Snags are standing dead trees which provide food (insects), cover in bad weather and places to raise young.

Snags may be created from living trees if there is a shortage of safe natural snags. Created snags can be expected to last for a long period of time. Poor quality or deformed trees, such as those with broken tops or large branches, make excellent snags.

• Snags can be dangerous. Locate them well away from trails, roads, buildings, and other structures.
• Select conifers for snag creation as they normally last longer than deciduous trees. Snag trees should be at least 14″ in diameter.
• Top or girdle trees at or above the first whorl of branches, but at least 14 feet high (ideally, much higher). Smaller trees may be useful for some cavity nesters, as are stumps which are at least 3 feet high.
• A jagged top will decay faster and supply more habitat than a smooth-topped tree.
• Large branches extending at least 2 feet out from the trunk, can be cut to create foraging habitat on live trees not intended to be used as snags.
• Roosting slits and cavity starts may be added to created snags at the time of topping or girdling. However, do not put these features, or bird boxes, on existing snags.
• Roosting slits may be used by most bats and some birds, such as brown creepers. The slits should be at least 8″ deep and 2″ wide, and angled sharply upward into the cambium layer.
• Cavity starts allow decay causing fungus to enter the tree wound. These cavities may be used by flying squirrels, swallows, kestrels and smaller owls. They should be at least 6″ deep and 4″ high. In time, as rot progresses, these cavities may be used by a large variety of cavity nesters, such as pileated woodpeckers, nuthatches, chickadees and flying squirrels.

If you don’t have dead trees in your backyard, you can add one. Some backyard birders have taken dead trees and planted them in cement filled holes. The dead trees where placed in deep holes. I haven’t done this myself, but I have heard about it.

* Bird boxes of varying sizes will host many species, such as wood ducks and swallows. They can be erected in most forest stands depending on target species and stand characteristics. Bird boxes, however, do not replace the need for snags.

Information courtesy Washington State Department of Natural Resources.
http://www.dnr.wa.gov/htdocs/rp/stewardship/bfs/EASTERN/tipsforcreatingsnags.html

Watch this video of a Pileated Woodpecker at Longwood Gardens in Kennett Square, Pa. Snags are crucial to Pileated Woodpecker survival.