December bricolage

A female hairy woodpecker visits my suet feeder regularly, and I’d bet any money that she is the same one that came all summer long, as a juvenile, in the company of a male, presumably her father. She learned well from her dad, and she still comes.

One day in mid-December, I spotted her wrapped around the suet feeder, her tail curved around one end as she pecked away at the other end. A sudden fluttering caught my interest, as another woodpecker landed briefly, to snatch a quick bite. The new arrival stayed just long enough that I could see her small bill and also see that she was much smaller than the hairy woodpecker. So there was no doubt about it; it was a downy woodpecker. I’m told that they seldom nest in our area but we sometimes see them in the off-season.

On a gray and foggy day, I turned on to the road by the Pioneers’ Home, where the line of young cottonwood trees is often used for perches by eagles scrounging from the nearby dump. On this day, half a dozen eagles were hanging out on the cottonwood branches. In the fog, the eagles were black, the graceful branches were black, the whole array artistically displayed like silhouettes on a silvery backdrop. Splendid!

A few days later, I wandered down the east shore of Mendenhall Lake, then cutting over to the Moraine Ecology Trail. Some post-holing, some bush-whacking, a wet foot from finding a soft spot in the ice—but the quietness was pleasing. The sound of Nugget Falls and scattered raindrops tapping on my cap—that was it. Aaah—maybe a red squirrel chattering over in the woods. I found a thriving, bright green patch of stiff clubmoss, poking perkily up out of the snow, still bearing immature cones. Surprisingly, there were no hare tracks, but beavers had been busy in a couple of places, packing down a trail between ponds, dragging a few branches over the snow, and starting new cuts on some big cottonwoods. An ermine had bounded from one clump of brush to another. The only observable activity was provided by two small, flying insects, maybe midges.

Seeing those little fliers reminded me of other ‘bugs’ that come out on the snow, at least on days of mild weather (although some caddisflies spend the whole winter as winged adults). Several kinds of arthropods, from many different taxonomic groups, can be active in winter; here are some of them: a variety of tiny flies known as midges are active in winter; most fly about but others are flightless.  Males of a moth called Bruce’s spanworm fly in late fall and early winter, mating with wingless females that lay their overwintering eggs in protected sites such as bark crevices. There are winter-active craneflies that dance in swarms, mostly in fall and spring but also in winter, and stoneflies that emerge in late winter, crawling onto land to mate. A fungus gnat can tolerate very low temperatures because it has an antifreeze protein in head and thorax (but not the abdomen, which can freeze and apparently thus reduce evaporative water loss). The famous iceworm (it’s really a worm, somewhat related to earthworms) lives on glaciers, crawling down into cracks and crevices where the temperatures are said to stay about thirty-two degrees Fahrenheit; so they don’t freeze and can go on feeding on microscopic algae and detritus.

Springtail. Photo by Bob Armstrong

And then there are the springtails, non-insect arthropods, most of which can hop about using a forked appendage on the abdomen. Several kinds can be found hopping or crawling over the snow, looking for microscopic bits of food or dispersing to new places. Their predators are out too, including spiders, beetle larvae and danceflies (see photos). A study of one kind of dancefly found that males swarmed near selected landmarks on sunny, windless days in winter, at temperatures as low as eight degrees centigrade. The males carried captured insects to lure females to the swarm, presumably eventually using the prey as a courtship gift.

A dance fly with a springtail. Photo by Bob Armstrong

Thanks to Bob Armstrong and John Hudson for guidance about winter arthropods.

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Bird tails

I recently watched a brown creeper hitching up a little spruce tree just outside my window. Brown creepers typically forage for invertebrates by moving vertically up a tree trunk, hooking their sharp little claws into the roughness of the bark. They actually hop upward, moving both feet at the same time, while the body is braced by the tail. The two central tail feathers are strong and somewhat pointed, although the outer tail feathers have softer tips. The tail is essential to the creeper’s upward locomotion.

That elementary observation made me think more generally about the tails of birds. Their tails are made of feathers supported by a bony structure comprised of fused tail vertebrae. The feathery tails are obviously important in aerial locomotion and maneuverability; that role has been well-studied and we easily see it when watching eagles or gulls swooping back and forth. But here I want to focus on some particular uses of the tail that have special functions, such as seen in the brown creeper.

Like brown creepers, our wood peckers climb tree trunks by hopping upward while braced by a strong tail. The strong, pointed tail feathers are also very important when the woodpecker is excavating a cavity, bracing the body while the bird hammers away. Three-toed woodpeckers have especially strong central tail feathers, allowing them to rear back on tiptoes and put the whole body behind the strike. In contrast, sapsuckers excavate chiefly by using just head and neck movements, and their central tail feathers are not quite so robust.

Red-breasted sapsucker. Photo by Kerry Howard

Both creepers and woodpeckers molt their tail feathers in an unusual pattern. Most birds are said to shed the central ones before the outer ones. But creepers and woodpeckers keep the central ones until the new outer ones have fully regrown, to maintain at least some tail support for their climbing activities while the new central tail feathers are growing in.

The little aerial insectivore called Vaux’s swift (and its eastern relative, the chimney swift) is unable to perch on twigs. It clings well, however, to vertical surfaces such as the interiors of hollow trees (or chimneys) where it nests. Aiding the vertical cling are its spine-tipped tail feathers that press against the walls, helping support the bird in that orientation.

