In winter, when it warms up in the 40s-50s, I'll see flocks of "blackbirds" come into the marsh areas eating berries like dogwood, buckthorn, and buds on maples etc. They all look dark gray, black colored. But they sound just like robins. Ends up they are, thousands of them. SE Wisc, middle of Jan, Feb. Starlings and cedar waxwings will do the same, migrate up during warm spells, disappear for a time, then back again. It seems once the ground thaws, and they can get hold of nest materials and soft food, then they disperse all over and start nesting.