Geographic variation in White-eared Hummingbird is weak and clinal (Pyle 1997; see also Dickey and van Rossem 1938); three subspecies usually recognized:
borealis, described as Hylocharis leucotis borealis Griscom 1929; type locality Pinos Altos, Chihuahua, Mexico
Occurs in southen Arizona, United States, and in northern Mexico in Sonora, Chihuahua, and Tamaulipas.
Subspecies borealis is similar to nominate leucotis but "larger, the underparts much more extensively white, with less greesnish, grayish or bronzy edgings and tips to the feathers in both sexes" (Griscom 1929).
leucotis, described as Trochilus leucotis Vieillot 1818; type locality Brazil, error, Orizaba, Veracruz, Mexico designated as the type locality by Griscom 1929
Occurs in central and southern Mexico and in Guatemala.
See Detailed Description.
pygmaea, described as Basilinna leucotis pygmaea Simon and Hellmayr 1908; type locality Matagalpa, Nicaragua
Occurs in El Salvador, Honduras, and Nicaragua.
Subspecies pygmaea is similar to nominate leucotis, but is smaller, with a reduced green gorget, and the underparts are more heavily mixed with white (Simon and Hellmaur 1908).
Phylogenetic analysis of DNA sequence data reveals that hummingbirds (Trochilidae) constitute nine major clades, comprising the hermits, mangos, Patagona, topazes, coquettes, brilliants, mountain-gems, bees, and emeralds (McGuire et al. 2014). Hylocharis leucotis is a member of the emerald clade. Other genera that are documented to belong to the emerald clade are Cynanthus, Chlorostilbon, Cyanophaia, Klais, Orthorhynchus, Stephanoxis, Campylopterus, Abeillia, Chalybura, Thalurania, Phaeochroa, Leucippus, Eupherusa, Microchera, Elvira, Goethalsia, Goldmania, Aphantochroa, Taphrospilus, Eupetomena, Trochilus, Leucochloris, Amazilia, Chrysuronia, Hylocharis, Lepidopyga, and Damophila (McGuire et al. 2014).
Hylocharis leucotis long has been suspected to be most closely related to Hylocharis xantusii (Xantus's Hummingbird) of Baja California (Mayr and Short 1970), which is confirmed by phylogenetic analysis of DNA sequence data (McGuire et al. 2014).
Hylocharis leucotis has hybridized with Selasphorus platycercus (Broad-tailed Hummingbird) (Howell 2002, Graves 2007).
The genus Hylocharis is polyphyletic (McGuire et al. 2014). The type species of Hylocharis is sapphirina (Rufous-throated Sapphire), which is not at all closely related to leucotis and xantusii. The proper generic name for these two species presumably is Basilinna (type species leucotis).