of the face, chest, and nape vary among ten
subspecies of long-tailed weasel, Mustela frenata, proceeding
south (1) to central Mexico (5) [left column] and thence from
northern Mexico (6) to Oregon (10) [right column]. In tropical
of heavy rainfall [1 & 2] the pelage is darker and there is
a decrease in extent of the white
facial markings. In the more arid regions of central Mexico and
the Sonoran Desert [3 - 8], the pelage is lighter and the white
facial markings steadily more distinct. In the rain forests of
northern coastal California and Oregon, pelage again becomes
darker and facial markings less distinct.
suggested adaptive value of Gloger's
Rule is that the lighter colors reflect sunlight
and allow better thermoregulation in arid areas.