The American Three-toed Woodpecker is attracted to trees infected with beetles. Courtesy Wikipedia.
Published Jan. 4, 2006, in the Wyoming Tribune Eagle, “Of birds and beetles. Woodpeckers find silver lining in devastation done by insects.”
2015 Update: Check http://www.eBird.org to see the distribution from year to year of American Three-toed Woodpecker and Black-backed Woodpecker. See http://www.ext.colostate.edu/pubs/insect/05528.html and http://www.fs.usda.gov/barkbeetle. See another post about pine beetle scheduled for next week.
By Barb Gorges
Are they avian ambulance chasers or the feathered equivalent of Red Cross volunteers? Or are they just looking to build a home a short commute from where they can make a good living?
Whichever best describes them, American three-toed woodpeckers and black-backed woodpeckers show up in forests that are under siege from bark and wood-boring beetles.
Not only do the birds make homes in the dead trees, they make meals out of the beetles and their larvae, filling an important niche in the forest ecosystem.
Other woodpeckers in Wyoming, including flickers, sapsuckers and downy and hairy woodpeckers, are fairly common, but the three-toeds and black-backeds are quiet and hard to find.
The Black-backed Woodpecker is one species that enjoys finding pine beetles–to eat. Courtesy U.S. Fish and Wildlife Service.
The three-toed woodpecker can be found in most mountain ranges in the Cowboy State, but the black-backed sticks to the northwest corner of the state and the Black Hills in the northeast.
Outside the state, the range of both species covers forests in much of Canada and interior Alaska plus the Rockies in the northern United States.
Recently three-toed woodpeckers in North America were split into a species separate from those ranging from Scandinavia to northern Japan.
The birds are relatively unknown despite pages of references for studies of three-toed and black-backed woodpeckers listed in “birds of North America.”
Many of the three-toed studies were done in Scandinavia; it isn’t known if the findings hold true in North America.
A relationship with beetles
The three-toed and black-backed woodpeckers both have three toes, two facing forward and one facing, back that help them rise to the challenge of finding wood-boring and bark beetles.
Other woodpeckers have four toes, two facing front and two facing back
These three-toed specialists use a different stance and grip on a tree trunk that gives them greater force in drilling than all but the much larger pileated and ivory-billed woodpeckers.
Other general woodpecker-evolved adaptations are: stiff tails used as props; long, sticky tongues; and skulls with built-in shock absorbers to withstand all the hammering.
While they might make huge holes to find beetles deep inside the tree, the woodpeckers also can scale or peel off the bark to find bark beetle larvae.
The birds excavated a snag, a dead tree, to put their nests in. This takes them a few weeks, but a pair will do it once a year.
Old nest holes then are snapped up by bluebirds, chickadees and other cavity nesters that don’t have the beaks for the job.
In an average forest, there are always a few trees in decline that provide beetles for a few woodpeckers. But then Mother Nature provides a bonanza every so often when wildfire strikes.
Possibly both birds and beetles can smell the smoke. Beetles are on the scene of a fire within a couple weeks and black-backed and three-toed woodpeckers are right behind them.
Steve Kozlowski, a U.S. Forest Service wildlife biologist in Laramie, said three-toeds are normally at such a low density that you are lucky to find one on any given day. But after the Gramm fire near Foxpark in 2003, 14 were seen in one day.
Trees in distress
Even in healthy forests, beetles congregate where a single tree has succumbed to disease, lightning strike or windthrow, said Jeff Witcosky, a regional entomologist with the U.S. Forest Service in Golden, Colo.
Old growth coniferous forests are more vulnerable to beetle kills because young trees have better defenses.
One way beetles might find distressed trees, Witcosky said, is through hydrocarbons known as terpenes that are given off by injured tree tissue. The beetles may be able to sense the compounds with their antennae, he said.
In lodgepole pine forests stressed by drought, mountain pine beetles might randomly land and chew bark before deciding whether to attack or try another tree.
Although there is about one beetle for each species of coniferous forest tree, the different kinds of beetle can be lumped into two main groups.
The bark beetles, favorites of three-toed woodpeckers, lay their eggs just under the bark where they hatch as rice-grained sized larvae that chew little tunnels in the trees cambium, or growing layer.
These traceries in the layer that would become the newest tree ring eventually reach all the way around and prevent sap from moving between roots and needles, killing the tree. When the bark falls off, the tunnels look like shallow etchings in the wood.
