A Gustavus winter walk yields insights about clams, gulls and more

The sea star held by this gull is larger than the one we watched, but it too went ‘down the hatch.’ (Photo by Bob Armstrong)

The good snow was long gone, leaving only some soggy snowplow berms along the roads, where moose and wolves had left their marks days ago. Our usual occupation on winter walks is finding animal tracks and stories in the snow, but that was obviously not a possibility on this December visit to Gustavus. However, if you turn two curious naturalists loose on the landscape, some things of interest are bound to be discovered.

 

Here are some of the small things that captured our attention:

• A long series of humps atop the beams and pilings of the fuel dock turned out to be hunched-up great blue herons, pretending to be gargoyles. There were seventeen of them (!), not the record number for one sitting (the record is more than twenty), but nevertheless a lot of gargoyles.

• A small flock of white-winged crossbills, calling to each other and flitting from one shore pine to another, sampling the cones. Each bird worked on a cone from above, reaching down over the base of the cone and concentrating on the scales close to the tip of the cone, prying open the scales with the crossed bill and extracting the seed. They didn’t spend much time on any one cone but moved quickly on, to sample another one. Were these cones not good providers of sound seeds?

• Beach rye had produced a good seed crop and many seeds had fallen to the sand from the full seed heads. Up north, snow buntings are reported to glean the fallen crop, but who eats them here? The next big tide is likely to wash them all away.

• Piddocks are clams with distinctively curved shells that bear an elongate, flat projection on the inner surface of the shell. That projection serves for the attachment of muscles that are used to torque the whole clam when it burrows into clay or rock. A burrowing piddock can disarticulate its two shells, anchor itself to the substrate with a sucker disc on its foot, and rotate while the two separated shells scrape their way along. Small teeth on the edge of the shells do the grinding (do they sometimes wear out?), possibly with some assistance from chemical secretions. Piddocks are said to live in their burrows their whole lives, enlarging the burrow as they grow. Gustavian beaches are littered with these shells, but I have not found them in Juneau. Why?

• Brown creepers typically forage by hitching up a tree trunk, probing crevices and lichens for small insects and spiders. We found one doing just that, then flying to the base of the next tree and starting upward on that tree. They typically nest behind loose flaps of bark on dead and dying trees, seldom using any other kind of nest site; the bark flap conceals the nest and protects it from severe weather. Once a pair of creepers finds a nest site, they build a little hammock of small twigs and fibers behind the loose bark, and then build a comfortable nest cup of fine materials on the hammock. My friend had found a nest last summer while the adults were feeding chicks, so our curiosity led us to haul out a ladder and climb up to peer behind the bark flap, but the soft materials making the nest cup had disintegrated, leaving just a pile of small bits. The rather specialized nest site makes me wonder how common those favored nest sites might be, and if the distribution of nesting brown creepers might be governed by the availability of good nest sites.

• On the Gustavus dock, several glaucous-winged gulls had harvested sea stars on a low tide, as they often do. We saw one fly up to the dock with a four or five inch sea star in its bill and wondered just how the gull could eat that stiff, prickly, thing with arms sticking out in all directions. So we watched. The gulls repeatedly dropped, then picked up, the star, then finally picked it up and just held it for a long time, with the star’s arms poking out from both sides of its bill. Now what? Well, after almost ten minutes, that sea star simply disappeared down the gull’s gullet. The star must have eventually relaxed, so that the arms folded a bit, allowing it to pass through the gull’s throat and make a big lump in its crop. Even a relaxed star must scratch uncomfortably on the way down. In any case, how much of a sea star is digestible…what makes them worth eating?

Thanks to Dr. Aaron Baldwin of the Alaska Department of Fish and Game for helpful consultation about piddocks.


• Mary F. Willson is a retired professor of ecology. “On The Trails” appears every Friday. Her essays can be found online at onthetrailsjuneau.wordpress.com.


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