In my fairly urban yard, I typically get between 10 and 13 species (not always the same species), but if I hang out and watch the feeders for a couple of hours over the weekend, which I do regularly as part of Cornell's Project Feeder Watch, 12 species would be a good number for me, and I feel really lucky when I get 14 species. My all-time high species count for a weekend is 17. I think he said that his 18 species was since he started logging on January 8th or so...
My complete winter bird list (adding up all the species I've seen since logging for Cornell) is 34 species...I've denoted the regulars in
this color. Those are the birds that are most likely to make a regular appearance at my house...the others are more rare, or in some cases, I've only seen them once in many years.
American Crow
American Goldfinch
American Robin
Blue JayBrown Creeper (very rare)
Brown-headed Cowbird (very rare)
Carolina Chickadee
Carolina WrenCommon Grackle (very rare)
Cooper's Hawk
Dark-eyed Junco
Downy WoodpeckerEastern Towhee
European StarlingGolden-crowned Kinglet (very rare)
Hairy Woodpecker
House Finch
House Sparrow
Mourning DoveNorthern CardinalNorthern Flicker
Northern MockingbirdPileated Woodpecker
Red-bellied Woodpecker
Red-shouldered Hawk (very rare)
Red-tailed Hawk (very rare)
Rock PigeonRuby-crowned Kinglet (very rare)
Sharp-shinned Hawk (very rare)
Song SparrowTufted Titmouse
White-breasted Nuthatch
White-throated SparrowYellow-bellied Sapsucker (extremely rare)
That's only my winter backyard list; I don't bother logging birds I see during the summer. Even though I live in the heart of the city, it's part of the old city; a neighborhood of turn-of-the-century Victorian houses, with 100-year-old trees and plants and less of a focus on lawns, as in the suburbs.