DIFFERENT MOLT STRATEGIES

Most birds molt their flight feathers in a fairly straightforward way, as explained in the last blog. The feathers on each wing molt sequentially, starting with the innermost primary and usually ending with the innermost secondary. This is called sequential wing molt.

But there are two other ways to do it.

Very large birds (above about 1 kilogram in weight) that need to be able to fly at all times, for example eagles, cormorants, and herons, can retain feathers for more than one year and molt only some of them each year. The largest among these take about three years to replace all the flight feathers. This molt strategy is called stepwise wing molt.

In many large birds, you can see the different feather generations in an outspread wing because the older feathers are more worn and thus a bit paler. These differences should be evident in this Turkey Vulture wing specimen from the Slater Museum collection.

The other strategy is simultaneous wing molt. If predation is the only reason they need to be able to fly, and birds can avoid predation, they can give up flight for a period of time and drop all their flight feathers simultaneously. This is the case in anhingas, ducks and geese, loons, grebes, and larger alcids, all of which can remain in the water during this period, out of range of their potential predators. Note this group includes the very large swans and geese, which perhaps could not fly very efficiently with gaps in their wings.

The female Mallard is typical of midsummer ducks with all flight feathers missing. The Common Murre also is in full wing molt, usually obvious because the wingtips can’t be seen above the tail.

This Anhinga has dropped all of its flight feathers and most of its tail feathers simultaneously and is in the process of growing them back.

Dennis Paulson

IT'S TIME TO MOLT

All birds have a complex coat of feathers, thousands of them, which they use for insulation, display, camouflage, and flight. Look at a feather closely and you’ll see that it looks flimsy, yet it does its job very well by meshing with others of its kind. Flight feathers can hold up birds such as Trumpeter Swans that weigh in excess of 30 pounds and provide thrust and lift for continuous flight in birds on migrations that extend thousands of miles.

But these feathers, while strong, are not indestructible. Inexorably, a feather wears over its lifetime, and if a bird grew only one coat of them, eventually wear would take its toll. If not naked, a bird would look rather frazzled. Over time the feathers would lose their strength and insulating ability as the microscopic structures that hold them together wore off. Look at the same feather when about a year old, and you can easily see that wear. This Little Gull wing in the Slater Museum collection, from a one-year-old bird just molting into its second set of wing feathers, shows you how worn feathers can become before they are replaced.

The solution to this problem is the annual molt that all birds undergo. All the feathers on the body are replaced each year, usually soon after breeding, which would be in fall in our north temperate zone. Not only are the contour feathers of the body replaced, but all wing and tail feathers are replaced as well, except in the very large birds in which this isn’t energetically possible (see next blog post).

It takes a lot of physiological energy to grow a feather, so molting is a fairly slow process. A complete body molt takes as long as a month for an average songbird. Individual flight feathers take about three weeks to replace completely, so a complete wing molt may take a month or more. These constraints are very important to migratory birds, as they may not be able to migrate until they have finished growing all their flight feathers, and they molt only after breeding, with its own energetic demands, has been completed.

Wing molt is typically sequential. The innermost primary is shed, and its replacement begins to grow. Before it completes its growth, the second primary is shed and its replacement begins to grow. Etc. The molt progresses out the primaries and, at some point, begins in the secondaries, where it moves from the outermost (adjacent to the primaries) inward. This gull is in the middle of primary molt, with the two outermost feathers from the previous generation and the feather just in from those growing in. You can also see that some of the outermost secondaries have been shed.



This adult Black Turnstone shows body molt (worn brownish feathers being replaced by crisp blackish ones) and wing molt (worn brown primaries and newly grown blackish ones, with a gap where the intervening feathers have been shed and are regrowing). Most birds would look something like this in fall.

Of course, in birds that change plumage color between breeding and nonbreeding times, molt of the body feathers must occur twice each year, spring and fall. This molt is one of the most obvious ones to those of us who look carefully at birds. This juvenile Short-billed Dowitcher is just beginning its molt into its dull first-winter (much like adult) plumage; the scapular feathers are often the first to molt.

Dennis Paulson

A CROW FAMILY

It’s not easy to get to observe the development of young birds in a nest, Most songbird nests are hidden away, hawk and eagle nests are high in trees, woodpeckers nest in holes, and ground-nesting birds tend to be precocial, the young leaving the nest soon after the eggs hatch. So when an opportunity presents itself, it’s worth taking advantage of it.

This nest of crows (American Crow, Corvus brachyrhynchos, or Northwestern Crow, Corvus caurinus) was discovered on the seventh floor of a building in the University of Washington Medical School in Seattle. The person whose office was above it alerted Netta Smith to the opportunity, and she brought a camera to work with her many days over the ensuing month to document the development of the crowlets. I was able to drop by on one occasion and watch the action when the birds were about to fledge.

