Hairy woodpeckers (Picoides villosus) scaling bark from trees

by Christine Hanrahan

Recently, an FWG volunteer asked if I knew what was causing the bark to be stripped from some of the ash trees in the ash woodlot. I unhesitatingly replied, “hairy woodpeckers,” then immediately qualified that by saying “more than likely.” I never like to state anything categorically, especially when it comes to the natural world. After all, bark can slough off on its own, and no doubt squirrels were inadvertently stripping some of the loose bark as they moved up and down the trees. Nonetheless, I had watched hairy woodpeckers working on these trees and flaking bark off rough-barked trees, such as ash, elm, maple, ironwood and so forth, in many other locations over the years.

A number of decades ago, I assumed that the bark scaling was the work of black-backed or three-toed woodpeckers, as they are known to strip bark rather than bore holes the way other woodpeckers do. But there was an awful lot of scaling going on and I was not seeing either of these fairly rare (to our region) woodpeckers. Then I realized that those two species typically work on conifers. It didn’t take long to find that hairy woodpeckers were the ones responsible for the work on deciduous trees. Since those early days, I have become so familiar with this bark scaling activity that until I was asked about it, I assumed the cause was well-known.

Hairy woodpeckers feed voraciously on wood-boring insects, which in our ash trees, would include the notorious emerald ash borer (Agrilus planipennis), a buprestid beetle. While these woodpeckers will eat seeds, nuts, and some fruit in season and are common visitors to feeders in winter, the primary component of their diet is insect matter, larvae in particular. Arthur Cleveland Bent, who wrote comprehensive life histories of North American birds in the 1930s, said of the hairy woodpecker’s diet: “More than 75 percent of their food consists of injurious insects…” Quoting Prof. F.E.L. Beal, he writes “The largest item in the annual diet of the hairy woodpecker consists of the larvae of cerambycid and buprestid beetles.” Cerambycids are long-horned beetles. Certainly, that is some of what they’d be feeding on in the ash woods.

Given that the trees are decaying, the wood revealed beneath the bark is usually semi-rotten and easier to probe for prey. How the woodpeckers find and extract their food has been written about extensively, and Googling the species should yield some information on this front. But essentially, it is thought that hearing, smell, and touch help them locate prey, which they then secure with their long, barb-tipped tongue. Bent reports that the stomach contents of some hairies reveal bits of  inner bark, so not all the bark falls to the ground!

Today (21 January), while walking around Mile Circle and Hillsdale Park in Rockcliffe Park, I saw at least 4 hairy woodpeckers feeding on ash, maple, and elm trees – all but one of them scaling off the bark. As I stood under one tree, I was amused by the rapidity with which the bark was being stripped. A great shower of the stuff fell on me and the snow below the tree. In other cases, the bark was harder to flake off and took more time. Without exception, all of the many trees I saw with these marks – today and in the past – have been dying. A dying tree can carry on for some years before it truly dies and becomes a snag (a standing dead tree), thus the woodpeckers may, by extracting the destructive larvae, help extend the life of the tree somewhat. What is for sure is that they are not damaging the tree. Bent says, “Evidently the hairy does but little damage by denuding the trees of their bark.” Undoubtedly, some folk may not like the look of the stripped bark, but, as one of the photos below shows, in time, it is barely noticeable.

As best as I can recall, I’ve not seen hairy woodpeckers feed this way other than in winter months, and I also recollect reading somewhere that it is a behaviour more typically found in this season.

So the next time you see trees with their bark scaled off as in the photos below, look for hairy woodpeckers in the vicinity. If you examine the scaled areas closely, you’ll likely see insect (mostly beetle) exit holes, as well as rougher holes where the hairy woodpecker has probed the bark.

One of the photos below, although poor quality, shows the hairy with a piece of bark in his bill, ready to drop it to the ground, and an expanse of just-scaled bark.

Reference: Bent, A.C. 1939. Life Histories of North American Woodpeckers. Order Piciformes. Smithsonian Institution. United States National Museum Bulletin 174.


Overwintering Butterflies

by Christine Hanrahan

Winter may seem an odd time to be thinking of butterflies, but on your winter walk, you may actually be passing a butterfly or two, without knowing it. How can that be, you may ask? Well, our overwintering butterflies frequently find hibernation sites under loose bark of trees or in crevices, cavities, and even caves. I’ve also seen butterflies emerging in spring from the eaves of old buildings.

