These include several passerine songbirds typical of shrub and forest habitats, such as thrushes, flycatchers, and warblers. Many of these species consume insects in the canopy of the boreal forest and other habitats. Populations of several boreal forest-breeding migratory thrushes, flycatchers, and warblers may be declining because of the loss of wintering habitat in the tropical forests of the world and the changes to or loss of forest habitats in the temperate zones along their migratory routes. The extensive lakes, ponds, and wetlands especially of the glaciated part of the boreal forest provide a large area of habitat for waterfowl and shorebirds, although the birds primarily occur in low densities across the landscape. Insects Almost all of the food webs that support fish in boreal forest streams are based on insects.
Some insect outbreaks can injure or kill trees across widespread areas of the boreal forest.
Once an outbreak reaches a certain size it can become self-sustaining, much like a forest fire. The spruce budworm and spruce beetle in North America are well known examples. Outbreaks can be triggered by unusual weather or physical injuries that stress trees and make them vulnerable. Outbreaks end for a variety of reasons in specific cases, including the stimulation of host plants to produce defensive chemicals, and competition for or depletion of susceptible host plants. These insects serve the ecological role of wood decomposition and nutrient release.