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.