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“It is now clear that to maintain a rich bird fauna, conservationists in eastern North America should focus on preserving large tracts of forest of several hundred acres or more – rather than many small tracts. And contrary to traditional wildlife management, which often seeks to create edge habitat, protected woodlands should be spared intrusion by roads, power lines and clearcuts.”
Raymond J. O’Connor, Professor of Wildlife at the University of Maine in Orono and coauthor of Farming and Birds.
Concern over songbird decline has grown over the past decade, as research scientists and amateur birders alike report a severe drop in the number of tropical migrants nesting in forests. While we have little data from Prince Edward Island, it is reasonable to assume that chopping forests into small pieces and creating large amounts of edge has caused the same problems here. Yet there has been an ominous silence about this potentially devastating development.
Edges are those areas where one type of ecosystem meets another, such as forest to field or forest to clearcut. The benefits of edges form the rationale for much forest management. Studies show that numbers and species of wildlife increase, notably game such as ruffed grouse and snowshoe hare. Clearcutting patches in continuous forest creates a lot of edge, benefiting a very specific type of wildlife, usually already common, at the expense of other, rarer species. Forest fragmentation, where we create a great deal of edge and deplete the amount of continuous forest, is taking place at an increasing rate in this province. Large tracts of forest are constantly being carved up by roads, clearcuts or developments.
In an effort to improve the health of our forests and create a model for environmental stewardship, Macphail Woods is launching the Restore an Acre initiative.
You can mail a cheque (payable to Macphail Woods) to Gary Schneider, Box 11, Belfast, PEI C0A 1A0, or donate online through CanadaHelps.
In this fragmented habitat, certain predators or parasitical bird species thrive at the expense of other bird species. Blue jays, common grackles, crows, raccoons, skunks and even domestic cats and dogs are much more common alongs edges and can prey on eggs and nestlings. Species most at risk are the migrant songbirds. Some, like the ovenbird and black-and-white warbler, nest on the ground where predation is especially high. Others build cup-shaped nests, more vulnerable than dome-shaped nests or tree cavities used by many year round residents. Migrants also face the disadvantage of arriving late and leaving early. If they lose one clutch of eggs, there is not time to lay and raise another. They are also usually too small to fight off predators.
Parasitic brown-headed cowbirds, which lay eggs in nests of other birds, are also prospering. A female cowbird may lay up to 40 eggs per season, one or two eggs per nest. A cowbird will replace one of the eggs in a red-eyed vireo nest, for example, with her own. The parent vireo devotes so much energy to feeding the fast growing cowbird young that its own offspring often do not survive. The open nests of migrant warblers, thrushes, vireos and flycatchers are easy targets for cowbirds.
A Wisconsin study showed nests at the edge of a forest to be five times as likely to contain cowbird eggs as those nests more than 275 m (300 yards) from the edge. In a large area of parkland in Maryland that continues to be fragmented, there were 198 pairs of breeding pairs of migrant songbirds for every 40 hectares (100 acres) of parkland in 1948. By 1986 there were only 31 breeding pairs of migrants every 40 hectares (100 acres). Other studies have shown that birds such as the barred owl, red-eyed vireo, scarlet tanager and ovenbird require large areas of unbroken forest.
Another associated problem with forest fragmentation is that the birds most effected are insect eaters – we simply do not know if the absence of these songbirds will lead to greater insect infestations in the future.
Prince Edward Island already has a lot of edges – roads, riparian zones, hedgerows dividing farm fields, even gardens and orchards. What we lack is continuous forest. To make matters worse, this is not just an isolated instance – it is happening across North America.
Roadways and clearcuts create edge in woodlots – not always a good thing.
What you can do: