Of the three essentials for attracting birds, shelter, food and water--in winter food rises to the top of the list. After a long and bitter night, birds are at their lowest ebb and their stored calories are nearly gone.
During the daytime hours, the food consumed fuels a bird's high metabolic rate which produces the heat to keep him alive in the bitter cold of winter. Birds burn a tremendous supply of energy for their size. Keeping their body temperature near normal (100 – 112º F) requires huge amounts of calories, especially on those nights when it drops to below zero. They need to find quick food in the early hours of the morning.