, E. alnorum occupies wet, dense, shrubby thickets of alder (Alnus sp.

[3] During migration, the species occupies humid and semi-arid habitats, including forest edges and fields at elevations up to 2,500 ft (760 m).

Early successional scrubby vegetation or woodland edges are preferred habitats in winter, particularly those near water and below 1,100 ft (340 m).

The song is a distinct "fee-bee-o"; birds have been observed to throw their heads back and shake their tails while singing.

E. alnorum's diet is composed primarily of insects such as those from the Hymenoptera (sawflies, bees, wasps and ants), Coleoptera (beetles), Diptera (flies), Lepidoptera (butterflies and moths) and Orthoptera (locusts, grasshoppers and crickets) families.

[5] Nests are positioned low in bushes within shrubby thickets, and are cup-shaped, built loosely of vegetative materials such as grass, weeds, pieces of bark, and small twigs.

[11] Strips of grass or bark can often be seen dangling from the bottom of the nest, and the inside is lined with soft materials such as plant down.

As the species has not been extensively studied, courtship behavior is uncertain, but is believed to involve males chasing females through the trees.