Many folk find it astonishing that butterflies, which we think of as fragile creatures, can survive our cold winters. Not all butterflies overwinter as adults, of course. In fact, only a few do so in this region, but they fascinate us because of their ability to withstand snow and freezing temperatures. Around Ottawa, Mourning Cloak (Nymphalis antiopa), Eastern Comma (Polygonia comma), Green Comma (Polygonia faunus), Question Mark (Polygonia interrogationis), Milbert’s Tortoiseshell (Nymphalis milberti), and Compton Tortoiseshell (Nymphalis vau-album) overwinter in their adult form. Other species overwinter as adults further south, the most familiar example being the Monarch butterfly which winters in Mexico.

How do these delicate butterflies survive the winter? In a word, diapause. As explained by James and Nunnallee (2011), hibernating adults are dormant “and in a physiological state called diapause, characterized by a lowered metabolic rate and radical biochemical changes. Diapause is different from simple dormancy or inactivity as occurs in butterflies and their immature stages during cool periods in spring and autumn or overnight. It is a rigidly controlled physiological mechanism that is genetically fixed or induced by environmental cues.”

Before hibernating, these adult butterflies fatten up by feeding voraciously, often on rotting fruit and sap. This is no different from what hibernating mammals do (think of bears gorging on food to put on fat for the long winter months).

Warming weather encourages butterflies to become active again, even for just a brief period. During the very early, warm spring of 2010, I found butterflies taking advantage of the warmth in mid-March. Likewise, during the unusual heatwave of mid-March, 2012, when the temperature hit +30, I saw several Mourning Cloaks fluttering around the woods. But when the temperatures cooled again, they vanished until the next warm spell.

The most common species that I see, almost without fail, as soon as we have a few warm days in early spring are Mourning Cloak, Eastern Comma, and Compton Tortoiseshell – sometimes all three in the same general vicinity when walking through woodland sites.

How do other local butterfly species spend the winter? Most do so in the larval (caterpillar) stage, but some overwinter as pupae and some, such as hairstreaks and the European Skipper (Thymelicus lineola) in the egg stage. Just as it seems amazing that adult butterflies can survive our frigid winters, it seems to me equally miraculous that larvae and pupae can withstand the rigours of cold weather.

Last winter (2011/2012), I kept two Black Swallowtail (Papilio polyxenes) in a glass aquarium in my garden shed. I didn’t believe that the seemingly desiccated looking pupae could really become butterflies, but they did. In late April, I brought the aquarium outside into the garden and, on 26 May, a female Black Swallowtail emerged, followed a week later by a male from the second pupa. Like overwintering adults, larvae and pupae also prepare for hibernation. “By changing their physiology, butterflies, or their eggs, larvae, or pupae, are able to survive the winter for months in a state of suspended animation.” (James and Nunnallee, 2011)

Next time you are on a winter walk through a woodland, remember that you may well be passing some overwintering adult butterflies, just waiting for those first warm days of spring to fly once more.

References: James, David G. And Nunnallee, David. 2011. Life histories of Cascadia Butterflies. Oregon State University Press.

Wildlife gardening is not just about native plants

by Sandy Garland

The Backyard Garden at the FWG is meant to illustrate how to garden with birds, butterflies, bees, squirrels, and all the other creatures that live in the Ottawa area in mind. We emphasize native species because we assume those are the plants these creatures are looking for to feed on. But, in a wildlife garden, structure is important too.


The location of our bird feeder is a good example of something we did right. The blue spruce at the left of the photo is not native, but it provides winter cover for many birds and squirrels. It’s close enough to the feeder for birds to flee there when disturbed, but far enough that squirrels can’t jump onto the feeder and gorge on the seeds. I measured the distance earlier and the trunk is about 12 feet from the feeder.

House finches take cover in its branches, red squirrels nibble on its buds in spring, and juncos hop around under the tent formed by its lowest branches.

The bare tree at the right of the photo, which is a bit farther from the feeder, is a serviceberry – a horticultural variety of a native species. At this time of year, cardinals and woodpeckers use is as a stop on their way to the feeder. In spring, its blossoms attract early bees and other insects.

Chickadees, which are the most common visitors to the feeder, tend to fly back and forth from the cedar hedge behind the spruce or from the Joe-Pye weed stems off to the left out of the photo. Between sunflower seeds, they seem to find something to eat on those stems, which we leave standing over the winter.

Food, water, shelter, and sites for nests and other homes constitute the elements of a wildlife garden. In winter, food and shelter are extremely important, so try to make sure your garden contains both.

More info:
All about feeding birds
Creating a safe garden for birds