Notes from Gustavus

piddocks, creepers, and a phenomenal feat of swallowing

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 over 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 cone 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?

Photo by Bob Armstrong

Thanks to Dr. Aaron Baldwin, ADFG, for helpful consultation about piddocks.

Walking Gustavus beaches

predator leavings, big snails, and boring clams

A recent walk with two friends on some of the great sandy beaches of Gustavus provided several observations of interest. The four-footed friend probably had the advantage of us mere humans, because she could sniff many messages that were beyond our ken. Nevertheless, the curious-naturalist humans found much to see and discuss.

A line of wolf tracks followed the upper edge of the sand, steadily headed…somewhere. One huge wolf scat held remains of a murre, probably scavenged from a carcass, and another was made up mostly of clay, with a few feathers. Do wolves self-medicate with clay, as some birds do (to counter toxins in their food)?

There was evidence that predatory birds had feasted on murres, mallards, and a loon. Owls and eagles undoubtedly accounted for some of these avian remains. But also, perched on a log within distant binocular range was a slim, gray bird that we thought might be a peregrine falcon. Some owl pellets held the bones of voles, including skulls with teeth, which made identification of the prey relatively easy. A set of vole molars looks, on the grinding surface, like a row of tightly packed triangles; this is quite different from the cusped molars of deer mice, for example. Perhaps I needn’t have bothered to look closely, though: I was interested to learn, from a well-known naturalist in Gustavus, that deer mice are scarce over there, for reasons undetermined.

Scattered along the sand were several strongly ridged, giant snail shells, the biggest whelks I’ve ever seen. These specimens were four or five inches long, but they are said to reach a length of seven inches or so. They belong to the genus Neptunea, but the species name is still undetermined, thanks to some taxonomic confusions. They hang out in the sediments but emerge to travel, feed, and lay their eggs. Neptuneas make their living by drilling (with their file-like radulas) into the shells of other molluscs and slurping out the contents, eating polychaete worms, and by scavenging dead and dying critters. Females produce masses of egg capsules that are spread over rocks and in rocky crevices. Each capsule contains about two thousand eggs, but many of these are not fated to become juvenile snails, because they are eaten by their siblings. After developing inside the protective capsule for many months, well-fed young snails emerge.

Clam shells were everywhere, mostly horse clams. But on one beach we found deeply arched clam shells, each with a pronounced internal projection, for muscle attachment, near the hinge. This beast was entirely new to me, so my learning curve took a jump. These clams are called piddocks (Zirfaea pilsbryi). Piddocks and some other bivalve molluscs burrow into the substrate using their shell as augers; piddocks make their tunnels in clay, sand, or even rock (!). The sharp, jagged teeth on the front part of the shell slowly rasps away, back and forth, as the piddock rotates, eventually making a full circle, only to start over on the next round. Their tunnels can be over a foot long, so their siphons (or the so-called neck: the paired tubes, one of which is used for breathing and drawing in food particles, and the other for excreting wastes) are substantial. If the piddock is eating well and grows as it slowly burrows, the first part of the tunnel becomes too small for the clam to back out, and it can only go forward.

Piddock (Zirfaea pilsbryi). Photo by K. Hocker

I am not a marine biologist of any sort, but I love finding out more about this unfamiliar world.

A quick visit to Gustavus

…a change of place

When the ferries are running, it’s an easy ride to Gustavus: about four and a half hours, usually, with chance of seeing Dall’s porpoises and other marine critters. The ferry often has a Monday-Wednesday schedule, which makes a quick two-night visit quite possible. The great, wide sandy beaches over there are a big draw; they offer a very different habitat from anything here in Juneau and therefore the possibility of seeing different animals, and it’s easy walking, too.

I made a visit there in mid-January. My naturalist friend had set a trail camera at a place where moose habitually cross a wet ditch, carving deep, narrow trails in the banks. The camera captured plenty of moose images, including mamas with calves. One image showed a very odd thing down in one corner, and for a long time we couldn’t figure it out. Then my clever friend got it: ‘twas the rear end of a duck, dabbling in the ditch in the dark of the night. All we could see was an end-on view of the tail with crossed wingtips above. Very odd-looking, indeed.

Out on the grassy flats where spruces have begun to colonize, we found owl pellets, probably of a short-eared owl, containing tiny mammal bones and a shiny beetle. We noticed that clumps of young spruces often seemed to grow on low mounds, where drainage might be better than in the swales. But do they need to grow on these slightly elevated places? Apparently not, because we found a number of very small spruces getting started in the low spots. So maybe a clump of little trees makes its own mound when needles and twigs are shed, or the branches intercept wind-driven dust and silt??

On the sandy beach, we enjoyed following the tracks of a raven fossicking in the tidal wrack and digging up some treasure from the wet sand. There weren’t many mollusk shells left below the high tide line, but I did find one nice piddock shell; just one, though, a contrast with last summer when there were many. Piddocks are burrowing clams, with a jagged edge on the shell for scraping a way into wood or packed sand or even soft rock. Other shells were scarce too: a few whelks in good condition, and some cockles and ordinary clams.

We made a brief foray into one of those long meadows that eventually drain out onto the beaches. Moose tracks going every which way, of course; moose are really common over there. Wolves had gone single-file as they entered the meadow and then fanned out, leaving their big paw prints on the way to the beach.

A rivulet that meandered through the meadow had some open water, despite the recent low temperatures. Peering down into the openings of the ice, we could see amphipods, caddisfly larvae, a diving beetle, and a couple of very small juvenile salmonids that quickly dashed for cover. The water temperature couldn’t have been much above freezing, yet all these critters were active.

We returned to the car on a game trail through the woods. Many critters used this trail, at least in places: moose, wolf, coyote, and best of all, a wolverine that had gone from the trail to the meadow, leaving nice clear footprints. Later, we went back to set the trail camera in this area and hope for some good videos. Along the road, we chanced upon a flock of pine grosbeaks, busily foraging on seeds (more on this next week).

Photo by Cheryl Cook

Back at the house, looking out on a bend of the Salmon River, we were treated to a small parade of trumpeter swans: a pair of adults, then another pair with a handsome gray cygnet. They pulled out on a gravel bar a little way downstream and so gave us a good look at them. An uncommon sight here in winter, although much of the Alaska-nesting population winters along the coast in various places. The swans have the interesting habit of incubating their eggs on their enormous feet, rather than in a featherless incubation patch on the adult’s belly, and both male and female can incubate. Cygnets keep some of their gray juvenile plumage into their second year, becoming fully white-feathered by the next year. Although occasionally they may pair up and start nesting when they are two or three years old, this does not unusually happen until they are about four years old.