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Perseverance Trail to Granite Creek

Posted: July 14, 2011 - 3:54pm  |  Updated: July 14, 2011 - 6:35pm
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If one sits quietly, marmots often pursue their normal activities within easy watching distance. This one is doing a bit of grooming, perhaps relieving an itch.   Photo courtesy of Bob Armstrong
Photo courtesy of Bob Armstrong
If one sits quietly, marmots often pursue their normal activities within easy watching distance. This one is doing a bit of grooming, perhaps relieving an itch.

Rains had persisted for days and days, with no end in sight. Nevertheless, a friend and I took off up the trail and, much to our surprise, the sun peeked out and no rain fell until we were home again!

On the way up Perseverance Trail, we noticed a number of rolled-up cottonwood leaves lying on the ground. When unrolled, each leaf revealed a network of silken webbing and a collection of small black pellets, indicating the former presence of a moth larva. The larva had eaten a third to a half of the leaf, digested the tissue and excreted the pellets, and rolled the remainder of the leaf as a protective shell around it while it grew. The trees dropped the damaged leaves, and the larvae crawled into the soil to pupate while then transforming into adult moths that will fly later in the summer.

Margined white butterflies fluttered over violets and buttercups, the white males outnumbering the more dusky females. Although it was now July, songbirds still sang, presumably in the interest of starting second broods of chicks. Fox sparrows were heard most commonly, but there were also a few Wilson’s warblers, yellow warblers and hermit thrushes, and occasionally Swainson’s thrushes, ruby-crowned kinglets and Pacific/winter wrens.

We turned up the Granite Creek trail, crossing deep, soft snow where an avalanche had brought down lots of broken branches. A group of mountain goats grazed in the slopes of Juneau Ridge. Marmots sunned themselves on the rocks, scurried across snow patches and wandered into the underbrush.

Several tiny shrews scuttled across the path. We see them so often that there must be a lot of them! Shrews comprise an ancient group of mammals, originating perhaps forty-five million years ago. They live at an amazingly fast pace. Their little hearts beat 1200 times a minute! And they have to eat almost constantly, so they can never sleep for more than a few minutes at a time. They have very short lives (about a year), and the adults are reported to die after they reproduce.

Shrews eat a variety of invertebrates, including insects, spiders, and snails. They find their prey by echolocation (as do bats). Juvenile shrews have to learn to forage on their own, so growing up is a time of great experimentation for them. I recently learned something fascinating about young shrews: Although the rest of the skeleton is bony, much of the jaw initially remains as cartilage, which is flexible. The jaw bones harden gradually, in response to the bite force needed for capturing the commonest prey in the habitat of the young shrew. Additionally, the muscle pull on the still-flexible jaws determines the proper bone formation for best use of the common prey. So if the young shrew eats mostly crunchy beetles and snails, the jaw develops one way, but if it eats squishy worms and caterpillars, the jaw develops another way. Shrews are unique among placental mammals in allowing the environment to shape skeletal growth.

Also wandering around in the trail were two very young deer mice, surely quite recently out of the nest. One of them took refuge under the raised toe of my friend’s boot — clearly, its mama hadn’t told it to beware of two-footed monsters! These two youngsters were in no hurry to hustle into the trailside vegetation, but scuttled aimlessly around in the trail, so we watched them for several minutes.

For no very good reason, we kept track of how many kinds of flowers were in bloom: over sixty species! And that doesn’t count the grasses and sedges, some of which are quite beautiful and worth knowing, but that’s a real skill that I lack.

The broad, white inflorescences of cow parsnip (a.k.a. Indian rhubarb) attracted many small insects. I fervently wished that I knew more about insects, because there was surely a story unfolding here. There were tiny brown beetles (much like those that pollinate skunk cabbage) and at least six kinds of “flies” of various sizes, the smallest no longer than a millimeter. All of them crawled over the small flowers, sipping nectar and probably eating pollen. In their midst, there was often a wasp or two, also innocently nectaring, but occasionally leaping toward a fly. The flies took evasive action but sometimes the pouncing wasp was successful in nabbing its prey. Another variation of the old story about the wolf in sheep’s clothing.

As we passed Ebner Falls on the way down, we heard a rockfall rumbling downslope toward the creek, well behind us. But our curiosity didn’t extend to going back up to see the result — the horses were headed for the barn, and as we drove home, the rains began again.

• Mary F. Willson is a retired professor of ecology.

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