Mostly birds, and a few mammals. Almost anywhere that is anywhere near halfway between the equator and the poles has a lot of bird species that spend the winter. I go out birding almost every day and get quality photos almost every time, of a diverse palette of species.
In winter I tend to focus on the species that are ONLY available during the winter in this area. That means birds that spend the winter here, but migrate away as soon as February starts to turn into March. Sea ducks like Eiders and Long-tailed Ducks and Harlequin Ducks. Passerines like Nuthatches and Snow Buntings and White-throated Sparrows. Shorebirds like Sanderlings and Purple Sandpipers. Raptors like Eagles and Short-eared Owls. Large waterfowl like Swans and Snow Geese. Inland ducks like Green-winged Teal, Gadwall, and Northern Pintail.
There are so many species here in the winter that are not here at any other time, so winter is actually a really productive time to iNat. I suggest getting on eBird and checking your county there for recent locations and checklists, to see what is being seen currently right there where you live.
