IBA Dundas Valley and Dundas Marsh
Dundas, Ontario
Site Summary
ON005 Latitude
43.252° N
79.971° W
75 - 475 m
94.30 km²
coniferous forest (temperate), deciduous woods (temperate), mixed woods (temperate), scrub/shrub, rivers/streams, freshwater lake, freshwater marsh, mud or sand flats (freshwater), urban parks/gardens
Land Use:
Nature conservation and research, Fisheries/aquaculture, Not Utilized (Natural Area), Tourism/recreation, Urban/industrial/transport
Potential or ongoing Threats:
Agricultural pollution/pesticides, Disturbance, Filling in of wetlands, Ground water extraction, Intensified management, Interactions with native species/disease, Industrial pollution, Introduced species, Other decline in habitat quality, Other environmental events, Recreation/tourism, Urban/industrial development
IBA Criteria: Nationally Significant: Threatened Species, Congregatory Species
Conservation status: World Biosphere Reserve
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Site Description
The Dundas Valley is an extensive natural area located in southern Ontario along the Niagara Escarpment. Immediately to the east is the town of Dundas and Dundas Marsh (also called Cootes Paradise). The Spring Creek valley forms a narrow, natural corridor joining Dundas Valley to Dundas Marsh. Most of the Dundas Valley area is comprised of relatively undisturbed deciduous and mixed upland forest. The topography is quite varied, being comprised of rolling hills, deeply incised stream courses, and steep valley walls, with local relief of 30 metres or more being common. Dundas Marsh is located at the western end of Hamilton Harbour, and is a shallow flooded basin of open water and marsh joined to Hamilton Harbour by the Desjardins Canal. The shallow open water pond is dominated by water lilies and Sago Pondweed while the shoreline is dominated by cattail and Manna Grass. The surrounding terrain consists of rolling hills and ravines, covered woods and successional communities.

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).

The Dundas Valley contains a nationally significant community of forest birds. Breeding evidence for at least five nationally vulnerable, threatened or endangered species has been recorded. Two of these threatened species are regularly present in nationally significant numbers (i.e., greater than 1% of their national population). These species are the Hooded Warbler (two to four pairs annually), and Louisiana Waterthrush (two to four pairs annually). Cerulean Warbler (nationally vulnerable) is also present within the valley, but not in nationally significant numbers. Yellow-breasted Chat (nationally vulnerable) and Acadian Flycatcher (nationally endangered) have also been recorded within the valley, but only on an irregular basis.

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.

IBA Criteria
SpeciesT | A | I Links Date Season Number G C N
Acadian Flycatcher 1990 - 2018 SP 1
Acadian Flycatcher 1994 - 2018 SU 1
Barn Owl 2006 FA 1
Barn Owl 2006 SU 1
Barn Owl 2005 WI 1
Chimney Swift 1990 - 2020 FA 23 - 300
Chimney Swift 1997 - 2019 SP 25 - 100
Chimney Swift 2013 - 2016 SU 23 - 55
Common Goldeneye 1997 WI 10,456
Greater Scaup 1993 - 2010 WI 4,500 - 17,556
Herring Gull 1990 - 2008 WI 3,665 - 4,268
Little Gull 2006 FA 2
Little Gull 1990 - 2010 SP 2 - 4
Loggerhead Shrike 1997 - 2017 SP 1
Long-tailed Duck 1999 - 2011 WI 8,812 - 24,304
Louisiana Waterthrush 1995 - 2017 SU 4 - 6
Prothonotary Warbler 1991 - 2006 FA 1
Prothonotary Warbler 1994 - 2009 SP 1 - 2
Prothonotary Warbler 1990 - 2004 SU 1 - 8
Red-breasted Merganser 2009 - 2011 FA 9,965 - 10,540
Rusty Blackbird 1991 - 2011 FA 23 - 930
Tundra Swan 2013 SP 2,000
Yellow-breasted Chat 2000 - 2005 SP 1
Yellow-breasted Chat 1991 - 2006 SU 1 - 2
Note: species shown in bold indicate that the maximum number exceeds at least one of the IBA thresholds (sub-regional, regional or global). The site may still not qualify for that level of IBA if the maximum number reflects an exceptional or historical occurrence.
Conservation Issues
The significance of the Dundas Valley (and/or various portions of it) has been recognized through a variety of programs or designations. At the municipal level, it is identified as an Environmentally Sensitive Area in the Hamilton-Wentworth Regional Official Plan; at the provincial level, it is identified as both a Life Science and Earth Science Area of Natural and Scientific Interest, and also as part of the Niagara Escarpment Planning Area; and at the international level it is recognized as part of the Niagara Escarpment World Biosphere Site, and was examined under the International Biological Programme (IBP).

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.

The IBA Program is an international conservation initiative coordinated by BirdLife International. The Canadian co-partners for the IBA Program are Birds Canada and Nature Canada.
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