Any animal (but especially any bird) that visits or resides in a specified location during the winter(noun)
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Use "winterer" in a sentence
"'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."
"A more desolate existence than the life of a fur-trading winterer in the far north can scarcely be imagined."
"Such temerity amazed the winterer beyond coherent expression."