Little winter puzzles

poop parties, shrew tracks, and muskeg mysteries

Early winter walks yielded some small puzzles for curious naturalists to contemplate. Here are a few of them.

Out at Eagle Beach, on a low tide, we observed many crows, mostly foraging busily. Along the tideline, they forage singly, each one slowly walking along the edge of the water, pecking at this and that, and occasionally winkling out something edible.

On top of the sandy berms lay a cap of fluffy snow, much marked by gull feet and the remains of the gulls’ dinners. On the ends of two of these berms, we saw tight clusters of crows, heads down, poking their beaks at something on the snow surface. When we went to inspect more closely, we found that blackish piles of shell fragments, regurgitated by the gulls, had been scattered as the crows sorted through the pile for bits the gulls might have missed. And most of the excreted yellowish splats of digested gull meals were missing their typical lump of solid waste. It seems that the crows had been dining on gull poop.

That seemed a bit strange, with all the small, intertidal animals that would be expected nearby. But the real puzzle was why the crows did this scavenging of gull ejects in gangs. The snowy berms were covered with evidence of gull presence, but the foraging gangs invariably gathered at one end of the berm, leaving the rest unscavenged. What’s the reason for these poop parties?

In a lovely muskeg we found a long trackway of a shrew. It had meandered for many yards on top of the snow, occasionally diving straight down and re-emerging from the same hole. Presumably it had sniffed out something potentially edible to fuel its constant search for more food. But why hunt on the surface of the snow, where the exposed position sees likely to increase the risk of predation?

Later, On Moose Lake, we found another long shrew trackway, extending for over a hundred yards over the snow-covered ice. This shrew periodically dove beneath the surface and came up a few inches farther on. Again, the shrew was travelling in a very exposed situation, and we wondered what made the risk worthwhile—perhaps a frozen insect or two, or some wind-wafted seeds, but what a dangerous place to look for them.

Plonking around on snowshoes in a muskeg, we noticed a small area in which several tiny shore pines had been mauled. The trees barely stuck up above the snow, but each of them had bent and broken twigs with abraded bark and one or two twigs from which the bark had been delicately peeled. No animal tracks were discernible near these mutilated tree-lets. Who was the culprit? ?A vole that tunneled up from under the snow??

That low-elevation muskeg on Douglas was quite familiar territory for me, but my companions wanted to go to the next higher one. So we thrashed through the blueberry tangles and wind-throws for a time that seemed longer than it really was. We didn’t find much sign of animal activity, but on our way back down, we noticed a huge, rounded boulder near the edge of the muskeg. It was snow-capped, but the sides were covered thickly with lichens, so it had been there a good while. We did a mental double-take and realized that we ‘never’ see boulders in muskegs. But why not? If we assume that trolls don’t make a habit of removing them, then what? The glaciers often left erratic boulders, but why don’t we see more of them in muskegs? Does the muskeg (technically a bog) just cover them up eventually? Then why is this boulder on the surface? Is there a rocky outcrop beneath it? I bet some scientist in Juneau can explain this!

Birds in a snowy land

nest-building ravens, cocoon-tearing chickadees, and cockle-dropping crows

In the middle of March, I made a quick visit to Gustavus. It was snowing heavily, so the ferry ride was a ride in white-out most of the way. Good for taking naps (not to mention second breakfast and more than one cup of tea), making up for having to get up early and getting my gear on the luggage cart. A peaceful sort of trip.

Naturalists love to look for animal tracks in the snow and conjure up stories to go with them, but there was so much fresh snow falling that tracks were covered quickly. So animal-tracking was not very exciting, but bird-watching offered compensations.

A thick blanket of powdery snow lay on the ground, and snow continued to fall. But that didn’t deter a pair of ravens. They flew back and forth between a tree behind the house, where they had nested last year, and a flat area just across a small river. Coming back from over the river, they often carried big wads of moss; on other trips, bundles of long strips of plant fiber dangled from their bills.

My friends said that the long fibers came from dead cottonwood trees, so we went over to look. Beavers had felled cottonwoods and willows here, and moose had left the marks of their lower incisors on the fallen willows. On a cottonwood log, the loose outer bark had been pulled away and dropped in small pieces on the snow, and the fibrous inner bark had been peeled off, exposing the bare wood. This was where the ravens had been at work.

The ravens were clearly lining a twiggy nest basket with moss and bark, and lots of it—a cushy bed for the eggs still to come. An eagle cruised up the river and received a rough welcome from the ravens, which escorted it off into the distance. Maybe the ravens were just making sure that this eagle knew there was a no-fly zone here, ahead of the time when the nest would have occupants.

