Robins can subsist on a diet of berries and other organic vegetation reasonably well providing that they can find water and shelter from cold.
Most birds that regularly winter in New England are well suited to withstand cold temperatures. In the fall, many birds grow additional feathers for insulation. To keep warm while roosting, birds fluff their feathers. Because of the way their feathers are layered, this behavior traps pockets of warm air next to the skin.