Pileated woodpeckers are large woodpeckers native to forests in North America. They are known for their dramatic excavating activities on trees, which serve multiple purposes for the birds. Understanding what pileated woodpeckers do to trees provides insight into their unique roles in forest ecosystems.
Why Do Pileated Woodpeckers Excavate Trees?
Pileated woodpeckers excavate trees for several reasons:
- To create nest cavities – Pileated woodpeckers excavate large, rectangular holes in tree trunks to create their nest cavities. They prefer dead trees and trees with heart rot that makes excavation easier.
- To create roost cavities – Pileateds also excavate overnight roosting cavities, which are typically higher up in trees than nest cavities.
- To find food – Pileateds chip away at dead wood to reach carpenter ants and other wood-boring insects that make up a large part of their diet.
- To communicate – The excavation activities of pileateds serve as a form of communication, indicating territory boundaries and attracting mates.
By excavating cavities in trees, pileated woodpeckers provide nesting and roosting sites for themselves and many other animal species that cannot excavate their own cavities.
What Types of Trees Do Pileated Woodpeckers Excavate?
Pileated woodpeckers excavate a variety of tree species across their range, preferring trees that are dead, dying, or decayed:
- Conifers – Pileateds often excavate old, large conifers like hemlock, spruce, pine, and Douglas fir. The wood of these trees remains hard enough for cavity excavation even when dead or decaying.
- Aspen – Quaking aspen is a favorite tree of pileateds across the western United States and Canada.
- Cottonwood – Cottonwoods are a prime target for pileateds, as their wood stays hard for excavation after the tree dies.
- Oak – Oaks and other hardwoods are readily excavated in eastern pileated woodpecker habitats.
In general, pileateds prefer trees at least 15 inches in diameter at breast height for excavation. They gravitate toward trees infected with fungus, like heart rot, that softens the interior wood and makes excavation easier.
What Does a Pileated Woodpecker Excavation Look Like?
The excavations of pileated woodpeckers are unmistakable. Key identifying features include:
- Large, rectangular holes – Pileated excavations are large, rectangular holes up to 6 inches tall and 4 inches wide. Nest entrance holes are more horizontal while roosting holes are more vertical.
- Chiseled edges – The edges of pileated woodpecker holes have a chiseled, sometimes scalloped look from the bird’s chisel-like bill.
- Deep cavities – Cavities are often excavated very deeply into a tree, up to 26 inches deep for nests and 18 inches for roosts.
- Plastering – Pileateds coat the interior walls of their cavities with a layer of fresh wood chips, or “plaster,” probably to help control humidity and temperature.
Distinct rectangular holes with chiseled edges are a hallmark of pileated woodpecker excavation on dead or dying mature trees. The size and depth of the holes set them apart from other woodpecker species.
Pileated Woodpecker Excavation vs. Sapsucker Holes
Pileated woodpecker holes are sometimes confused with the equally distinctive rows of small holes created by yellow-bellied sapsuckers. However, sapsucker holes penetrate live trees to feed on sap, while pileateds excavate into dead wood.
What Tools Do Pileated Woodpeckers Use?
Pileated woodpeckers have several specialized tools and adaptations that allow them to excavate cavities in hard wood:
- Chisel-like bill – The long, chisel-shaped bill of the pileated can deliver 500-700 blows per minute to pound out cavities.
- Hyoid bone – This flexible bone under the tongue wraps around the skull to act as a shock absorber, protecting the woodpecker’s brain.
- Zygodactyl feet – With two toes pointing forward and two back, these feet grip vertical surfaces tightly.
- Tail feathers – The stiff tail feathers of pileateds brace them upright against gravity on vertical trees.
Using a combination of specialized tools and anatomy, pileateds can hammer, carve, and chip away at wood to construct their characteristic rectangular cavities.
How Does Pileated Woodpecker Excavation Impact Trees?
The extensive excavation of pileated woodpeckers can have significant impacts on trees. Negative effects include:
- Structural weakening – Deep holes and cavities reduce the structural integrity of trees, making them more prone to cracking or blowing over.
- Stress and disease – Open holes allow in water and fungi that decay the heartwood of living trees.
- Tree death – Girdling, or removing the band of living phloem tissue under the bark, can sometimes kill trees.
However, pileated excavation also benefits trees and forests by:
- Increasing wildlife habitat – Cavities provide homes to numerous bird and mammal species.
- Speeding nutrient cycling – Decaying wood releases nutrients back into the ecosystem faster.
- Thinning forests – The resulting tree deaths thin overly dense forests.
The extensive excavating behavior of pileated woodpeckers makes them a keystone species that shapes forest structure and dynamics.
Unique Benefits of Pileated Woodpeckers for Forests
As one of the primary cavity excavators in North American forests, pileated woodpeckers confer several ecological benefits to birds and other wildlife:
1. Nesting Cavities for Other Species
Many species rely on the nesting cavities created by pileated woodpeckers, including:
- Wood ducks
- Hooded mergansers
- Barrow’s goldeneyes
- American kestrels
- Northern flickers
- Eastern bluebirds
- Tree swallows
- Bats
Saw-whet owls, pine martens, and squirrels may also use old nest holes. Cavities carved out by pileated woodpeckers are especially crucial for large cavity nesters like wood ducks and hooded mergansers.
2. Roosting Cavities for Winter Warmth
Many birds and mammals also take shelter in the roosting cavities carved by pileateds, including:
- Chickadees
- Woodpeckers
- Nuthatches
- Bluebirds
- Titmouse
- Squirrels
- Bats
- Pine martens
These existing cavities provide crucial winter refuge from harsh weather and predators.
3. Feeding Opportunities from Dead Trees
As pileated excavations often lead to tree death, the resulting dead and dying trees provide an abundance of food sources:
- Insects like beetle larvae in the decaying wood
- Fungi and lichens growing on the bark
- Sap from gaps in the bark
Birds like woodpeckers, nuthatches, and chickadees forage extensively on dead trees. Dead trees also attract insects that are food for flycatchers and bats.
4. Increased Structural Diversity
The snags and fallen logs resulting from pileated woodpecker activity add structural diversity to the forest floor habitat, benefiting species like:
- Salamanders
- Frogs
- Snakes
- Small mammals
Openings in the forest canopy allow sunlight to reach the forest floor, increasing understory plant growth.
Key Facts About Pileated Woodpecker Excavation
To summarize key points about pileated woodpecker excavation:
- Purpose: Pileateds excavate trees primarily for nesting and roosting cavities.
- Tree preferences: Dead or decaying large trees like conifers, aspen, cottonwood, and oak.
- Identifying traits: Large, rectangular holes with chiseled edges, often deeply excavated into heartwood.
- Tools: Specialized anatomy like chisel-shaped bill, flexible hyoid bone, zygodactyl feet, and stiff tail.
- Impacts: Can weaken, stress, or kill trees but also provide wildlife habitat.
- Benefits: Cavities for other wildlife, winter shelter, feeding opportunities, increased diversity.
Understanding details of the pileated woodpecker’s excavating behavior provides insights into their keystone ecological roles in forests across North America.
Conclusion
Pileated woodpeckers are adept at excavating rectangular cavities in living and dead trees for their nests and roosts. Their specialized tools and anatomy allow them to chisel out extensive holes in even hard wood. While this excavation can damage or kill trees, it also confers major ecological benefits. The nesting and shelter cavities provide homes for numerous species of birds, mammals, and other wildlife. Dead trees resulting from pileated activity supply food sources and increase structural diversity. By physically altering forest structure and dynamics, the pileated woodpecker fills an important keystone role across the forests of North America.