The Plight of the Ontario Pileated Woodpecker
Between the mid-1700s and the early 1900s most of southern Ontario’s old-growth forests were destroyed by logging, forest fires, and settlement. The European market took the best pines and oaks and many of the remaining forests burned in accidental fires that swept through after the cuts. The forest was also burned to clear the land for farming.
This caused numbers of the Pileated woodpecker, who prefer large undisturbed tracts of forest, to decline sharply.
Steps were taken to stop this decline. There are management guidelines in order to preserve trees in Ontario for woodpecker habitat. They have rebounded to a certain extent.
The guidelines include that a minimum of 6 cavity trees (trees that have pre-existing cavities for nesting or that could have cavities made in them for nesting) must be preserved per hectare (1 square/km) when logging. Thinking ahead they also make sure that they retain trees to meet the needs of pileated woodpeckers and other cavity users for the next 20 years. Priority is given to:
retain pileated woodpecker roost trees, pileated woodpecker nest trees, trees with other woodpecker nest cavities or natural nest or den cavities, trees with escape cavities, trees with feeding excavations, and potential cavity trees.
Because pileated woodpecker roost trees are rare, these trees were to be retained even if dead while maintaining certain precautions for health and safety. Standard management procedure.
Unfortunately,
If a forest worker believes a cavity tree poses a safety risk, it must be felled or operations in the vicinity must be avoided.
Considering that most companies are interested in profits, avoiding certain sections of the forest just to leave a standing tree for birds may or may not happen. When you drive by a recently razed area how many standing trees can you count?
"Before it has completely decayed, a dead tree will play a role in that ecosystem for probably three or four times longer than it did when it was alive," explained Ellen Macdonald, a U of A forest ecologist who was part of the international team that conducted the study.
In production forests, harvesting and thinning interfere with natural [dead wood] dynamics, that is, the initial pulse of [dead wood] enrichment caused by a natural stand‐replacing disturbance and the subsequent slow accumulation of [dead wood] due to self‐thinning, minor disturbances and natural mortality as trees age. Thus, timber harvesting influences the amount and composition of [dead wood] for many decades. Even forest reserves can have low levels of coarse [dead wood] if they were managed for timber production before being protected.
The current scarcity and slow accumulation of [dead wood] in many forest ecosystems suggests that interventions aiming at rapidly in-creasing the amount of [dead wood] might be needed to support biodiversity.
Strangely too, the most detailed work on the habitat needs of pileated woodpeckers, which occurred in Oregon, recommends retention of 8 standing dead trees/ha for feeding, nesting and roosting. Why use the study that uses less trees and only has guidelines for 6 per hectare?
It’s an acquired taste
Remember when we were learning about caterpillars being mandibulate (chewing) insects - they get a taste for a certain food, and it becomes their all time favourite, and just like your little sister, that’s all they will eat.
Woodpeckers eat bugs, and many bugs are like that. As research is done into bug types found in trees certain correlations were found. The abundance of a particular tree in a specific region over extremely long periods of time meant that it usually had more bugs eating it. You know the phrase “it’s an acquired taste”? The same goes for bugs and the plants they eat. If something is new, like Scotch, and they have a relatively young palate, they won’t appreciate it and won’t eat it. But if it’s something they’ve had over and over again for generations, like mac and cheese, they gobble it down.
T. R. E. Southwood wrote an interesting article for the Journal of Animal Ecology (Vol. 30, No. 1, May, 1961) - The Number of Species of Insect Associated with Various Trees - detailing the connections to indigenous trees of Britain and the amount of wildlife that they support as well as the lack of wildlife to be supported by recent introductions. And by introduced I don’t mean new last year, or last century, I mean introduced c. 1200. Studying trees in Britain, Russia, Cyprus, and Sweden he found that the number of bugs changed based on whether the tree had a long, abundant history in that country or not. Even suggesting that certain, apparent, introduced species that supported higher counts of bug species were actually not really introduced, they had been present before the last glacial phase and were merely extirpated until brought back.
This helps us to see that what 6 trees are left standing have a huge impact on the amount of bug life that they support and because of that, the amount of woodpeckers they can feed.
Is that number really reasonable for Pileated populations to thrive?
Without knowing the species of trees left standing that’s a little tricky. But let’s look at some numbers:
Pileated woodpecker population density was estimated to be about 2 to 10 breeding pairs per 1000 hectares (10 km2) in both northern and southern Ontario when the management guidelines report was written in 1996. 1000 hectares will possess 6000 trees as long as no one thought there was a safety risk.
The same report states that territory (or home range) size can be anywhere from 40 to 260 ha in eastern North America. The pair stays together on its territory all year round, defending it in all seasons, but will tolerate new arrivals during the winter.
Let’s go with the middle number of 6 pairs per 1000 hectares. That means 1000 trees for each pair or 500 trees per bird. On paper that seems pretty generous.