One day we saw a raven flopping about in the deep, fluffy snow—taking a snow-bath. It pushed its head forward into the snow, rubbing on both sides, then vigorously threw snow over its body with flapping wings. Moving to a new, still undisturbed, spot, it repeated the process. I wonder if snow works as well as water, for a bath.

raven-rolling-in-the-snow-1-by-bob-armstrong
Rolling in the snow. Photo by Bob Armstrong

The ravens aren’t the only ones who know that spring is coming. Oregon juncos are singing and the sapsuckers are back from winter quarters. Although magpies are still around and so are slate-colored juncos, these will soon head for the Interior, where they nest.

Other birds were out foraging in the snowy landscape. A little group of pine grosbeaks flitted through the shrubbery, chatting quietly with each other and nibbling willow buds. One of them dropped down to the snow and ate the seeds from a fuzzy seed-head that poked up from the snow at bird’s-eye level. Of course, we had to determine what kind of seeds they were, which led to some discussion and then back to the books. Ah, they were the seeds of big-leaf avens, a fairly common plant of open areas.

Just over our heads, a chestnut-backed chickadee perched on an alder, pecking and pulling furiously at something for several minutes. Finally, it began to extract and eat some bright green bits. After it flew off, our further inspection revealed that the chickadee had found a cocoon stuck to the alder twig. The cocoon was very tough—not easy for us to tear open even with forceps (we had to use scissors), but the persevering chickadee had won the prize inside and eaten all the juicy bits except for the very end of the pupa, leaving a fragment of pupal skin. That was one happy chickadee! We wondered how they learn to recognize insect cocoons as potential food sources.

When the tide went out, we strolled along a snow-free beach; what a relief from floundering in the knee-deep white stuff, too soft for those little snowshoes, typical of our area and never meant for powder snow, to do much good. Here the crows were plucking cockles from the silty sand, flying up a few feet, and dropping them. This is a common behavior by which crows crack open a shell to get at the edibles inside, but it depends on the shell landing on something hard enough to crack it. On this beach, there weren’t many rocks, and the chance of dropping a cockle and having it hit a rock was small. One crow tried two different locations and dropped its cockle sixteen times (!!) before it could eat its prey.

There was a stiff on-shore breeze that buffeted the foraging crows. So, instead of their usual walking gait, they often faced into the wind and side-stepped—just as I used to do when wading a fast-moving stream.

April is the cruelest month

the poet was right

The poet had it right! Although April has often been a benign month here, with lots of sun and rapid warming, this year’s April has (so far) offered us lots of rain and temperatures parked in the forties. Not living up to expectations! Nevertheless, Mother Nature has not forgotten Spring, and things are happening.

The yellow hoods of skunk cabbage are now conspicuous in many damp places, with both male-phase and female-phase flowers available. A little experiment in Washington indicated that the sweet fragrance of the flowering display initially stimulates insect pollinators to search for the flowers, where pollen on male-phase flowers is the chief reward. A more local experiment found that the searching insects land preferentially on displays with the bright yellow hood, rather than those that are still green. The little brown beetles that are the principal pollinators are still scarce (in mid April). But eventually they will appear and come first to male-phase flowers, to feed on pollen and use the inflorescence as a mating rendezvous, and then carrying pollen to female-phase flowers. I have observed that, at any one time, there are usually many more beetles on male-phase than female-phase inflorescences, but on some occasions, there are crowds of beetles on the females too. That pattern suggests that perhaps the females are only fully attractive at certain times, possibly drawing in the beetles by air-borne chemical signals.

rufous-hummingbird-by-bob-armstrong
Photo by Bob Armstrong

The rufous hummers arrived a few weeks ago, one of the earliest arrivals on record. There are rumors that Anna’s hummers, usually just vagrant visitors later in summer, may have overwintered here. If they start to nest here commonly, it will be interesting to see if there is evidence of competition between the two species.

Ruby-crowned kinglets are now cheering human listeners with their rollicking song, even in the rain. I watched a female white-winged crossbill poking about on the ground, selectively choosing certain wisps of grass for a nest lining. In mid April, I heard my first fox sparrow, singing from an alder thicket.

Salmonberry canes with new pink flowers decorated a south-facing upper beach at Auke Rec, and my favorite yellow streamside violets shone against the still-drab forest floor.

Several observations in the Eagle River/Eagle Beach area piqued the interest of a couple of curious naturalists:

–Crows foraged on a mudflat at low tide, finding very small items and gobbling them down. Later, we saw crows exploring the wrack left by a very high tide, extracting mussels and maybe amphipods, and trying vainly to crack the mussels by flying up and dropping them on the too-soft sand.

–An immature herring gull was foraging at the edge of a sand flat, rapidly paddling its feet up and down on the wet sand. This technique was successful in stirring up small organisms, and the gull nabbed one after another. At what age do they learn this mode of foraging?

–There was goose scat that contained seeds of (I think) Canada mayflower, reminding me that geese up on the tundra (and, as I saw, in Tierra del Fuego) commonly eat fruit and disperse the seeds. Geese are generally known as grazers, so this is an added ecological role, shared with bears, thrushes, and some other songbirds.

