The American crow is virtually unmistakable, and is often heard before it comes into view. The sightings are quite consistent from year to year, indicating a small overwintering populatrion, augmented by early migrants, harbingers of spring, peaking in March. Numbers are sparse from November to February, and - after that early spring peak - steady from May to October. Crows are opportunists, and part-time nest thieves, and so a lone crow or small flock is often mobbed by smaller birds defending their young, including red-winged blackbirds and grackles. Crows may in turn harass passing predators, such as red-tailed hawks. Crows are often seen singly, or in small groups of up to six birds. Occasionally a larger flock may be seen, presumed to be related to migration, e.g., 13 and 15 March 2005 (11-15 birds), 28 September 2014 (10 birds) and 31 October 2011 (21 crows). The old term for a flock of crows is a "murder", perhaps a reference to the discordant cries? The crow may also be found at sites along nearby Lake Ontario, such as Presqu'ile and Prince Edward Point.
In contrast, the common raven is a rare visitor to the limestone platform south of the Canadian shield, with just three sightings recorded here: 05 February 2000 (high over Crowe Bay), 01 August 2005 (west of Campbellford over Trout Creek) and 13 December 2017 (a pair seen overhead, also west of town, during a sudden cold snap). This largest of the crow family, like the grey jay, is found much more frequently just to the north, as along Eels Creek and in Petroglyphs Park, forested areas north of Stony Lake, some 50 km north of Campbellford, and further east in Tudor township. Wider districts where the raven is as common or more abundant than the crow include much of the Ottawa valley, and the Thunder Bay region north at least as far as the drainage of the Albany River.
At Presqu'ile provincial park, roughly 40 km to the south, the crow is a common migrant from mid-February to mid-April, and late September to mid-November. In contrast, the raven has but three records, between 4 September and 5 November (LaForest, 1993, pp.254-255).
In Peterborough county, to the northwest (Sadler, 1983, pp.114-115) small numbers of crows over-winter, and seasonal counts increase during February. The raven is an uncommon resident in northern Peterborough county and may migrate in small flocks.
The American crow is common across most of Ontario, except the far north, while the raven, as suggested above, is scarce south of the Canadian shield but widespread over most of the rest of the province (Cadman et al., 1987, pp.288-291). In the second edition of the provincial breeding bird atlas it is clear that the crow flourishes in agricultural and urban settings, while the raven generally breeds much further to the north (Cadman et al., 2007, pp.382-385).
Cadman,MD, Eagles,PFJ and Helleiner,FM (1987) Atlas of the Breeding Birds of Ontario. Federation of Ontario Naturalists and Long Point Bird Observatory, published by University of Waterloo Press, 617pp.
Cadman,MD, Sutherland,DA, Beck,GG, Lepage,D and Couturier,AR (editors) (2007) Atlas of the Breeding Birds of Ontario, 2001-2005. Bird Studies Canada, Environment Canada, Ontario Field Ornithologists, Ontario Ministry of Natural Resources, and Ontario Nature, 706pp.
LaForest,SM (1993) Birds of Presqu'ile Provincial Park. Friends of Presqu'ile Park / Ontario Ministry of Natural Resources, 436pp.
Sadler,D (1983) Our Heritage of Birds: Peterborough County in the Kawarthas. Peterborough Field Naturalists / Orchid Press, Peterborough, ON, 192pp.