The oldest known Pileated was a male that was almost 13 years old when he was recaptured in Maryland. Let’s say that’s atypical and they only reach 10 years old.
In Ontario forests 157 alien plant species have been found across all forested ecoregions. Of these alien plant species, 121 are considered invasive, some of the most common being: broad-leaved helleborine, European buckthorn, bittersweet nightshade and garlic mustard. Because some of these are trees and they are not native bug populations will be negligible as per Southwood’s article. These non-natives will impact the forest with time but we’ll only focus on right now.
Let’s be conservative and only knock off 50 non-natives for negligible bug populations. Down to 450 trees per bird or less.
Pileated woodpeckers excavate a cavity each year for nesting. Nest cavities are excavated in the decayed heartwood of standing trees. The cavity is generally about 20 cm in diameter or slightly smaller than your average dinner plate and up to 75 cm deep (twice the length of my fingertips to my elbow). The nest is accessed by an entrance hole that is about 10 cm in diameter.
Most nests are in hardwood trees, 15-70 feet off the ground, with poplars (Populus spp.) the tree of choice. Tree size is important. Nests have been located in trees as small as 25 cm dbh (diameter at breast height) but are generally found in trees 40+ cm dbh. A tree that is 40 cm in diameter, at breast height, would be approximately 25m tall. Again how many of these trees have you seen around?
There’s 10 trees that need to be a specific size to nest in and then are not reused - 440 trees left per bird, or less.
As a side note: because the Pileated Woodpecker prefers large trees for nesting in young forests, it will use any large trees remaining from before the forest was cut (those 6 left behind). Unfortunately, these trees are larger than the rest of the forest, so they present a lightning hazard to the nesting birds.
Moving on to food choices, they absolutely love carpenter ants! They will listen for ant activity in an old rotting tree and then peck through the wood, using their long, very sticky tongue to get the ants. Pileateds also feed on ground ants, beetles, cluster flies, moths, mosquitoes, caterpillars and other larvae as well as a small amount of fruits and nuts such as wild grapes, dogwood berries, cherries, and acorns.
How many carpenter ants live in a dead tree?
That is the question.
A carpenter ant nest is rarely bigger than a couple square feet and each nest is a highly organized colony, with a queen and hundreds or thousands of workers. Would we say that there is one per tree? They prefer damp or rotting wood nests because they feed on fungal growth and the softer fibers make tunneling easier. Workers may travel hundreds of feet from their nest in their search for food using foliage or branches to move through the forest.
If all of those 440 trees had the perfect damp, rotting wood conditions well suited to a carpenter ant nest, and if each nest had 5000 workers, that would equal 2,200,000 ants per 1000 hectares.
In one observation a parent bird was seen visiting their nest 210 times per day (each time carrying five insects on average). That means that one parent gathered 1,050 insects per day. Combined with the second parent, more than 2,000 insects per day were brought to their babies. That is more than 14,000 insects per week or 420,000 insects per month just by one pair of woodpeckers. That didn’t include what they were eating, only what they were bringing to the nest.
On average there are 4 young per nest that stay until the fall. They hatch as early as the middle of May but more typically in early June.
So 6 birds, 880 trees, 4,400,000 ants and they eat 105,000 ants a month, per bird, give or take.
If all of the babies survive (unlikely) and they stay with the parents for 5 months that’s 3,150,000 ants necessary to feed everybody.
We appear to have a 1,125,000 ant surplus on our hands.
Is this enough?
Considering as carpenter ants are one out of the thousands of bugs that live in the forest and the pileated woodpeckers will eat other things it appears to be an alright number.
But then we remember that pileated woodpeckers are also only one of the hundreds of birds found in the forest, and birds aren’t the only animal that eats bugs as we’ve already learned in our food webs post from last week.
There are more than 50 forest-dwelling species that depend on holes created by pileated woodpeckers for homes. Wrens and nuthatches will follow them around gleaning on their finds. This includes mergansers, wood ducks, flying squirrels, owls, bluebirds, and martens.The same study about the pileated states: Yellow-bellied Sapsuckers (Sphrapicus varius), Hairy woodpeckers (Picoides villosus), and Northern Flickers (Colaptes auratus) are thought to have breeding densities of 11 to 100 pairs per 10 km2 in the same area.
Everybody has babies, and everybody is hungry.
More than nesting trees and food
In order to conserve energy and stay warm, especially during winter, Pileated woodpeckers use cavities in special roost trees. These roosts also help them to avoid predation.
Sometimes they will use an abandoned nest cavity as a roost site, but they prefer a specific type of tree. These are large hollow trees (40+ cm dbh), different from the solid but decayed trees used for nesting, with multiple entrances, sometimes up to 10. Entrances are either natural, made by seams or broken tops off the tree, or excavated by the woodpeckers (similar in size and shape to entrance holes to nest cavities).
