This small owl is a permanent resident from the southwestern United States to southern South America, occurring in tropical, subtropical, and cold temperate lowlands (sea level to 1,400 m in the United States and Mexico; to 1,900 m in Central America). It occupies a wide variety of ecosystems, from semiarid desert scrub to lush tropical rain forest. Pairs typically nest in cavities excavated by woodpeckers, or those formed by limb decay, less often in forks or depressions in trees. In the United States, this owl inhabits live oak honey mesquite (Quercus virginiana-Prosopis glandulosa) woodlands, mesquite brush, and riparian areas of extreme southern Texas, and riparian woodlands and Sonoran desert scrub of south-central Arizona. In forested areas, nest sites are usually at the edges of clearings.
Ferruginous Pygmy-Owls are presumed monogamous, forming pairs during the fall of their first year after hatching, and nesting the following spring. Incubation and nestling development each last about 28 days. Females incubate 2–7 eggs, and both adults provide food for nestlings. Adults attend to fledglings until dispersal, 7–8 weeks after fledging.
An opportunistic predator, the Ferruginous Pygmy-Owl has a diet as diverse as its distribution, including insects, reptiles, amphibians, birds, and small mammals. Foraging rates peak during twilight hours, around sunrise and sunset. Because of its small size, long tail, and atypical diurnal and crepuscular behavior, the Ferruginous Pygmy-Owl may easily be mistaken for a passerine. When agitated, it perches with its tail cocked upward or jerks its tail up and down and from side to side.
From 1840 to 1991 this was the most collected species of owl in Mexico ( Enríquez-Rocha et al. 1993 ), and it may be the most common small owl in lowland areas of the American Tropics ( Oberholser 1974c ). At the northern extreme of its range in Arizona, however, it is considered scarce and listed as Endangered, even though formerly common there in cottonwood-mesquite (Populus-Prosopis) woodlands and forests, nesting in Gila Woodpecker (Melanerpes uropygialis) and Gilded Flicker (Colaptes chrysoides) cavities.
Until recent studies in Texas ( Proudfoot 1996 , Proudfoot and Beasom 1996 , Proudfoot and Radomski 1997 , Proudfoot et al. 1998 ) and Arizona ( Abbate et al. 1996 , W. Richardson pers. comm.), life-history information, especially breeding biology, was limited for this species. Current studies are addressing nest activity, nestling development, mortality, site fidelity, habitat requirements, and dispersal of young in Arizona and Texas.
To avoid reference redundancies, further information addressing research in Texas is by Proudfoot (GAP), unless other citations are given.