Wild Ideas: Who made that mark?


Photo by Bruce Jones Pileated woodpeckers are highly animated and always on the move, but Tiger Valley resident Bruce Jones managed to get a shot of one taking a rare break.
Photo by Bruce Jones
Pileated woodpeckers are highly animated and always on the move, but Tiger Valley resident Bruce Jones managed to get a shot of one taking a rare break.

One of the reasons I love to write about nature is that it gives me a great excuse to spend time trying to solve the mysteries with which the natural world abounds. Of course, the more answers I find, the more questions I have.

Lately I’ve been pondering some signs animals have left behind as they go about their business near my house. Common ones include scat, fur or feathers, tracks on the ground, shelter (such as nests and dens) and holes or scrapes in the ground or on trees. I’m often asked, “Who left that mark?” and finding fresh ones recently spurred me to add to find out more about them.

Size, shape and the anatomical part used (beak, teeth, or claws) to make the mark are important keys in figuring out what made it. Looking for one or more of the other signs listed here, as well as knowing what animals eat, where they live and other aspects of their behavior can also help in solving the mystery.

A series of small holes are, in a way, a bit easier to sort out, since they offer a pattern. But a lot of animals excavate, for various reasons. Ground that appears to have been disturbed but the soil put back could indicate an animal cached food or buried its eggs there, while open holes are more likely to indicate an animal was hunting for food or dug up what it had cached.

Canids, from domestic dogs to foxes and coyotes, can sometimes make a mess of a yard as they dig and bite the sod to go after moles underneath. And skunks can make smaller holes looking for insect larvae. One day I observed a skunk racing around my yard, digging small holes everywhere. I guessed it was searching for the larvae of June bugs, judging by the dozens of female beetles that had arrived a few weeks earlier and laid their eggs in the sod. Other beetle species may have done the same, and the skunk may also have been attracted to the many ant, bee and wasp in the yard, offering other protein-packed prey prized by many predators.

Early this fall, a flock of northern flickers was drilling into the sod in my yard, busier than miners during a gold rush. While this is not a behavior normally associated with woodpeckers, Cornell Lab of Ornithology’s All About Birds website notes that this particular species doesn’t peck wood: “Flickers eat mainly ants and beetles, digging for them with their unusual, slightly curved bill.”

Large holes in rotting trees and stumps can be a sign of pileated woodpeckers, the largest of Virginia’s native woodpeckers. The holes they make tend to be rectangular, unique among our woodpeckers. Each hole can be a few inches or more than a foot long, and often run up and down a tree.

As well as tearing up rotting trees, the pileated woodpecker also targets decaying stumps and logs laying on the ground. A tulip tree stump in my landlords’ yard was systematically torn up over a few days last summer by a pair of pileated woodpeckers. I had noticed that the stump had been a great host for several species of mushrooms over the year but insects undoubtedly had also taken up residence within the rotting wood as well. The pileateds were probably looking for nests of their main prey, carpenter ants, but they can also “use their long, barbed tongues to extract wood boring beetle larvae (which can be more than an inch long) or termites lying deep in the wood,” according to All About Birds.

Other, smaller woodpeckers dig holes in rotting trees, too, and may take up where pileated leaves off. Woodpeckers, insects and mushrooms are all important players in breaking down and recycling the nutrients from dead trees and thus are essential to our ecosystems. Another benefit of woodpecker holes is that they can be adapted by other species to serve as condos.

Tiny holes on the sides of human-made structures or in dead trees are most likely made by carpenter bees. These bees, which reproduce separately rather than in colonies, chew a hole in wood, then make a trench at a right angle inside to house their eggs. The holes made by carpenter bees and other insects can in turn attract woodpeckers and other predators, adding to the excavation and the nutrient-recycling process.

Extensive scratches, without holes, on a tree trunk, or sign or utility pole, especially along a trail are more likely the markings of a bear. Bears can also mark by tearing out big chunks with their teeth. But perhaps the most important mark bears leave behind, which we humans are likely to miss, is scent, which carries more information about the bear’s gender, health and other physical characteristics.

The exact reasons why bears mark has “puzzled naturalists and biologists for many years,” according to one University of Tennessee study that aggregated data from several field studies, but social communication seems to be at the heart of the behavior. According to the North American Bear Center, “the majority of this marking is by mature males during the mating season.” At that time, especially, boars (male bears) may be giving a warning to other males or advertising themselves to prospective mates. The height of claw and bite marks likely help convey their size to other boars.

Male deer similarly mark their territory, rubbing their antlers on trees (particularly when shedding the “velvet” on new growth) and scraping the ground with their hooves. They have four major scent glands on their body that help leave scent messages on branches above scrapes on the ground, while leaving more information on the scrapes by urinating on them. As with most male displays, bear and deer leave such marks as a warning to other males, which can help them avoid potentially dangerous face-to-face encounters.

© 2016 Pam Owen