The northern cardinal is a permanent resident in most of southern Minnesota, and a few make their homes in the north. This year, a very few were heard singing the rich whistled "what-cheer, cheer, cheer" song in January, but now in mid-February this sound is commonly heard. There are many variations of the song. Both sexes sing, and sometimes together. These are territorial songs.
So the very early start of the nesting season is marked by renewed singing, and at feeding stations we will notice mate-feeding now in late winter. The male often feeds the female, a courtship gesture. This is also the time when a cardinal starts to respond to its reflections in a window, displaying and attempting to drive away a bird it thinks is an intruder. I have seen both sexes do this.
Mobiles hung from an eave or sun-reflecting ribbon tape can help break up these flights.