Just a couple days ago an American Robin (Turdus migratorius) stopped by for a drink at the bird bath here at my cabin. It’s not at all unusual to see Robins here during any month of the year, even during winter.
During the summer earthworms, snails, spiders and other arthropods make up much of their diet. They change their habits when the seasons change.
Yes, some Robins do migrate, but many also roam from place to place in large groups looking for their winter meals, not necessarily heading south to warmer weather. Often I’ll see many Robins and Cedar Waxwings (Bombycilla cedrorum) together enjoying berries of Eastern Red Cedar (Juniperus virginiana). They’re on the lookout for other fruits and berries too, of hollies, crabapples, hawthorns, and others.
Don’t think, when you see Robins in the middle of winter that spring is on its way. Spring will arrive on its own schedule and it has nothing to do with Robins.