In other birds, raising and spreading the tail fan makes the birds look bigger. Male turkeys, for example, display their spread tails when they puff up and strut to impress females and other males. A ruffed grouse male raises his tail fan during the drumming display that advertises ownership of the display site and attracts females. Female grouse may use a raised tail fan when defending a brood of chicks.

Some birds have turned tail feathers into sexual adornments. Males of some of the African widowbirds and whydahs have tail streamers several times longer than the body—aerodynamically somewhat disadvantageous but apparently alluring to females. Similarly, males of certain manakins in the neotropics and birds-of-paradise in New Guinea have long, decorative tail feathers with odd shapes useless for flight.  

Ring-necked pheasants, native to Asia but introduced elsewhere, have colorful, long tail feathers that they spread, raise, and orient toward another bird during courtship or intimidation of other males. There are many kinds of pheasants in Asia, often with fancy tail displays… including, of course, the biggest, most famous pheasant of them all—the peacock, a native of India but domesticated around the world. All that beautiful color and shimmer of a peacock’s ‘tail’ display is not made by tail feathers at all! The real tail feathers are dull, stiff things supporting the gaudy display from behind. The display itself is formed by upper tail coverts—body feathers on the rump that have become decorative and long. Perhaps the fanciest true tail belongs to the lyrebirds of Australia. Male superb lyrebirds have huge, ornate tails used in courtship. Some of the feathers are fluffy, some are wiry, and two elaborate ones make the lyre-like shape. Males display on a cleared mound on the forest floor, raising the elaborate tail, and dancing, while mimicking the sounds of many other birds. That display is better seen and heard than just imagined; videos are readily accessible on the internet.

Ecological engineers

We use the word ‘engineer’ in a confusing variety of ways and contexts, but here I mean to refer to organisms that create physical structures or changes in the environment—physical changes that affect other kinds of organisms. The concept is still very broad—one could say (and some researchers do so) that a forest of trees or large kelp, or a tallgrass prairie or an eelgrass bed, produces an environment in which temperature, humidity, air or water currents, precipitation patterns, or soils may be altered, thus affecting many other organisms by providing habitat or access to resources.

However, here I want to consider other ‘engineers’—those that deliberately, intentionally make or modify physical structures for their own purposes, with collateral consequences for other organisms.

The most well-known ecological engineers in the natural world are beavers. By building dams, they impound water, raising the water table, creating ponds, sometimes preventing floods, but also flooding low-lying areas. Although they may instinctively respond to the sound and feel of running water by trying to build a dam, they make deliberate choices about the size and shape of a dam and its component parts; they also maintain their structures continually. Beaver ponds provide good habitat for fish, especially juveniles, aquatic insects, various birds, and certain plants, although they obviously destroy portions of the adjacent area by flooding it. Some dams are hundreds of yards long and some are many feet high, depending on the terrain. A well-constructed, well-maintained beaver dam can last for many years, and its effects on the landscape may persist long after the beavers have moved on: the pond gradually fills with sediment and dead vegetation and eventually turns into a meadow.

Hairy woodpecker at nest–notice the beak full of grubs! Photo by Bob Armstrong

Woodpeckers are engineers too. They excavate nesting cavities in trees; the holes persist for years and are used by other birds, such as chickadees, bluebirds, small owls, and certain ducks, flying squirrels, as well as insects and fungi. Experiments have shown that the density of cavity-using critters in an area depends on the availability of woodpecker-made holes. Woodpeckers known as sapsuckers are doubly active as engineers: their nest cavities provide essential nest sites for swallows in parts of Colorado and the swallows are reported to be absent in forests that lack the sapsuckers. The second engineering function of sapsuckers is their characteristic drilling of sap wells in the bark of selected species of trees, a physical change that alters the distribution and abundance of food resources by other birds (e.g., hummingbirds), squirrels, and insects (e.g., wasps and butterflies). The trees eventually heal the wounds in the bark, so the effects of this engineering feat are less long-lasting than that of the nest cavities.

Terrestrial burrowing critters modify drainage patterns and create micro-terrain that alters plant communities. And there are many burrowers (e.g., ants and termites, earthworms, pocket gophers, moles, badgers, mice, and so on). Prairie dog colonies (before humans plowed up most of the prairies) change soil condition over large areas, which then supported plant communities different from surrounding areas. Their burrows also make nest sites for burrowing owls and refuges for snakes. Kingfisher nesting burrows may sometimes alter riverbank stability, but they also provide nesting holes for rough-winged swallows. Marine burrowers, such as certain molluscs or worms, stir up sediments, dig holes in submerged wood and rock, and change erosion patterns.

Even bird nests can be considered to be engineering feats; carefully selected materials are woven together, creating structures that provide habitat for certain insects and microbes and sometimes for other birds. Most nests are quite ephemeral, disintegrating in a year or two, but that’s not the case for the nests of eagles, for instance, nor for the Australasian birds known as megapodes or incubator birds, which build huge mounds of decaying vegetation in which the heat of decay incubates the eggs.

It has been said that ‘humans are tool-using organisms that specialize in engineering’. We seem to be compulsive engineers. People have been and still are the main agents of environmental change virtually everywhere on the planet. Think of all the dam-building, forest clearing, prairie burning and plowing, mining and quarrying, channel dredging and straightening, water diversions, and whatnot. Historically, much of that engineering has been done without any serious consideration of the ecological consequences, but those consequences have been enormous, long-lasting, and mostly negative for the environment. In recent years, there has developed a small impetus to reduce ecological damage resulting from our engineering, but human gratification usually wins the day.