The eastern meadowlark has a well-established breeding range from southern Ontario to New Brunswick, and south to northern South America. In the Kingston area, migrants return from the south by mid-March, and are turning south once more in mid-September to mid-October. The western meadowlark (Sturnella neglecta) looks awfully similar, and is best distinguished by its song and calls (Weir, 1989, pp.453-455). The western form entered Ontario in the early 20th century, but it remains a very rare spring and summer visitor this far east. In New York state (Levine, 1998, pp.547-548) the two species are noted in simlar manner to Ontario: ground nesters in fields and meadows, the meadowlarks are (like the boblink) susceptible to intensive farming practices.
At Presqu'ile provincial park, roughly 40 km to the south of us, the eastern meadowlark is a common migrant from mid-March to early May, and mid-September to early November. It is an uncommon summer resident. The most favourable nesting area in the park is the field at the Calf Pasture (LaForest, 1993, pp.371-372). In Peterborough county, to the northwest, the eastern meadowlark is a common summer resident, mostly gone south by the end of October, though some may linger into winter (Sadler, 1983, p.156). It is said that "the parent readily deserts the nest if disturbed".
The eastern meadowlark is known to breed widely across southern Ontario, whereas most reports of the western cousin lie west of Lake Simcoe (Cadman et al., 1987, pp.470-473). In the revised Bird Breeding Atlas (Cadman et al., 2007, pp.590-593) the situation seems little changed. Historically, the eastern meadowlark expanded into southern Ontario with the clearing of forests in the 19th century. By the early 20th century it was common in summer, as far north as southern Muskoka. It is especially common in the west to east belt from the southern shore of Georgian Bay, past Lake Simcoe and the Kawartha Lakes, to the St. Lawrence river valley. The region from Kingston west to southern Bruce county is said to be better suited to the nesting bird, because the region is less intensively farmed than the southwest, and the crops such as alfalfa and hay suit them better than the soybean and corn of the southwest (ibid., p.591).
References
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.
Levine,E (editor) (1998) Bull's Birds of New York State. Comstock Publishing Associates, Cornell University Press, revised version, 622pp.
Sadler,D (1983) Our Heritage of Birds: Peterborough County in the Kawarthas. Peterborough Field Naturalists / Orchid Press, Peterborough, ON, 192pp.
Weir,RD (1989) Birds of the Kingston Area. Quarry Press, 608pp. plus map.