Guatemalan Tyrannulet is a common and familiar small flycatcher of the highlands of southern Mexico, Guatemala, El Salvador, and possibly Belize. Like the (formerly conspecific) Mistletoe Tyrannulet (Zimmerius parvus), its diet includes a great deal of mistletoe berries as well as other fruits and insects. Guatemalan Tyrannulet is found inside humid montane forest, along forest edge, and in open and degraded forest. Guatemalan Tyrannulet is found at mid-elevation in this limited range, with some seasonal elevational migration. The wing markings are unique, with olive green coverts and remiges outlined in yellow (thicker on the leading edge of each feather), but lacking wing bars. Guatemalan Tyrannulet readily is detected by its plaintive pyeu call.