Pileated woodpeckers are large woodpeckers native to forests across North America. With their loud, distinctive calls and large excavated nesting and roosting cavities, these birds are a sign of mature forests. However, some people have concerns that pileated woodpeckers may damage or even kill trees when they drill into them to create nesting or roosting cavities. In this article, we’ll explore the potential impacts pileated woodpeckers can have on trees and forests.
Do pileated woodpeckers drill holes in live trees?
Yes, pileated woodpeckers do drill into live trees to create nesting and roosting cavities. They use their strong, chisel-like bills to excavate large, rectangular holes in tree trunks and branches. Pileated woodpeckers prefer dead trees for nesting and roosting, but they will also excavate cavities in living trees, both healthy and diseased.
Cavities are often excavated in soft wood like aspen, cottonwood, willow and alder. However, pileated woodpeckers will also excavate into harder woods like oak, maple, hickory, birch and pine. Certain tree diseases that cause decay, like heart rot fungus, can make the wood easier to excavate.
What is the size of cavities excavated by pileated woodpeckers?
Pileated woodpecker nesting and roosting cavities are quite large compared to other woodpecker species. The entrance hole is typically oblong or oval in shape and ranges from 3-6 inches tall and 2-5 inches wide. However, larger entrance holes up to 10 inches tall have been documented.
The depth of the cavity can range from 15-35 inches. Pileated woodpeckers excavate deep into the tree to create a nest chamber large enough to accommodate their bodies. The interior cavity is wider than the entrance hole, creating space to roost, nest and raise young.
Do pileated woodpeckers weaken or kill trees when they drill cavities?
Drilling into live trees does not necessarily mean pileated woodpeckers are killing or significantly weakening them. Healthy trees have defense mechanisms that help compartmentalize wounds and prevent decay from spreading. Here are some factors to consider:
Tree species and health
Some tree species, like aspen and birch, are more vulnerable to damage because they have thinner bark and wood. But even in these species, only extensively excavated trees are at serious risk. Diseased or declining trees are more susceptible to damage as well. Healthy, vigorous trees are better able to wall off wounds.
Size and depth of cavity
Larger, deeper cavities that remove more inner wood put more stress on a tree. But pileateds generally do not excavate beyond what is needed for the nest. Shorter, more shallow cavities reduce risk.
Location on tree
Cavities excavated higher on the trunk or in branches are less likely to impact structural stability than cavities low on the main trunk. The canopy supports limbs where cavities are often dug.
Age of tree
Younger, faster growing trees can heal over small wounds more quickly than older, slower growing trees. Mature trees tend to better compartmentalize wounds.
What are the potential impacts to trees?
While healthy trees can typically tolerate excavation, there are some potential impacts:
– Structural weakening – Extensive excavation of the main trunk can make trees more prone to breaking from winds or storms.
– Decay organisms entering – Fungi and bacteria can infect the exposed inner wood, leading to decay. Compartmentalization minimizes this.
– Animal entry – Squirrels, raccoons, and other wildlife may enter the cavity, enlarging it and increasing decay.
– Water entry – Open cavities provide an entry point for rain and moisture. This can lead to rot over time. Pileateds often excavate on the underside of leaning limbs to prevent this.
– Reduced growth rates – Less photosynthetic area from foliage loss above cavities can slow growth.
However, research suggests these impacts are generally minimal to moderate for most excavated trees. Severe structural damage or mortality is uncommon.
Do pileated woodpeckers prefer dead or living trees for cavities?
Pileated woodpeckers strongly prefer dead and dying trees for excavating cavities when available:
– In one study of pileated nest trees in Oregon, 92% were in dead trees and only 8% were live trees.
– Across North America, 78% of pileated nest trees are dead. Just 22% are live trees.
– They prefer dead trees with heart rot fungus, which softens the interior wood and makes excavation easier.
Live, healthy trees are not preferred. But pileateds are opportunistic and will use them for cavities in areas where dead and diseased trees are limited. Forest management practices that retain dead snags and diseased trees can provide abundant nesting habitat and reduce excavation of live trees.
Percentage of pileated woodpecker nest trees that are dead vs. live
Tree condition | Percentage |
---|---|
Dead | 78% |
Live | 22% |
Do pileated woodpeckers excavate a new cavity each year?
Pileated woodpeckers may excavate a new cavity every nesting season, but frequently reuse old cavities:
– One study in Oregon found pileateds reused old cavities 49% of the time.
– In Missouri, 40% of cavities were reused.
– Across North America, reuse rates vary from 25%-60%.
Reusing old cavities reduces the number excavated in live trees each year. And even when not used for nesting, old cavities provide valuable year-round roosting sites.
