Last year was a good year for birding in Ontario, and 350 species were reported to ebird. There may have been a few other species that didn't make ebird since only a handful of Ontario's birders, perhaps half of the serious ones, post their sightings to this program. However I don't have access to last year's OBRC report, and ebird data are generally accurate, so I'll use that.
I had a particularly good year of birding in 2010, personally seeing 304 species in Ontario. As I mentioned in a previous post, I figure that I will have to see at least 16 genuine rarities (which I have labeled as codes 4-6), but probably 20 or more to break the record. Of the 304 species I saw, 14 of them were category 4-6 birds. They were:
Western Grebe - Point Pelee tip, May 13
White-faced Ibis - Amherstburg, May 1 and Windsor, May 6
Black Vulture - Dundas, March 20
Black-bellied Whistling Duck - Milford, July 25
Mississippi Kite - Point Pelee, May 15
Laughing Gull - Point Pelee, May 8 and May 10
Mew Gull - Niagara Falls, December 27
Chuck-wills-widow - Carden Plains, June 20
Scissor-tailed Flycatcher - Luther Marsh, August 7
Kirtland's Warbler - Point Pelee, May 22
Spotted Towhee - Long Point, December 3
Golden-crowned Sparrow - Ottawa, October 15
Blue Grosbeak - Rondeau, May 11
Painted Bunting - Kincardine, November 26
So basically, I could have broken the record IF I saw another couple of rarities, plus got all the category 1-3 birds. The reason why I only saw 304 species was because I never made it farther north than Algonquin, thus missing all the Rainy River specialties (Franklin's Gull, Yellow Rail, Le Conte's Sparrow, Black-billed Magpie, Western Meadowlark, Sharp-tailed Grouse, Western Kingbird), the Hudson Bay specialties (Arctic Tern, Smith's Longspur, Willow Ptarmigan, Common Eider), the stuff that Alan and Brandon saw at Netitishi (Black Guillemot, Dovekie, Sooty Shearwater, Gyrfalcon, A. Three-toed Woodpecker etc) plus some other odds and ends (Eurasian Wigeon, Barrow's Goldeneye, Gray Partridge, King Rail, A. Avocet, Red Knot, Western Sandpiper, Red Phalarope, Boreal Owl, N. Hawk Owl, Bohemian Waxwing, White-winged Crossbill). All the rarities I saw wouldn't have been missed if I have gone to Rainy River in early June, Netitishi for 2 weeks in early November, and Hudson's Bay in July. Both the Chuck and the Whistling-duck were long staying so I would have gotten them regardless.
There were a number of chaseable rarities which I could have easily gotten if I was trying to do a big year, such as:
Little Blue Heron - one present at Oshawa's Second Marsh May 9-13, also one present in Cornwall September 15-21
Glossy Ibis - one present at Hullett WMA from August 26-August 31
Lark Sparrow - several seen on Pelee Island - April 30 and May 19, plus some years one (or more) are on territory near Long Point
Gray-crowned Rosy-finch - one present in Marathon from February 12 - March 13 (quite the drive but definitely chaseable!)
I'm sure I am missing a few too. So basically, last year if I had gone all out, including trips to James Bay, Hudson's Bay, Rainy River, plus chased a bunch of rarities, I could have seen around 340 species of birds. It would have been a ton of effort, and there are a LOT of Ifs there. Just goes to show that it is possible!