During the short winter days birds such as Blue Tit's can spend most of daylight feeding just to survive. By feeding sunflower hearts the time spent cracking open the black sunflower husk is eliminated, enabling birds to save valuable time and feed more efficiently by giving garden birds maximum energy with minimum effort.
A huge range of garden birds favor sunflower hearts, even birds which are normally non seed-eating', such as Thrushes, Robins and Blackbirds who generally have difficulty in opening the outer husks.