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.

Glaucous-winged gulls

musings on an often-overlooked species

These are one of our most common gulls around here, and they are easy to watch, so I thought perhaps it was time that I write something about them. These gulls are bigger than the medium-sized Mew Gulls and the small Bonaparte’s Gull, but about the same size as Herring Gulls, which are also quite common, and Thayer’s Gulls, which come through on spring migration. At least as adults, however, they are easy to distinguish from Herring Gulls and Thayer’s Gulls, because they lack the black wing-tips of those two species. The adjective ‘glaucous’ means ‘gray’.

Young Herring and Glaucous-winged Gulls are much harder to tell apart, but it can be done. These big gulls take three years to reach adult plumage and sexual maturity. So they spend two years in immature plumages, which feature various shades of brownish gray but no black (check a good field guide!).

Thousands of Glaucous-winged Gulls attend the eulachon spawning run in Berners Bay in spring. They swoop and dip down to nab the weak-swimming fish, but they sometimes miss, leaving a fish with puncture wounds. They also scavenge eulachon stranded by an out-going tide or dropped by other predators. In our study, adults were more successful at catching fish than immature gulls. Young birds gathered in small gangs on sand bars and chased more successful foragers in attempts to steal a fish. However, their attempts at pirating fish from other birds were not very successful, even when the victim was a smaller kind of gull. Indeed, the immatures were notably poor at pirating fish from other birds, and would have garnered more fish if they had caught fish from the river for themselves.

Other species of gull are there too, all gobbling up the fat-rich eulachon. Adults of all species were about fifty to sixty percent successful at diving for their prey. The big gulls could swallow the fish quickly, reducing the risk of another bird stealing the prey. But the little Bonaparte’s Gulls often had trouble swallowing a fish, especially the larger male fish. The longer handling time meant that these gulls were more likely than the bigger gulls to lose their fish to a pirate.

All kinds of gulls gather at salmon runs in summer and fall, but they tend to forage in different ways. For example, at pink salmon runs in Juneau, adult glaucous-wings foraged more often on carcasses than did immatures, and immatures were more often seen feeding on loose and drifting eggs. These eggs were doomed in any case, because they were not buried in the gravels to incubate. Adult glaucous-wings occasionally pulled live salmon from the stream, poking initially at the eyes or at the vent area to force extrusion of eggs. Neither age class foraged much on intertidal invertebrates.

In contrast to the adult glaucous-wings, the medium-sized Mew Gulls fed mostly on invertebrates in the intertidal rockweed and to a lesser extent on salmon eggs. The small Bonaparte’s Gulls foraged mostly on eggs, and less frequently on intertidal invertebrates.

In winter, there are often quite a few Glaucous-winged Gulls in Auke Bay and the downtown harbors. There they forage on whatever they can catch, including larval fish (?capelin), shellfish, and sea stars. A sea star seems to be mostly bony plates and very little soft tissue, so I wonder just how much nutrition a gull can extract from eating one. I also wonder if some of the sea stars that are missing one or two arms might have been assaulted by a big gull. Sometimes, however, these gulls are reported to swallow whole sea stars; this process apparently takes a considerable time.

Photo by Bob Armstrong

Opportunistic foragers, the big gulls can also be found picking bits of meat off discarded deer carcasses on the beach and scavenging whatever looks edible at the dump. Sometimes they pirate mussels from scoters, and swallow them shell and all. They hang around our grocery store parking lots with the ravens, hoping for a handout or some goodies in the back of a pickup truck.