We identified 3793 prey remains from 44 and 41 Mexican Spotted Owl (Strix o
ccidentalis lucida) territories in Arizona and New Mexico, respectively, fr
om 1991-95. We found no relationship between Mexican Spotted Owl reproducti
ve success and the proportion of dietary biomass comprised of white-footed
mice (Peromyscus spp.) or woodrats (Neotoma spp.). This was contrary to pre
viously observed diet patterns in Northern (S. o. caurina) and California S
potted Owls (S. o. occidentalis) showing that mammals can comprise 88.2% of
the dietary biomass in Arizona and 94.0% in New Mexico. We found that the
most important prey based on relative biomass for Mexican Spotted Owls were
woodrats (47.8%) and white-footed mice (17.0%). Gophers (Thomomys bottae)
and birds occurred more frequently in owl diets in Arizona, while rabbits (
Sylvilagus spp.), insects, and woodrats occurred more frequently in diets o
f New Mexico owls.