Wildlife trees: Animal magnets

Pileated woodpecker.
Pileated woodpecker. Photo: Glenn Thompson.

Many species of wildlife find shelter in trees, and not just in living trees. Trees are mostly cellulose, which is not living tissue, biologically speaking: hard for most organisms to digest but great for wildlife habitat. Once a tree dies, the habitat value of a tree and its wood seems to take off. Wildlife trees are standing dead (snags), defective live trees or down logs, all of which have large amounts of dead wood.

The three primary needs of wildlife are food, water, and shelter. Trees — living or dead — provide two of the three (food and shelter), while helping to maintain and filter local watersheds. Dead trees provide food by housing the insects that feed on the dead wood, and offer cover in the form of cavities, crevices or loose bark.

Woodpeckers’ special role

Woodpeckers will make new cavities in wildlife trees every year, or improve old ones, as a regular part of courtship and nesting behavior. These cavities in dead trees are prime real estate, used by many other species when the woodpeckers are done. Fledging rates (babies to adulthood) for cavity nesting birds are much higher than rates for those that nest on the ground. Non migratory species, such as the pileated woodpecker, will use cavities for roosting in the non-breeding season. Nuthatches and other small birds will sometimes communally roost in cavities together. Flying squirrels are known to cuddle through cold winter days (they are nocturnal) piled into cavities.

Up to 40 percent of Washington’s forest wildlife species — and not just birds — use dead wood for some portion of their life cycle. The list is long. A few of the species that use wildlife trees are:

  • Pileated woodpecker
  • Hairy woodpecker
  • Downy woodpecker
  • Red-naped sapsucker
  • Western bluebird
  • Douglas squirrel
  • Marten
  • Long-tailed weasel
  • Chipmunk
  • Flying squirrel
  • Bats
  • Western toad
  • Salamander
pileated woodpecker cavities in a larch snag
Multiple pileated woodpecker cavities in a larch snag in northeast Washington. After more than 35 years as a snag, the tree fell in 2015. Photo: Ken Bevis/DNR.

Wildlife trees, including standing dead trees, are so important to wildlife that Washington State’s Forest Practices rules require timber harvesters to leave behind several of these trees per acre.

Forest Practices Illustrated — a simplified guide to the state’s Forest Practices Rules — suggests that planning for timber harvests include retaining more wildlife trees than the minimums required  and creating additional snags from low quality trees (easily with mechanical harvesting techniques) when possible.

Today is National Bird Day. Check out opportunities to watch birds on DNR-managed state trust lands, and learn more about birds from the Washington Ornithological Society and American Birding Association.

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