Woodpeckers Main Thread in Nest Web

The lion may be the king of the jungle, but in the mature mixed forests of British Columbia's interior, woodpeckers rule the roost. A recent study by Environment Canada biologists shows that half the forest fauna in the region nest in tree holes, most of which have been excavated by these primary cavity nesters.

The study shows that two species of woodpecker and one species of tree are the main threads in a complex "nest web" that connects the diverse members of the cavity-nesting community. Of the eight woodpecker species found in the region, the Northern Flicker and the Red-Naped Sapsucker excavate 75 per cent of all cavities used by all species, and 90 per cent of those used by secondary cavity-nesting birds, which cannot create their own. Ninety-five per cent of the cavity nests found over the course of the study were in trembling aspen, a broad-leafed deciduous tree.

These findings confirm woodpeckers as critical to the composition and function of the entire forest ecosystem. Their nesting holes not only support 19 species of secondary cavity nesters—including ducks, songbirds and owls—but are also sometimes used by weak primary cavity nesters such as chickadees and nuthatches, which sometimes create their own holes, and by mammals such as bats and squirrels. Their feeding habits also provide other woodland species with access to food resources such as sap, beetles, ants and grubs. Woodpeckers are also important predators of bark beetles and other wood-boring insects that cause significant tree mortality.

The strong dependency of cavity-nesting species on woodpeckers makes it critical that the kind of habitat required by this keystone group be preserved. In addition to showing a strong need for trembling aspen for nesting, woodpeckers also spend 75 per cent of their foraging time in conifers. In both cases, they are highly dependent on old or dead trees with characteristic defects such as a broken top, sloughing bark, or the presence of decay, fungal infection or wood-boring insects.

While such trees are abundant in unmanaged mature forests, they are rare or absent in managed younger forests, where they are often removed as useless or dangerous to workers. Planted stands are less likely to contain the diversity of habitat features required by woodpeckers because they are often similar in age, size and species composition. In northern Europe, large-scale declines in woodpecker populations and other native wildlife have occurred where timber farms have replaced vast areas of once-natural boreal forest.

Environment Canada is involved in several studies in the B.C. interior to investigate habitat requirements and develop forest management guidelines for the conservation of these critical habitats. Recommendations to forest managers include leaving all dead trees standing where they pose no hazard to people or property, and retaining a mixture of mature healthy, diseased and dead deciduous and coniferous trees.

The Department is also continuing its work in the central interior of the province, where it is using experimental cut plots, in cooperation with forest companies, to test how nest-web structure shifts in response to different forest-cutting regimes. It is hoped that, through these tests, selective harvesting methods will be developed that will retain the full complement of native wildlife and ecological functions in B.C.'s forest ecosystems.

  Home |  Air |  Atmospheric Science |  Climate Change |  Environmental Action |  Habitat |  Pollution |  Species at Risk |  Technology |  Water |  Weather |  Wildlife