n. Any animal (but especially any bird) that visits or resides in a specified location during the winter
The Century Dictionary and Cyclopedia
n. One who or that which passes the winter in a specified place or manner; specifically, an ox or cow kept to feed in a particular place during winter.
Word Usage
"'winter bird,' or 'winterer' -- I suppose, because it is one of the few that stay in these parts all the year round, and is therefore often noticed by them in winter time."