“The northern cardinal (red cardinal or, Redbird) is a territorial song bird.
The male sings in a loud, clear whistle from the top of a tree or another high location to defend his territory.He will chase off other males entering his territory.
He may mistake his image on various reflective surfaces as an invading male,
and will fight his reflection relentlessly. . . .”
Image & info source: The birds and the bees and the flowers and the trees