On tanagers and silverweed

backyard notes, a colorful bird, and a wetland plant

My home pond has been rather quiet lately. Two or three unemployed male mallards loaf around companionably while their females are egg-sitting. Sometimes just one male is there, a female (a late-nester or re-nester) visits briefly, and they forage side by side. But if she comes when two or three males are there already, all companionability disappears and there are serious battles between males. On a sunny (!) day after many days of rain, little fish were rising to the surface; a roving kingfisher swooped down to take one away. Up in the trees, the big treat was seeing a juvenile junco and a juvenile nuthatch, well-feathered, flying, fully competent, but each one still being fed by an attending parent. And out my kitchen window, I saw two really tiny squirrels, frisking about on the tree trunks.

A lucky friend stepped out of her door one day and saw an unusually colorful bird—a male western tanager. The fairly gaudy yellow and black body is topped by a head that’s red or red-orange. I haven’t done a proper analysis but it seems to me that we have fewer really colorful birds than does the eastern deciduous forest, with its grosbeaks, orioles, cardinals, and (yes) tanagers. Western tanagers are not common here. Years ago, my field crew and I were thrilled to find a nest in a thicket at the head of one of the small bays on the west side of Glacier Bay (if I recall correctly).

Photo by Kerry Howard

We live near the northern limit of the western tanager range. They nest all over the mountain west and winter in Mexico and Central America, feeding on insects and fruit. On the nesting ground, they are territorial; both male and female chase away intruders. First-year males can breed but are subordinate to older males, so they don’t get first choices of where to set up a territory. Pairs are socially monogamous; extra-pair activity is little studied. Females build their cup-shaped nests (twiggy on the outside, lined with grass, hair, rootlets, etc.) often on a conifer branch but sometimes in deciduous trees. Males accompany their mates during nest-building and egg-laying, presumably as a guard against possible philanderers. A clutch of three to five eggs is incubated for almost two weeks by the female, who may sometimes be fed by the male. Chicks stay in the nest about eleven days, fed by both parents. Very young chicks are fed mashed up bugs regurgitated by the mother, while the male apparently brings in small whole insects; older chicks get bigger insects. There is usually just one brood per season.

The red, orange, and yellow colors come from carotenoid pigments. This tanager makes its red plumage pigment directly, probably from insects in the diet, in contrast to other North American tanagers, which make their red plumage by converting yellow pigments that are also derived from their food. The intensity of the red on the head varies, perhaps as a result of differences in insects eaten. It is apparently not known if females choose their males in part on the basis of coloration. Many other studies of western tanager life history are reported to be under way, so stay tuned.

Out on the upper tide flats, we commonly see a plant called silverweed. The common name derives from the silky white hairs that cover the underside of the leaves. I found no information on possible functions of those hairs, although it seems possible that they might retard evaporative water loss by protecting the leaf surface. Be that as it may, silvery leaves upturned by the wind made a field of pink shooting stars even more spectacular.

Silverweed flowers are yellow; they may or may not be self-fertile (depending on what source you read). The flower has nectar and is visited by bees, flies, and beetles. It also has stolons or runners that spread out over the ground, and new plants can grow from nodes on the runners.

The Latin name for silverweed is either Potentilla anserina or Argentina anserina—the proper genus is debated. My interest was caught by the diverse explanations for the long-standing species name ‘anserina’. ‘Anser’ means goose in Latin. One suggested reason for relating the plant to geese that the leaves may have reminded someone of a goose’s foot marks. This strikes me as ludicrous, because I see no resemblance whatsoever. Another explanation is that by growing in rock crevices, the plant is safe from grazing geese (graylag geese in Europe). This notion wouldn’t apply here, because the plant grows mainly on flat sediments that offer no protection from geese. The third explanation is that the plant was used (in Europe) to feed geese. This is getting closer to something real—on our upper intertidal meadows, Canada geese regularly dig up and eat the roots. So we find small pits scattered over the flats where goose bills have grubbed up the roots. One final note: near the mouth of Fish Creek, a group of strolling friends found several spots where the ground was littered with dozens of fresh, bright green spruce tips. We had no good way to account for that–a natural phenomenon, maybe wind, or just kid stuff?


