More August Observations

jumping mice, and the gift of salmon carcasses

Fall came early this year—the August rains seemed endless. I returned from a short hike almost as wet as I’ve even been (barring a swim or a nice hot shower). The creeks and rivers were ‘on a tear’, roaring along full of sediment, branches, and logs. Flattened grasses showed where the water had recently been even higher.

On the way home, I stopped at the grocery store. When I checked out with my purchases, a young gal offered to carry out my bags. I said “You don’t really want to go out in THAT!” She said, with a smile, “We live in Juneau,” as she picked up my bags. Good on ya, gal! (But I did carry my own bags out to the car, after all.)

An interesting, but sad, finding in the middle of the trail one day was a dead mouse. Not any old mouse, mind you. This one had a very long, bicolored tail, unusually large hind feet, huge ears, and magnificent whiskers. I thought it was a young jumping mouse, which I’ve never seen alive around here, although they are known to occur in Southeast. It was very thin and may have starved or drowned when its habitat got flooded. (However, the Museum experts said I was wrong—it was just a Keen’s deer mouse. Sigh. But I’ll tell you about jumping mice anyway!)

There are two species of jumping mouse in Southeast, but they are difficult to distinguish. Typically, they live in meadows, wet shrubby areas, and near marshes, and they eat bugs, fungi, and seeds. In summer, they build globular nests on the surface of the ground in tall grass or near small shrubs. They are said to be active only about three months of the year. They hibernate for about nine months, but reportedly many of them, especially the smaller individuals, die before the next summer if they don’t put on enough fat to last through the long winter months.

Near our backyard glacier, bears were actively foraging on sockeye, strewing partially eaten carcasses over the landscape. A yearling fled up a cottonwood when a big bruiser of a bruin approached; the youngster hissed and huffed from its refuge, but soon settled down for a nap.

On the ground near the viewing platform were many carcasses in various states of decay. One had been host to a teeming mass of fly maggots two days earlier, but now it lay limp and mostly decomposed. The maggots were dispersing into the surrounding mats of grass and moss (packed down by bear feet), presumably in search of pupation sites, where they could transform themselves into flies.

Many of the maggots never made it. A juvenile robin appeared and nabbed them one by one, working over several square yards of matted vegetation. The robin foraged repeatedly over the same area, getting more maggots with each pass. She captured several dozen juicy little bits of fat and protein in just a few minutes. A sibling joined her and foraged in the same area, but the first bird had the best pickings.

Photo by Bob Armstrong

Two juvenile Lincoln’s sparrows were maggot-hunting near another rotting sockeye, with much less success than the robins. Other small creatures come to capitalize on the fishy bonanza—juvenile hermit thrushes, a young varied thrush, a pine siskin, mallards, voles, and shrews. Nothing gets wasted, even in the absence of eagles, gulls, ravens, and crows, which scavenge carcasses on lower stream reaches. The surviving maggots make more flies, which nourish next year’s barn swallows (which nest nearby), warblers, and occasional flycatchers. Anything left gets leached into the soil, to fertilize the vegetation and, eventually, the stream. Research, both here in Juneau and in British Columbia, has shown that more birds nest near salmon streams than near streams that lack salmon runs, suggesting that the vegetation is more lush or that insect prey is more abundant around salmon streams. It could be said that salmon fuel the natural economy of Southeast.


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.

An early autumn

Leaves and flowers, fish, mammals, and birds in transition

Fall came to Juneau in mid August. Cottonwood trees began dropping yellow leaves and alder leaves browned and shriveled. The air felt different, and it smelled different, too. On fine, sunny days, clouds of fireweed seeds, floating on their white parachutes, filled the air and collected in windrows on the shores. Mushrooms appeared all over the forest, as if from nowhere.

The grasses and sedges in the coastal meadows slowly changed from green to yellow and gold. Although the splendid pink flowers of fireweed were gone, the stems, leaves, and pods still filled fields with pink and red.

At mid elevations, a few fireweed stalks still bore flowers and some had, in fact, just started to bloom. But the deer cabbage leaves already showed yellow and orange and russet. As the rains increased, the once-fluffy heads of cottongrass drooped dismally, like small mop-heads. But there seems to be a bumper crop of highbush cranberries, glowing brilliant, translucent red (slightly less ‘bumper’ now, after my visit…).

Flocks of robins scoured the roadsides for grubs and worms. In Sheep Creek valley, robins, varied thrushes, and whole families of fox sparrows foraged on elderberries. Near Steep Creek, dozens of warblers flitted from bush to bush. Most were yellow-rumped warblers in immature plumage, but the flocks included several ruby-crowned kinglets and occasional Townsend’s warblers and orange-crowned warblers. I was interested to observe the reactions of the crowds of visitors who waited, mostly impatiently, for a bear to appear. Almost none appeared to notice the many warblers that flew back and forth across the creek and gleaned bugs from the shrubs.

If the bears were occupied elsewhere, many folks enjoyed watching porcupines—studies in slow motion. There were several small ones (known as porcupettes), born last spring, that frequented the Steep Creek area. They were now largely independent of their mothers, foraging on their own and growing perceptibly from week to week. Sometimes one would spend several days in a single cottonwood, taking long naps in between sessions of shredding and skeletonized the leaves. We watched one chomping on willow leaves for a while and then wandering to the creekside, where it avidly consumed dwarf fireweed and then drank from the creek.

The sockeye run in Steep Creek dwindled dramatically during the last two weeks of August. The few remaining pairs of salmon were attended by lots of Dolly Varden, which eagerly line up behind a spawning pair. Dollies, young coho, and sculpin all love to gobble up loose salmon eggs.

Foraging bears left partly eaten salmon carcasses on the streambanks, and it wasn’t long before the flies found them. Soon some carcasses were squirming with hundreds, maybe thousands, of fly larvae (maggots). I was initially surprised to see a bear lick up a pile of maggots and then show one of her cubs the tasty little morsels remaining from her snack. On second thought, however, there should have been no surprise, because bears eat grubs and ants and bee larva when they can. But this was the first time I observed bears eating maggots instead of salmon.

A family of well-grown mallards, still accompanied by mama, foraged regularly in the creek. They scarfed up unburied salmon eggs, enjoyed a snack of maggots on old carcasses, and enthusiastically ate fresh salmon meat when a bear abandoned its catch.