Year of compilation: 2001
Also included in the site are Spencer Creek Gorge and Tiffany Falls. The flora and fauna of the valley and marsh have been well studied with an exceptional concentration of significant flora and fauna being present. Over 580 species of vascular plants have been recorded for the valley (17 nationally and/or provincially rare), and over 800 species for the marsh (25 of which are nationally rare).
During recent years, about 100 species of breeding birds have been recorded within the valley (one of the more species rich areas in southern Ontario). A relatively large proportion of these are neotropical migrants, of which the more abundant species are Red-eyed Vireo, Wood Thrush, Eastern Wood-Peewee, Ovenbird, and Scarlet Tanager. Of additional ornithological interest is the presence of both hybrids of Blue-winged and Golden-winged Warblers.
Dundas Marsh is an important area for migrating waterfowl, shorebirds, herons, raptors, gulls, terns, and songbirds. There is confirmed breeding evidence for three species at risk in Canada: Least Bittern (vulnerable), Cerulean Warbler (vulnerable) and Prothonotary Warbler (endangered), the latter having nested annually for the last five or so years, and has nested here regularly, but not annually, since at least the 1950s. In addition, Yellow-breasted Chat (vulnerable) possibly bred in 1974, as might a pair of King Rails (endangered) in the 1960s. Other breeding species include Double-crested Cormorant (121 nests in 1997), Blue-winged Teal, Common Moorhen, Yellow-billed Cuckoo, Whip-poor-will, Eastern Bluebird, Tufted Titmouse, Carolina Wren, Black-throated Green Warbler and Orchard Oriole.
Even with the recognition provided by these programs, the breeding bird community within the valley is under considerable and increasing pressure. The valley is located on the northwest edge of Dundas-Ancaster-Hamilton urban area, and as such is experiencing sustained pressure from development and other land uses. All of the nationally significant bird species present at this site, as well as many of the other neotropical migrants, are susceptible to development related pressures, especially increases in habitat- generalist nest predators such as squirrels, raccoons, opossums, skunks and cats. From a landscape perspective, the valley has more extensive forests and more forest interior than most areas in southwestern Ontario and is relatively well connected to surrounding natural areas by naturally-vegetated corridors.
The aquatic and wetland systems of Dundas Marsh have been adversely impacted by the cumulative effects of off-site manmade changes such as the moderation of fluctuations in the water level in Lake Ontario and increased sedimentation and poor water quality due to rapid urbanization of upstream areas. The extent and quality of the aquatic and wetland vegetation in this area has undergone a dramatic decline during this century, due to excessive sedimentation, excessive turbidity, the spread of non-native species, and feeding and spawning activities by carp (a fish-way has been built to help control the carp, however, and thus restore the native vegetation). Most of the area is public-owned as part of the Royal Botanical Gardens and is managed as a wildlife reserve and conservation education centre.
BirdLife International (2021) Important Bird Areas factsheet: Dundas Valley and Dundas Marsh. Downloaded from http://www.birdlife.org on 24/01/2021.