"It is thought that Anna's Hummingbirds are able to winter so far north because their diets contain a larger proportion
of insects and arachnids than most hummingbirds.
Not only do these bugs provide nutrients during the winter when there are no flowers blooming, but they also
provide a slower metabolizing source of food which may help them survive the long nights.
Anna's Hummingbirds also have a fairly large body weight for a hummingbird which may also help them. But they do live a precarious existence
in the winter and the presence of hummingbird feeders has probably also helped to encourage their northward expansion."