July observations

an insectivorous squirrel, a piscivorous bear, jostling salmon, and ferny thoughts

–Out of the corner of my eye, I noticed a cottonwood branch twitching strangely. I looked up, expecting to see a bird. Instead, there was a red squirrel, bouncing out along the branch, stopping every so often. When it stopped, pieces of leaf fluttered down to the ground. A squirrel eating cottonwood leaves?? But why by-pass most of them, then? I reached for my binoculars and zoomed in.

I could see that some of the leaf pieces were yellow, not green. Then I could also see that the squirrel was not nibbling on leaf stems or leaf blades but rather it seem to be briefly manipulating each chosen leaf. Aha! Yellow leaf bits falling, squirrel picks only certain leaves…That squirrel was foraging for leaf rollers! This seems to be a good year for leaf roller moths, whose caterpillars use silk to bend leaf blades into protective tubes in which they live and feed. But there was little protection from this hungry squirrel, which cruised branch after branch, foraging all the way on juicy morsels of fat and protein.

Mine was not the only such observation: A naturalist friend observed another enterprising squirrel selecting rolled-up alder leaves. The squirrel noisily chewed open the leaf roll and ate the delicacy within, then moved on to more branches and more leaf rolls.

–It’s bear-watching season on Steep Creek near the visitor center, and one day I saw a yearling about twenty feet up in a cottonwood, in an odd pose with its rear end up and head down. Its hind feet were on one branch and its fore feet were on another, lower branch. Those front feet were deftly manipulating a salmon carcass, adeptly turning it first one way and then they other, occasionally flipping it over. The little bear eventually stripped that carcass down to spine and tail and let these remnants drop. Then it spent several minutes cleaning up its front paws and scampered up another fifteen feet to have a nap.

Young black bears usually separate from their mothers in their second summer. By then, they have learned a good deal about suitable foods and foraging, but they sometimes have a little trouble getting enough to eat. This little guy seemed to be doing just fine. However, it looks to be a rather poor year for berry crops, so it will be interesting to see how yearlings do this fall.

–While I was at Steep Creek one day, I watched the sockeye as the females were tail-flapping to disperse the sediments so they could lay their eggs in clean gravels, and the males were jockeying for position near nest-building females. Breeding males are deeper-backed than females, because they develop a slight hump on the back. The hump is probably a visual signal to other males, making its owner look big and hefty. Male pink salmon commonly develop such large humps that one of their other names is ‘humpy.’ But both sockeye and pinks can use the hump in the same way: when two males are side by side, contending for access to a female, the male with the taller hump leans over the smaller male in a literal put-down.

The first time I saw this behavior was while I was watching pink salmon coming into Sawmill Creek in Berners Bay. The male pinks in that creek seemed to have unusually tall humps, perhaps in part because the accessible part of the stream is quite short and flat, so a streamlined body is not so important. But it could also be partly because competition among males in that stream is, for whatever reason, particularly intense, making a big hump especially advantageous.

It was in Sawmill Creek that I watched a male pink that had such a huge hump that its body was shaped more like a dinner plate than a fish. This male would come closely alongside another male and lean that tall body over the less well-endowed male, forcing the smaller male to lie on its side until it could flap away. Since that time, I’ve seen this behavior several times, in sockeye as well as pinks. It seems to me that this is a form of physical domination, perhaps just short of a direct attack with toothy jaws.

–A friend and I are learning how to identify the local ferns. On a recent walk with that goal, my friend noticed a sizable brown caterpillar on a northern wood fern. The caterpillar was gnawing away at the fern frond, and nearby we saw several other chewed wood ferns. No other ferns on our walk showed signs of insect damage, but a botanist friend recalled seeing severe damage on lady fern on Admiralty Island a few years ago.

Most ecologists seem to agree that, in general, relatively few plant-eating insects specialize on ferns, and ferns get less damage from insects than flowering plants, even though there have been many millions of years for insects to evolve toward eating ferns. So how do ferns avoid heavy damage by insects? One suggestion is that ferns have general chemical defenses that reduce their value as food (just as tannins, for example, make many tree tissues hard to digest) that could be more difficult for insects to overcome than specific toxic defenses such as alkaloids; insects have evolved many specific detoxification mechanisms that allow them to utilize flowering plants that contain toxins.

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