Bird feeders are a recent phenomenon in nature.  With the advent of naturalist field guides, due to the great work of Roger Troy Peterson, the population of bird watchers and bird lovers has steadily increased.  Bird feeders have made a difference, particularly to seed-eating birds, during the stressful time of winter and may have been a factor in extending the range of the cardinal in the north.  The cardinal is a non-migrant and needs all of the help it can get in winter. - Robert Bateman