Visiting the wetlands

toad ponds, goose foods, and owl pellets

Instead of the more usual approaches via the dike trail or Industrial Boulevard, we went in via the public access off the Mendenhall Peninsula Road–down the slope through the bear-clawed alders, past the deer-nipped skunk cabbages, across a swamp. Under some sprawling roots we found a heap of mallard feathers, where some ground-predator had enjoyed a meal. Off toward the end of the peninsula lie several shallow ponds, where toad tadpoles could be found in summer, but I don’t know if toads still use those ponds.

Finally out on terra firma again, the beach rye was barely beginning to send up green shoots. We could hear Canada geese talking to each other in several portions of the wetland. Where the beach rye thinned out, and especially in patches of some smaller vegetation, there were thousands of shallow divots in the damp soil, along with lots of evidence of goose digestion. We watched a flock of foraging geese for a while, observing that their head motions indicated digging and clipping. Of course, we had to see if we could determine what they’d been grubbing up!

Photo by Katherine Hocker

Near many of the divots we found discarded lumpy rootstocks (if that’s the right word) that often bore a thin green shoot; the tap root was cut off. A few of these green shoots had matured enough that we could discern the shape of the developing leaf, which suggested to us that this favored plant was silverweed. We then sought some intact silverweeds and grubbed them up (my fingernails may never be the same again). Oh yes! It’s silverweed. I tried to pull up some of the taproots and discovered that they are very reluctant to come out of the ground, but the geese can break them off. In the bottoms of the divots we could often see the snapped-off lower part of a tap root, and by looking at the intact plants, we could see that the geese were selectively feeding on the upper part of the taproot, just below the lumpy rootstock.

Our education continued when we consulted Pojar’s book of regional plants. Indigenous people have long used silverweed for food and medicine. In some cultures, the tap root (cooked) was eaten by high-ranking men and the lumpy rootstock was given to commoners. So the high-grading geese knew what they were doing, so to speak, but I have to wonder why they so often rejected the lumpy part. According to other sources, silverweed is also known as goose-wort (even its scientific name indicates association with geese!), because it is a favored food, and we were merely late-learners. A residual question lingered: could the discarded rootstocks take hold and regenerate the plant?

The geese offered us another puzzle too, but this one remains unsolved. Many of the goose feces that were scattered on the ground had a strange look, with lots of short, thin, red bits. So I picked up a few and broke them open. They were full of mashed up green material (no surprise there) and the little red pieces. With the help of a hand lens, we could clearly see that these scats were chockful of moss! The red bits were stems, some still bearing their moss-leaves. Who knew that geese eat moss—and in some quantity!

There were many other treasures to be found by curious naturalists. Feathers of a short-eared owl—taken by an eagle or shot by a human and later scavenged? Feathers of an immature glaucous-winged gull (this took some searching on the internet). Several owl pellets composed of vole bones and fur. Vole tunnels and runways and digging sites, usually deeper than those of geese. Porcupine scat on top of a stump; this is an odd place for porcupines to visit, but we do sometimes see them wandering about in the wetlands. Some of the stray white-to-tan hairs we found could have come from porcupines.

A few days later I returned to this area, this time focusing mostly on the wonderful miniature gardens growing on the old, stranded logs and rootwads. A weather-beaten blueberry shrub, a couple of thriving currant bushes, and a venerable elderberry bush had sent down roots. The diversity of mosses, lichens, fungi, and even slime molds on the old wood was impressive, considering that they are totally exposed to desiccating winds and (sometimes) sun, salt spray, sleet, and pounding rain. I have to wonder how this community of diminutives might differ from that on similar logs and rootwads under the forest canopy; to do this comparison using rigorous science would be very difficult (because of the many different microhabitats on the gnarly rootwads), but a more casual approach could be instructive.