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Understanding how birds respond to disturbances in the forest

Scientists are studying birds in Canada’s boreal forest. Birds are abundant in the boreal because of its vast size and the variety of habitats that it provides.

Boreal chickadee. Photo: Kirk Zufelt
Boreal chickadee.
Photo: Kirk Zufelt

Birds are part of the enduring beauty of Canada’s forests. They are also a barometer of environmental change. How they respond to disturbances in the forest can suggest how other less visible or harder-to-study species are faring. Canadian Forest Service research aims to inform management decisions that account for bird habitat.

Population trends

The overall long-term population trends of most boreal bird species are either stable or increasing. But populations of some common bird species are in decline around the world, including some found in Canada’s boreal forest—for example, the rusty blackbird (Euphagus carolinus), Canada warbler (Wilsonia canadensis) and Connecticut warbler (Oporornis agilis).

Bird populations vary naturally, and the causes of population changes are complex and hard to attribute to any single factor. Population fluctuations may result from both natural causes (weather, fire, insect cycles) and human-related causes (climate change, fire suppression, forest management, forest loss, industrial activities).

The declines seen in some boreal bird species are likely related to various environmental changes and habitat loss and/or degradation that could be occurring on the breeding grounds, the wintering grounds or in migration stopover habitats. Research suggests that winter habitat degradation is one of the most significant factors affecting many migratory birds. Significant amounts of forest cover have been lost in some countries where birds that breed in Canada overwinter.

Impacts of forest harvesting

In Canada’s boreal forest, the impact of timber harvesting on bird populations is complicated, differing by species, region, forest type, harvest prescription, length of time after harvest, and so on. Forest harvesting may cause changes in bird species composition, diversity and abundance, and these changes can be positive, neutral or negative, depending on the species and the types of habitat that it uses.

For example, early successional species such as mourning warbler (Oporornis philadelphia), chestnut-sided warbler (Dendroica pensylvanica) and white-throated sparrow (Zonotrichia albicollis) benefit from harvesting, as they prefer a younger forest. But some forest-dependent species, such as brown creeper (Certhia Americana), boreal chickadee (Poecile hudsonica) and ovenbird (Seiurus aurocapilla) are sensitive to the loss of old forest habitat.

Other species, such as woodpeckers, require dead or dying trees for nesting and feeding, while others require the cavities created by woodpeckers in which to nest. Still others, such as raptors and flycatchers, use standing live or dead trees in clear cuts and burned areas, as perches from which to hunt. Protecting forests from fire can reduce the availability of these types of habitat features across the landscape.

Research has shown that harvesting patterns that emulate natural disturbances tend to benefit birds and other wildlife, and promote forest biodiversity in general. As a result, jurisdictions in Canada either require or are moving toward harvesting practices that aim to mimic natural disturbances, and are implementing ecosystem management practices to conserve wildlife habitat. Many provinces have also developed action plans to improve their knowledge of biodiversity in the forest by completing inventories, conducting research and carrying out environmental monitoring. In addition, industry is partnering with environmental non-governmental organizations to develop projects that advance boreal forest science and conservation.

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