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The Dying Tree Nature’s Legacy: A Home for the Birds of Filoli

Categories: Blog

Our eyes dismiss a dying tree. We perceive it as useless and an eyesore. Our fears tell us to cut it down and haul it away quickly.

How often do we ask, “Does the tree need to be removed completely?” A tree has two lives. It’s second begins when it declines. Its commendable legacy is to benefit wildlife and ecosystems in ways it cannot when it is living. Imagine a time-share that is used by different species, for different purposes, in every stage of its demise.

Did you know about 80 birds in North America nest in tree cavities? Over time some cavities form naturally, often as a result of wounds. The larger ones may accommodate large owls, ducks, bear, fox, and other mammals. However, forest occupants, even those in some urban parks and gardens, have a good neighbor in the woodpecker—nature’s carpenter. This highly specialized bird excavates many nest and roost cavities in dead trees.

Photographed at Filoli by Danielle, iNaturalist.org

Filoli is home to several birds that are cavity nesters. One of these birds, the western bluebird, has suffered a serious decrease in their population since the 1970’s due to loss of habitat. In the early 1990’s, Filoli installed nesting boxes as part of the California Bluebird Recovery Program to provide nesting sites for successful breeding. Volunteers and staff collect information on species and number of eggs laid, hatchlings, and successful fledglings. This is reported to the California Bluebird Recovery Program and the Cornell Lab of Ornithology.

There are close to ninety bluebird boxes on the Filoli preserve which are monitored weekly through the nesting season (March to August). The boxes are also used by seven other cavity nesters such as violet-green swallow, tree swallow, oak titmouse, chestnut-backed chickadee, ash-throated flycatcher, Bewick’s wren, and the house wren.

There are also natural cavities and woodpecker-created cavities in Filoli’s plane trees. Acorn woodpeckers may reuse their previous nest holes, particularly if they have successfully fledged young from that site. Bewick’s wrens use the small natural cavities in the plane trees where the bark has separated from a rotting branch.

When these sites are vacated, they are inherited by about 40 other cavity-nesting birds that would otherwise be without homes in which to raise their families. Ah! But there’s more.

Stress cracks and spaces behind loose bark become pantries for nuts, berries, insects, and vegetation. These caches can tip the scale as to who makes it through a bitter winter. Such crannies provide shelter for small organisms as well. Look nose-close and you may discover bees, a roosting bat, or a lizard regulating its body temperature, escaping a predator or dining on insects breeding there. Insects in dead trees are a vital food source for wildlife. Unobstructed views overlooking the landscape are coveted by wildlife, so dead tree-tops and dead limbs serve as perches for hunting, territorial defense and courtship. To see and be seen!

When wisely applied, that’s one key to survival.

If a tree is allowed to die in place, over time natural elements, fungi and other decomposers ultimately convert the tree to duff and return its nutrients to the soil. But in the process, fungal fruiting bodies (think mushrooms) house insects which raise their families within their close, moist, fleshy corridors or under their leathery canopies. Furthermore, fungi become food for countless foragers, who in turn act as agents of forest succession by transporting fungal spores and mycelial fragments on their bodies. Through death, nature replenishes life.

There are overriding safety reasons to remove a dead tree, and not all locations are suitable for wildlife or acceptable to humans. However, if you ever want to consider retaining one, a licensed tree risk assessor should be consulted. But next time, when you see a red X on a dead tree, please ask, “Does it have to be removed completely?”

Gillian Martin is Director of the Cavity
Conservation Initiative.
To learn more about Cavity Conservation, click here cavityconservation.com