The Niagara River flows 60 km from Lake Erie to Lake Ontario. In addition to being a major tourist destination, it provides drinking water, recreational fishing, employment, and electrical power to millions of people. The river is bordered by urban areas, industrial developments, and agricultural lands with parkland areas and remnant natural areas being interspersed. For a 15 km stretch downstream from the falls the river flows through a 100 m deep and 1 km wide gorge. The riverine habitats are quite varied, ranging from large lake-like areas, exposed boulder beds, rapids, falls, whirlpools, and stretches with swift currents. Within the gorge, the cliff rim, cliff face, and talus slope communities support one of the highest concentrations of rare plant species in Ontario.
The Niagara River annually supports one of the largest and most diverse concentrations of gulls in the world. More than 100,000 individuals can be observed foraging along the river during fall and early winter. A total of 19 gull species have been recorded (60% of all New World gull species), with up to 14 species being recorded on a single day. The number of gulls and diversity of species generally peak in November. Two species occur in globally significant numbers: Bonaparte's Gull and Herring Gull.
During fall and early winter 10,000 or more Bonaparte's Gulls can regularly be observed along the river (over 2% of global population). Peaks of more than 40,000 individuals have been observed on several occasions (1973, 1977, 1990, 1991) representing over 8% of the global population. Over the course of the fall and early winter season up to 100,000 birds have been estimated to pass through this site (over 20% of the global population).
Herring Gulls are also abundant; 20,000 or more individuals can be observed regularly with a maximum of 50,000 individuals being reported on a single day. This represents the regular occurrence of almost 6% of the North American Herring Gull population (ssp. smithsonianus) with upwards of 14% of the population being reported on a single day. The national threshold for Ring-billed Gulls is also regularly exceeded during spring migration.
Waterfowl concentrations during fall and winter also regularly exceed 20,000 individuals of more than 20 species. At least two species (Canvasbacks and Common Mergansers) are regularly present during late fall and early winter in numbers just above 1% of their estimated North American populations; Greater Scaup are occasionally present in significant numbers, and Common Goldeneyes are regularly present in numbers approaching the 1% threshold.
Due to the regional geography, large numbers of migrating raptors and landbirds cross the river during migration. Normally they do not stop in large numbers along the river corridor. Some specific sites along the river corridor are also significant for colonial nesters such as Black-crowned Night Herons, Common Terns, and Ring-billed Gulls.
BirdLife International (2019) Important Bird Areas factsheet: Niagara River Corridor. Downloaded from http://www.birdlife.org on 21/07/2019.