When I was growing up, you didn't see them around. There also has been a dramatic increase in mockingbirds. A number of factors could figure into the rise of robins and certain other songbirds, Guthrie said. Global warming may be making winters milder. Abandoned farms are being overgrown with blackberries and buckthorn.
Suburban sprawl provides backyards filled with fruit-laden ornamental shrubs.
Birds that are expanding their ranges also seem to be getting hardier, Guthrie said. The population rebounds faster after a severe winter decimates the flocks. And there are more people counting birds, which means birds that might have been overlooked in years past are now being counted. Robins that weather the winter have a distinct advantage over the birds returning in early spring. The early bird may get the worm, but the one who never left gets the best nesting sites.