–A burrow under some tree roots in the sediment bank at the edge of the river had been occupied for some time by a porcupine, which deposited some long white hairs and the usual oval winter pellets (reflecting a diet of bark and needles), as well as more recent, small, dark, round spring pellets (reflecting a shift to soft, fresh, green vegetation). It seems unlikely that the porcupine made this burrow, but it provided a very nice retreat.

–Deer of all sizes had danced on the river sandbars exposed by low-water conditions. We wondered why they spent so much time in that habitat, which offers nothing to eat.

–A little promontory in the river was liberally strewn with the marks of ownership by an otter. There were dozens of small piles of debris, each one topped by a dark, slimy mass. We failed to find a den in this area, although the nearby forest held a number of old, now-unoccupied burrow systems under tree roots.

–As we basked at the river’s edge in some momentary rays, we saw lots of small insects fluttering about. A few landed where we could inspect them, and so we could see that they were stoneflies. Some of them regularly dipped down to touch the water surface, no doubt laying eggs. We wondered how they choose the sites for placing their eggs—what are the cues that indicate a potentially good place?

Fritz Cove

wildlife spotting and speculation along a quiet stretch of highway

It was murky sort of day, low overcast, occasional rain squalls, and sloppy snow underfoot. Our schedules didn’t offer many breaks either, so we opted for an easy walk along the North Douglas Highway.

The beach by the North Douglas boat ramp could well be called our very own ‘Skeleton Coast’ (with apologies to southwestern Africa), for the number of picked-over, disassembled deer carcasses reposing on the cobbles. Two eagles each claimed a deer head, while ravens, crows, and gulls squabbled over the few remaining scraps.

A couple of humpbacks cruised and dove, attended by a small gang of sea lions. Either the whales weren’t stirring up much tasty fare for the sea lions, or they had already provided very well for the ‘lions, which spent a good deal of time lolling about, floating belly-up or side-up, poking out a fin or two occasionally.

We counted nineteen kinds of birds (and there may have been more). All the usual suspects were there. We watched a red-throated loon with a long, wriggly fish, which was finally subdued and swallowed. There were a few Pacific loons and what we thought was an immature yellow-billed loon. A duo of common murres was a nice surprise. The only songbird was a song sparrow, which—around here—could well be called a beach sparrow.

A mixed flock of numerous scoters included mostly surf scoters, some white-winged scoters, and a probable black scoter. The scoters were diving, apparently for mussels. Most of the birds were diving independently of each other, with only a few of their famous chain-dives (in which a whole line of birds all comes up a spot where, one by one, they go down; a little later they all come up, one by one, at another spot a short distance away. I’ve never been able to find out why they do that.)

Several glaucous-winged gulls were hanging out with the scoters, mostly behaving very casually and innocently, floating around together. But every so often, a gull pounced on a scoter that was just coming up with food in its bill. At least some of those pounces made the scoter release its catch, to the benefit of the piratic gull. But many attempts at piracy seemed to fail. More puzzling was the observation that a gull would jump on the back of a floating scoter, forcing the scoter under the surface. Are the gulls trying to make the scoters dive for food or are they just having fun?

A few days later, it was still raining, and blowing, and I stopped at the North Douglas boat ramp. I was attracted by dozens of crows in the parking lot and on the cobbly beach. I pulled up near the far end of the lot, away from the crows, and just sat there to watch what was happening. It soon became clear: the crows were collecting small mussels from the beach, flying up and dropping them on the hard blacktop surface (and on the beach cobbles). By careful watching, I determined that sometimes a mussel shell cracked after one drop, but sometimes it took four drops of the same mussel before the crow could gain access to the soft interior.

crow-with-mussel-by-bob-armstrong
Photo by Bob Armstrong

The height of the drops varied greatly, from about five feet to maybe twenty feet or so, and longer drops seemed to be more effective. But a high-flying crow took longer to descend to its prey, which gave other crows time to sneak in and appropriate it. There were many attempts at stealing food from each other, so theft was a real risk. There was a trade-off between effective cracking and protecting the prey from competing crows.

I would love to know more about the energetics of this behavior. Flying up and then zooming down to protect the food takes energy. If a crow has to fly up three or four times, does the energy in one mussel fully repay that effort? Once a mussel shell cracked, the crows would poke and pry to extract the insides, often holding down the shell with a foot. Can crows wrench out the strong muscle that bivalves use to shut the shell—that muscle is very tightly attached to the shell, or can they only feed on the other organs?

This was also a bathing place for the crows. A pothole in the blacktop had collected rainwater. It was big enough for two crows to fit in at the same time, with much exuberant flapping and splashing. Occasionally several crows would line up politely to have a turn at their public bath. Bathing was not as competitive as feeding!