Conserve Ontario's Carolinian Forests: preserve songbird species at risk, chapter 5
Building Better Forest Habitat
These five forest songbirds prefer large forested landscapes for nesting. In Canada, the largest amount of forest cover within the Carolinian Zone is found in Halton and Norfolk counties, which are approximately 26% and 25% forested, respectively.
Examples of typical nesting habitat in Ontario
© Bill Rayner and Ron Kingswood
Acadian Flycatchers nest in steep-sided, wooded creek valleys, maple swamps, and moist maple-beech woodlands
© Bill Rayner and Ron Kingswood
Hooded Warblers nest in gaps within large, mature woodlands dominated by white oak, red maple, white pine and/or American beech
Large Habitat Required
These birds occasionally inhabit forests as small as 10 to 20 hectares (about 25 to 50 acres), but are much more common in forests of at least 100 hectares (about 250 acres). Cerulean Warblers are thought to prefer a minimum of 250 hectares (675 acres). Small forests can, and do, attract some of these species if they are in a landscape with larger amounts of forest cover within the region.
Building on Forest Interiors
Circular or square woodlands have proportionally more interior habitat than long, narrow woodlands of the same area. Strategic reforestation of edges and openings will increase the amount of forest interior habitat and result in larger forests.
Large mature forests with habitat more than 100 metres from the edges are more likely to contain the variety of specialized microhabitats these songbirds require for nesting, foraging and cover. They also represent a stage in forest development where occasional large mature trees in the canopy die and fall, thus creating natural forest gaps / openings and the specialized microhabitat preferred by Hooded Warblers.
Different from natural forest gaps / openings, hard edge habitat typically occurs in a fragmented landscape of smaller forests and is characterized by the boundary between two very dissimilar habitat types (e.g., forest and agricultural field). Hard edge habitat has a very different structure and function than interior forest habitat. For example, nest predators such as racoons may be more abundant in fragmented landscapes, where forest cover is present in small, more isolated forest patches, surrounded and divided by other land uses than in landscapes with large, intact forests. Fragmented forest habitat usually exists in settled landscapes and is characterized by forest patches mixed with fields, pastures, orchards and residential areas and a higher proportion of forest edge habitat.
Birds nesting in large continuous forest cover are exposed to fewer Brown-headed Cowbirds (Molothrus ater), a common forest-edge species. As “brood parasites,” cowbirds do not build their own nests. Instead, they lay their eggs in the nests of other bird species, which incubate the cowbird eggs and raise the cowbird hatchlings as their own. As a result, the host parents may raise few or none of their own young. The amount of edge habitat can be minimized by protecting large tracts of forest, and increasing the size of individual forests through re-forestation projects.
Benefits of Mature Forests
Mature forests, which are disappearing rapidly in southern Ontario, have special ecological significance. They often support a greater mix of tree and plant species, and habitats at different stages of succession, than younger forests. They also offer the diversity of habitats (microhabitats) required by a suite of area-sensitive forest birds, including species at risk. They have a much greater potential to contain, or be managed to retain and enhance, important old growth characteristics such as large trees, downed wood, cavity trees and multi-layered canopies.
Landowners who manage mature forests on a sustainable basis can maintain a continuous periodic income while maintaining woodland bird habitat with only slightly modifying return times and harvesting prescriptions. Also, by leaving some uncut areas and older seed trees of a variety of species, along with providing variable regeneration gap sizes, landowners will maintain overall forest stand diversity and health over the long term.
Public agencies that own or manage Canada’s remaining Carolinian forests are encouraged to manage these properties as mature forest stands. A strong commitment from public landowners will greatly enhance the survival of forest songbird species at risk and other Carolinian species with specialized habitat requirements, and will establish benchmarks for similar stewardship by private landowners.
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