Cackling Goose, Branta hutchinsii
The bird above is minima, the smallest subspecies; note the rounded head and absence of neck ring. The ones in the three pictures below are Aleutian (leucopareia) -- note the neck ring, slightly longer bill, and especially the blocky shape of the head.
Above, a Cackling Goose of the Aleutian subpecies; below, the same bird looks to be launching a David/Goliath sneak attack from the rear on a much bigger Canada Goose.
The bird shown above and below is a minima -- note the dark breast and underparts, as well as the small bill and absence of a neck ring.