There is no need to worry. Some America Robins migrate but if you look at the range map you’ll see that there are winter populations of Robins in most states year round. Robins are surprisingly hardy birds, capable of surviving temperatures well below zero. But that doesn’t mean sightings are common.
After nesting season has ended, they usually form large nomadic groups that roost at night in the woods. Their diet changes from mostly worms and insects to fruit, nuts and berries. I’ve seen them devouring our crab apples, Mountain Ash tree berries, and sometimes under my feeders looking for nuts. They also appreciate open water in the winter. If you have a pond or heated birdbath they may show up for afternoon drinks.
The Eastern Bluebirds also gathers in large family flocks at the end of nesting season and live more in the woods. They forage on fruit, nuts, and berries. If you have fruiting trees or bluebird feeders and a reliable source of water, you may host the bluebirds year-round.
With the lengthening of daylight the birds are becoming more active. Nesting season is just around the corner. Make sure your houses are ready and feeders and baths are full.