The Importance of Leaving Some Dead Trees

April 19, 2022

The oak woodlands and riparian corridors in the valley are full of a variety of trees and shrubs that provide food and shelter for many species of birds, mammals, insects, and other invertebrates. As these ecosystems grow and mature, the older trees begin to die off. Some fall over, literally coming right out of the ground and breaking off at the roots. Some split in half or thirds like some of our Valley Oaks have done, and others just die gradually, one large limb at a time. As we, as a community, begin to address the fire dangers in the forested areas we are living in by clearing and thinning woodlots, we should consider dead standing trees that are important habitat for birds and mammals. The need for fire protection is obvious, but it is painful to watch as large very old trees are taken down. Hopefully people are thinking about replanting and replacing some of the trees. Their importance to the ecological community is documented and quantified so their removal needs much consideration.

With this in mind, today I am documenting a Western Bluebird nest that we have in a nest box we put up last year at the Coleman House Office in the Willits Valley. During our staff meetings, we can watch the male and female bluebirds flying back and forth from the house across the pasture and into the riparian zone of Outlet Creek. When the female and male bird return, their bills are full of caterpillars or other insects to feed their young. The fledgling birds inside begin to chirp loudly as they enter the hole. Sometimes one will come out with a large white fecal sac. This is an important task that keeps the nest box clean and sanitary for the baby birds. They work nonstop, often one adult waits for the other as they are feeding in the box. What an opportunity to see this activity up close. Where are they finding all these caterpillars and bugs? It is a cool and grey day between the rains and all the worm-type insects they are bringing back are the color of leaves.

Western Bluebirds, Sialia Mexicana, are one of the many cavity nesting resident species of our county. Tree cavities are naturally formed hollows that are mainly found in older trees. Other cavity nesters include Oak Titmice, Chestnut-backed Chickadees, and Bewick’s Wrens. Woodpecker species that nest in cavities include Nuttall’s, Downy, Hairy, Pileated, Red-breasted sapsucker, and Northern Flicker. Wood Ducks, Mergansers, and Buffleheads also depend on tree cavities for nesting habitat. Even raptors like the American Kestrels nest in cavities. Then there are our cavity nesting owls such as the Northern Pygmy, Western Screech, Barn Owls and Northern Saw-whet Owl. The threatened Northern Spotted Owl also depends on dead tree snags and cavities for nesting. This wide array of birds needs cavities to nest in and most of the cavities are created by woodpeckers who are able to excavate them in dead snags or trees. This gives them a very important role in the lives of all those birds. We also have many nonresident birds that nest in cavities, migrants from Central and South America like Ash-throated flycatchers, Tree Swallows, Violet-winged Swallows, Rough-winged Swallows, White-throated Swifts, and Purple Martins. I have not named all our cavity nesting birds because there are 85 species in North America that depend on cavities to nest in.

This brings me back to the fact tree removal in certain cases is a necessary land management tool, especially the practice of taking out dead trees for fire safety. This is all understandable for us living in fire prone zones, but I want to put a word in for moderation and leaving a few dead trees and snags for bird habitat. One of the things that can work is to leave a nine- or ten- foot section of a dead tree for bird cavities. Just consider the benefit of this in terms of insect control and bird populations. Cavity nesting birds are running out of places to nest because there are fewer dead standing trees, so leaving a few trees with adequate hollows that also do not pose a hazard to habitable structures or powerlines is a win-win. In addition, installing bird nesting boxes with specific size openings for different species is helpful. Nonnative birds such as European Starlings and House Sparrows also use cavities and put more stress upon native cavity nesters that they compete with for available habitat.

As I watch the bluebird pair outside our office window, I am reminded that this man-made wooden box nailed to the power pole is the reason that this bluebird family is successful and that is takes an enormous amount of energy to produce a family of bluebirds. This is astounding and inspiring. Helping cavity nesting birds doesn’t only mean putting up bird boxes, it also means insuring we leave natural dead trees and snags for them to nest in.