Even though it has been shown that the Pileated can adapt to a wide range of forest types for feeding, nesting and roosting, studies suggest a strong preference for mature, dense forests - large uninterrupted patches of woodland, covering territories of 100 to 200 acres, not just 6 trees here and there. Old growth stages of aspen (Populus tremuloides), aspen-balsam poplar (Populus balsamifera), red maple (Acer rubrum), and sugar maple-yellow birch (Betula lutea) are preferred.
These dead and declining trees, and downed woody debris in the forest, are critical components of pileated woodpecker habitat. A number of studies have suggested a direct relationship between the size of pileated woodpecker home ranges or their density and the supply of these habitat components.
In Oregon, Bull and Holthausen (1993) suggest that a typical 364 ha home range should have
all forest cover in mature or old growth stages with at least 25% in old growth,
at least 50% of the forest cover composed of stands with 60%+ canopy closure; and
at least 40% of the forest cover in an uncut condition.
In Manitoba, Millar (1994) suggests that a typical 250 ha home range should have
at least 40% of the habitat suitable for nesting,
the remaining habitat suitable for foraging, and
no more than 10% of the area in clearcuts.
A number of researchers have further suggested that the pileated woodpecker may be an area-sensitive or forest-interior species, i.e., one that requires relatively large contiguous blocks of suitable habitat. If true, the size and connectedness of patches of suitable habitat within home range-sized areas may be as important as the total amount of suitable habitat available.
This takes us back to the Westcountry Hedgelayer. If there are not contiguous blocks of habitat certain species just die out. These old school corridors used to provide at least a margin on the edges of agriculture in order for species to continue. But as these margins got increasingly smaller and then were wiped out entirely species disappeared. The Greater Prairie Chicken, the Karner Blue Butterfly, both of these species had their habitat completely taken away and so they left Ontario for good.
This has been acknowledged when it comes to our forests - clearcutting generally creates habitat that is unsuitable for feeding, nesting or roosting. These necessary trees are gone, the security cover is gone, machines and residual herbicides do untold damage and then, by the time the trees start to get big enough (Development Stage) they get cut down again.
What does Development Stage mean?
The Forest Resources Ontario 2016 report states:
“The term development stage refers to the current stage growth and development of a forest stand. This classification provides a way of tracking the silvicultural progress of a forest stand, starting with a recently depleted (by harvest or natural processes) through a young initiated stand and finally a successfully renewed stand.”
This is what is considered to be properly managed forest.
In response to recent wildfires in California they are taking a completely different approach.
The article Tree-planting programs can do more harm than good by Saul Elbein explains:
An important, often-forgotten characteristic of forests: left to their own devices, they expand. In a recent study, Brazilian ecologists charged with reforesting a cleared forest planted with virulent African cattle grass compared what happened when they cleared the grass and planted trees—versus just clearing the grass.
To their delight, they found tree-planting was unnecessary: five years after harrowing the grass, the test plots were full of native trees. Future foresters, they wrote in Forest Ecology and Management, should try “first evaluating the potential for natural regeneration and then gradually eliminating barriers."
Without fire, this entire area actually wants to be forest. Maybe micromanaging will give way to trees being allowed to just exist as they wish to in their native habitat. Prairies only occur with fire wiping out the non-prairie plants that slowly creep along the verge trying to gain a foothold.
Considering that there hasn’t been a wildfire here in, well, as long as people have been here from what I can find, I don’t think Tallgrass Prairie will naturally develop. Disturbed sites would naturally turn into meadow, then shrubs and small trees would gain a foothold allowing for the slow and steady march of a full fledged forest.
Why not use the natural approach?
That article offers an interesting scenario:
When they go out to begin replanting in the wreckage of the King Fire, North said, they will try a different variety of local initiative: a strategy called Individual-Cluster-Open, or ICO: a mixture of individual trees (which can grow big), clusters of trees (which support each other through their mycorrhizal networks), and open spaces that can fill with shrubs or new species and serve as firebreaks.
They also advocate that USDA foresters mix in a variety of species, rather than just the quickest growing pines, catering the species they plant to local microclimates: an approach more like a vast, variegated garden than traditional monolithic silviculture.
And in response to the funding squeeze, they’ll do something even more extraordinary: when they go back into the “green donut,” the USDA will likely leave most of it unplanted. They will leave the inner edges of the burned lands alone to slowly fill in with natural seedlings; picking only the most promising microclimates to try the ICO method.
And on the steepest terrain, they will use a method, borrowed from Latin America, that North described as almost heretical to American forestry: the “founder stand,” in which a small grove is planted and left to grow and seed, over time, an entire hillside.
It is an interesting, scientifically and situationally backed approach. Want to plant trees on your property? Want them to thrive and produce a diverse habitat? Maybe the cluster approach would work well for you.
Choosing a native tree and shrub combo, along with some grasses and flowers will produce a haven in an otherwise stark, or conversely, cluttered, plastic landscape. You can have a “hedgerow” of your own filled with birds and butterflies aplenty. What a glorious thought!