The other general category includes all the wood-boring beetles. The larvae of the beetles, favorites of black-backed woodpeckers, eat deeper into the wood. Growing as long as 1 ½ inches, when they reach the adult stage they chew their way back out, fly off, mate and deposit eggs under the bark of another tree victim.
These beetle life cycles can last from one to three years, depending on the kind of beetle. All that time, they are at the mercy of chisel-billed birds that like beetle larvae more than any other insect flesh.
Surrounded by acre upon acre of lodgepole, ponderosa pine or spruce, how does a woodpecker search efficiently for hidden food?
Doug Faulkner, University of Wyoming bird biologist, said it would make a good master’s thesis project to find out.
Do the birds key in on other signs of a tree’s distress? Can they smell the same terpenes that attract beetles?
Jane Dorn, co-author of “Wyoming Birds,” with her husband Robert, said she has heard larvae chewing when she’s close enough to an infected tree. Woodpeckers presumably have better hearing than people.
Populations fueled by fire
Arvind Panjabi, a bird biologist with Rocky Mountain Bird Observatory, spent several years studying the effects of the 85,000-acre Jasper fire that burned in the Black Hills National Forest in South Dakota and Wyoming in 2000.
In the areas of ponderosa pine that burned the hottest, what foresters call a stand replacement fire, black-backed woodpeckers increased tenfold, and peaked the second year after the fire.
Because the Hills are isolated, Panjabi guesses the boost was due to an increase in reproduction rather than the unlikely scenario of birds flying in over hundreds of miles of grasslands.
Because the woodpeckers at a burned area are eating well and are at maximum good health, they lay larger clutches of eggs. But the boom lasts only three to five years.
No one is sure what happens to the increased numbers of woodpeckers if another part of the forest isn’t burning by then.
The bark beetles eaten by three-toeds seem to prefer singed spruce trees. But within a few years these burns lose their appeal and beetles too have to leave for blacker pastures.
Panjabi found that in the Black Hills, numbers of Lewis’s and red-headed woodpeckers in the burn area, though never as numerous as black-backed and three-toed shortly after the fire, continue to slowly increase even when the other two are decreasing.
Sometimes black-backed and three-toed woodpeckers on a new burn have competition in the form of salvage logging of burned trees. They must be harvested within six months or so to make good lumber, but without burned trees there are no beetles and no birds.
To share the bounty, wildlife biologists recommend leaving groups of snags standing. Single snags spread out won’t support these two species of woodpeckers. Neither will clear cuts.
It is important to be accommodating, since without regular woodpecker numbers, normal beetle populations might grow out of hand, forest ecologists say.
Wyoming forests are currently experiencing beetle epidemics too large for woodpeckers or people to control. Beetles are not only attacking sick trees but apparently healthy ones as well.
The only sure control, Witcosky said, will be a long enough episode of extreme cold which will kill the larvae. Winters have been too warm lately.
More about black-backed and three-toed woodpeckers
Despite pages of references for studies of three-toed and black-backed woodpeckers listed in accounts in Birds of North America, there is a lot unknown about them.
Many of the three-toed studies were done in Scandinavia and it isn’t known if the findings hold true in North America.
Also, how did the population of black-backed woodpeckers in the Black Hills become separated by hundreds of miles of grasslands from others in the Canadian boreal forest or mountains further west? It, like the three-toed, doesn’t migrate beyond a little movement south or to lower elevation in winter.
What is the normal population level for black-backeds and three-toeds? Are they normally uncommon species in old growth forest, or are they normally common species in freshly burned forest, a habitat harder to find now than in past centuries?
Dick Hutto, a University of Montana professor of fire ecology and ornithology who has studied the aftermath of the Yellowstone fires, said in an interview in the Missoulian earlier this year that a burned landscape is no less fragile a habitat type than is a wetland.
Presently, the Wyoming Bird Conservation Plan classifies both the three-toed and the black-backed at level 2, at which the primary focus is monitoring. The Wyoming Natural Heritage Database identifies them as globally secure, but rare statewide.
Are these two closely related woodpeckers ambulance chasers? Yes, they do make the most of trees in distress for personal gain. Are they like Red Cross volunteers? Yes, every larvae eaten is one less allowed to live and infect another tree with eggs. Are they Mom and Pop looking for a good place to raise kids? Yes, this drives the behavior of most animals.
So, how do you add one of these elusive woodpeckers to your life list? Find the locations of last year’s forest fires and look for sooty-colored birds on sooty tree trunks. And listen for beetles chewing wood.