So while new cavities are excavated annually, pileateds do not abandon old ones. These remain available for future nesting and roosting.
Pileated woodpecker cavity reuse rates
Location | Reuse rate |
---|---|
Oregon | 49% |
Missouri | 40% |
North America | 25%-60% |
How many cavities do pileated woodpeckers excavate per year on average?
Pileated woodpeckers may excavate multiple cavities within their breeding territory each year. However, not all of these are used for nesting. Here are some estimates:
– One cavity per breeding pair is used for nesting.
– An additional 1-3 (or more) incomplete cavities may be excavated for roosting sites.
– Pairs excavate on average 2-4 cavities total per year.
– Older cavities from previous years remain usable for nesting or roosting.
So while the total number excavated annually is small, pileateds maintain a number of usable cavities within their territory. This network provides important nesting and roosting options over many years.
Do pileated woodpeckers damage trees when foraging?
In additional to excavating nest and roost cavities, pileated woodpeckers may damage trees when foraging:
– They sometimes peel bark from trees to access carpenter ants and other insects underneath. This can create large, elongated trenches in the bark.
– They may chip away at wood to dig out carpenter ants. This can leave shallow pits scattered across trunks and limbs.
– On dead trees, they excavate extensively when searching for carpenter ants, sometimes covering the entire surface with shallow excavations. This does not impact the health of already dead trees.
– Pileateds rarely drill into live wood solely for foraging. Their excavations are usually associated with roosting or nesting behavior.
So some bark removal and superficial wood excavation does occur when foraging. But this is generally minor and not a serious threat to tree health. It does not compare to the larger cavities dug out for nesting and roosting sites.
What tree species are preferred by pileated woodpeckers?
Pileated woodpeckers occupy a diversity of forest types across North America. They will excavate cavities in many species, but some are preferred:
Live trees
– Aspen
– Birch
– Cottonwood
– Willow
– Maple
Dead trees
– Aspen
– Birch
– Pine
– Fir
– Oak
Tree condition is more important than species. They strongly prefer dead or diseased trees with heart rot fungus when available. Live, healthy trees are excavated when dead/diseased trees are limited.
Forests with a mix of tree species and ages, and an abundance of standing dead trees, provide ideal habitat for pileated woodpeckers.
Do pileated woodpeckers prefer forests with dead trees?
Yes, pileated woodpeckers strongly prefer forests with abundant dead and dying trees:
– Dead trees provide easier excavation and more stable cavities than live trees.
– Heart rot fungus in dead trees helps soften interiors for excavating.
– Dense mature and old-growth forests have more dead trees available.
– Dead limbs on live trees are frequently used for cavities.
– Dead trees are preferred for foraging on carpenter ants.
– Forests lacking dead trees, like some intensively managed plantations, offer poor habitat.
Maintaining dead trees across the landscape provides vital nesting and foraging resources for pileated woodpeckers.
Do pileated woodpeckers prefer younger or older forests?
Pileated woodpeckers strongly prefer mature and old-growth forests:
– These forests contain larger diameter trees required for cavity excavation.
– More dead and dying trees are present for nesting/roosting.
– Mature forests support higher populations of carpenter ants.
– Pileateds are rare in young forests and small woodlots due to lack of resources.
One study across the U.S. found:
– 75% of pileateds occurred in old-growth forest.
– 24% in mature second-growth forest.
– Just 1% in young second-growth stands.
Restoring and maintaining older forest characteristics provides some of the most valuable habitat for pileated woodpeckers across their range. Their populations decline in younger, intensively managed forests.
Pileated woodpecker use of different aged forest stands
Forest age | Pileated occupancy |
---|---|
Old-growth | 75% |
Mature second-growth | 24% |
Young second-growth | 1% |
Conclusion
Pileated woodpeckers play an important ecological role in forests as primary cavity excavators. While they do excavate cavities in live trees, severe impacts to tree health and mortality are relatively uncommon:
– Healthy vigorous trees can typically tolerate excavation, compartmentalizing wounds.
– Pileateds preferentially use dead and diseased trees when available.
– Old cavities are frequently reused rather than new ones excavated each year.
– Impacts from foraging behavior are generally superficial.
– Certain tree species and forest types are preferred.
Management that maintains forests with diverse ages and tree species, abundant dead and dying trees, and mature to old-growth characteristics will provide excellent pileated woodpecker habitat and minimize excavations in live trees. Overall, the benefits pileateds bring to forest ecosystems through cavity excavation and insect predation outweigh their limited impacts on individual trees. Their presence is an indicator of woodland health.