Jan 18, 2012

Where Is Sherlock Holmes When You Need Him?

The natural world is wonderfully, albeit also frustratingly, complex. Sometimes I think it would be great to just know everything there is to know about the relationships among species, not that that's ever likely to happen. Mostly, I find nature's mysteries challenging. Trying to figure them out is more fun than playing the word games I was addicted to as a child.


With no degree in ecology, biology, or any of the sciences that might help, but with some college courses in these subjects, a spotty body of knowledge gained from a life-long interest in nature, and 40+ hours of training as a Virginia master naturalist, tackling even species identification can be difficult for me. Animals, not so much, but sorting out plant species can be beyond challenging. I feel a huge victory if I can sort out one sunflower or tree from another. Get down into the weeds, literally, to try to ID forbs, sedges, grasses, mosses, and other plant divisions with myriad species and subtle distinctions, and I often have to tap more knowledgeable sources.


What's left of a dead tree, or snag, has apparently
provided a banquet for predators seeking the insects
within, but which predators? 

Photo by Pam Owen
Species identification is only one of the mysteries naturalists, professional or citizen scientists, face in learning about nature. Often in my ramblings through nature, I really wished I had the genius, phenomenal memory, scope of knowledge, and deductive powers of Sherlock Holmes—one of my all-time favorite literary characters—to sort out nature's intriguing puzzles. Take two I stumbled onto during walks in the woods in the past week: a shredded snag (right) and a pile of feathers (below). Who was responsible?

The snag (another name for a dead tree) was on the northeast face of the mountain behind my house, a few feet from the boundary of Shenandoah National Park. I put my limited knowledge of nature and power of deductions to bear in trying to figure out how the damage had occurred.


The snag was only about 5 feet high and showed no claw marks above the shredded area, which ended about 4 feet up, so a bear was probably not involved in what was undoubtedly a search for insects in the dead wood. Even in January, Black Bears don't truly hibernate and den up for long except during long spells of severe cold (less and less common here) or if they're female and pregnant. 


No scat or tracks were apparent around the base, so while this doesn't rule out small mammals, such as raccoons and opossums, joining in the feast, I deduced that woodpeckers were probably the excavators. With round holes, Pileateds were probably not involved, so that meant one or more of the smaller native species had done all the shredding.


A pile of feathers mark the demise of a bird, but which species? 
Photo by Pam Owen
Woodpeckers were featured in the other mystery, the pile if feathers my dog found on the Thornton River Trail, also in the park but at the other end of my hollow. While my elderly dog is half deaf and blind these days, her nose still works pretty well, and she about dragged me off the trail (dogs must be leashed in the park) following the scent of something. Carrion is the most likely thing to attract her interest, so I assumed something had met its doom just off the trail. Following the dog, I found a pile of feathers. The feathers' markings looked like those of a woodpecker, but what species? 


A pile of feathers and the head are all that are left of a
Red-bellied Woodpecker  on the forest floor along the
Thornton River Trail, in Shenandoah National Park. 

Photo by Pam Owen
I photographed the feathers and started back toward the trail, figuring I'd check my bird field guides when I got back, when the dog pulled once more. This time she led me to conclusive evidence—the head of a Red-bellied Woodpecker (Melanerpes carolinus). The mystery of the victim's identity was now solved, but what had eaten it? 


Woodpeckers are tree-hugging cavity dwellers and are rarely, if ever, on the ground. With their short legs, they're adapted to navigating tree trunks high in the forest, not hopping around on the earth below. So, unless this woodpecker died naturally and just fell to the ground, it likely was picked off from one of the trees above the kill site.


An live, intact Red-bellied Woodpecker 
Photo by Ken Thomas (KenThomas.us) 
Most mammals would just eat the whole bird, head and all, and there was a considerable bird excrement around the kill site, which indicated that the predator was likely a large bird—a raptor. Woodpeckers are diurnal and usually spend the night in a tree cavity, so likely the predator was also diurnal (not an owl). So, which of the raptors who hunts during the day was the likely predator?


At that point, I could really only guess. The Red-shouldered Hawk (Buteo lineatus) is forest dwelling and, having rebounded from the raptor die-off in the 1960s due to pesticides, is pretty common up here in the Blue Ridge now. The noisiest raptor in the area, I used to hear a pair of them loudly and persistently calling every day at my last house, on a lower but also forested ridge. While globally considered common (of "least concern," according to IUCN), they are considered less common in Virginia but "apparently secure," according to the NatureServe database that tracks the status of species.


A Red-shouldered Hawk Photo by Jo Anna Barber, licensed under the Creative
Commons Attribution–Share Alike 2.0 Generic license.

Red-shouldereds are big (17–24 inches) and also eat birds, along with pretty much anything else they can catch, including small mammals, reptiles, amphibians, and crayfish, according to Cornell Lab's AllAboutBirds website. The website points out another "cool fact": "By the time they are five days old, nestling Red-shouldered Hawks can shoot their feces over the edge of their nest. Bird poop on the ground is a sign of an active nest." While this doesn't mean the copious poop I found around the kill site belongs to this species, I agree that it is indeed a cool fact.

So, two mysteries whittled down, but far from solved, in my mind. However, tackling nature's puzzles is one of the best games around, and every time I take one on, I get closer to understanding the web of life and my place in it.







No comments:

Post a Comment