You don’t need a bird-watching manual to identify these creatures. The snowbirds I know are humans.
The term snowbird is used to describe people in the colder climes of the U.S. and probably Canada who “migrate” to warmer weather when the show and cold comes on.
The snowbirds that are my friends go to Californa, Arizona or Texas. Mexico is, or was, a prime warm weather spot for the too.
Most of the snowbirds are retirees who have a second home/condo or a large RV to live in at hte secondary location.
Some say (urban myth?) that the term comes from the song “Snowbird” by Anne Murray.
In part, she sings: