CHICAGO (CBS) — A birdwatcher with 30 years behind the binoculars says birders are seeing incredible numbers of seldom seen birds in suburban backyards.

Tim Joyce says he doesn’t know what’s happening, but he suspects there must be some deficit in northern pine forests which is cutting into the food supply available to birds.

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Joyce also manages two “Wildbird Unlimited” seed stores where he customers are telling him the same thing: unusually high numbers of unusual birds.

Joyce says he’s seen the first Evening Grosbeak in 30 years at his backyard bird feeder.

He says he’s seeing large numbers of hardy birds like Pine Siskins, Red Polls and Red Breasted Nuthatches, which often stay north.

Joyce says without several years of data, he wouldn’t say the high bird numbers are caused by global warming.

He says he just doesn’t know what’s going on other than to believe there’s some kind of food shortage driving birds south.

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