Unfortunately, the eggs had already hatched when the nest was discovered. The average time until young crows leave their nest is about 32 days in the Pacific Northwest, so the eggs probably hatched on about May 1. Thus at the time of the first photo on May 5, they were about four days old. As the month progressed, the young birds looked more and more like crows.

The young developed rapidly with a constant input of food brought by the two parents, which must have had a busy time finding enough for them. Food items seemed to be mostly small and were difficult to identify, but at least some insect larvae were noted. Human garbage likely played a part, as crows in the city forage constantly in dumpsters, but they surely captured “natural” prey as well. No bird eggs or young were seen, but they play a significant part in the diet of crows.

One young disappeared from the nest and was subsequently seen on a ledge several floors below, presumably killed by a fall. This is surely more of a hazard in such a nesting place; tree branches might have stopped its fall. The other four young flourished until, one by one, they left the nest. They tussled with one another as they got larger, and when about ready to fledge, exercised their wings again and again. Netta did not see any of them actually leave the nest, but on one occasion one spent the day on a ledge across the courtyard and was fed again and again. Then they were gone.

One of the most notable things about young crows is their blue eyes. Young corvids often show signs of immaturity by having eye or bill color different from that of the adults.

Dennis Paulson

A BUSY RED SQUIRREL

On July 5, I spent some time watching a Red Squirrel (Tamiasciurus hudsonicus) processing Sitka Spruce (Picea sitchensis) cones at Manning Provincial Park, British Columbia. These small squirrels (around 250 g) are frenetically active and noisy, and watching them is much like watching birds go about their activities.

Two things impressed me about this behavior, persistence and proficiency. The forest floor, in a big grove of spruces, was literally covered with cones. Obviously it was a great cone year, not always the case in any given stand of conifers, and the squirrels were taking advantage of it. This particular squirrel would take only a few seconds to locate a cone on the ground, grab it in its mouth, and carry it up to one of its favored perches on a big fallen spruce trunk.

Fortunately, this was at eye level for me, right out in the open and allowing for continued photography. I don’t know why, but he (it was an obvious male) kept coming back to the exact spot to open the cones. And he did it again and again and again. That was the persistence part. But there is every reason for them to be persistent. When food is abundant, go for it.

Proficiency was also obvious. Each cone was held only for a few minutes, while the squirrel bit off each cone scale and swallowed the seed beneath it. I couldn’t determine whether the seeds were chewed or merely swallowed, as the process was so rapid. Sitka spruce seeds are relatively small (3 mm) conifer seeds, so perhaps they could be swallowed without chewing. However, they also have a “wing” that facilitates their dispersal by wind, so that must presumably be discarded.

In any case, each cone was reduced to its central axis in just a few minutes of manipulating it, the scales falling like confetti in front of the squirrel. It was then dropped, and invariably the squirrel gave its territorial chattering call for a few seconds. then it would hop off the log and pick up another cone and start again.

This squirrel processed cone after cone as I watched. Although Tamiasciurus squirrels are well known to store many of the seeds they harvest to feed on them over the winter, I saw no indication of any caching behavior. Red Squirrels cache bushels of green spruce cones in a single protected spot throughout the summer, and these cones become important when the ground is made inaccessible by deep snow.

When cached by certain verterbrates, some seeds that are stored are lost or forgotten, and they have the potential to sprout into new plants. In some cases (gray squirrels with oaks, nutcrackers with pines), the animal may be as important in the dispersal and reproduction of the plant as the plant is in the diet of the animal. This is not the case with Red Squirrels, which, because they store cones before they open, function entirely as seed predators and not as seed dispersers.

Closer to the coast of the Pacific Northwest, including all of Puget Sound country, it is the Douglas Squirrel (T. douglasii) that typically feeds on Sitka Spruce seeds. It is just as persistent and proficient.

Dennis Paulson

POORWILL, BEAUTIFUL BIRD OF THE NIGHT

Common Poorwills (Phalaenoptilus nuttallii) are widely distributed throughout western North America, but how many of you have seen one? They are strictly nocturnal and perfectly camouflaged in their daytime resting sites.

On a recent early June trip to eastern Washington, we drove up Robinson Canyon, west of Ellensburg, in the evening. Robinson Canyon is a riparian oasis in the midst of sagebrush shrub-steppe and ponderosa pine woodland. We arrived at about 8 pm at a gate in the fence that encloses part of the L. T. Murray Wildlife Recreation Area. As it got darker and darker, we enjoyed the sights and sounds of the local songbirds going to bed. A Western Wood-Pewee sallied after insects later than we expected a flycatcher to be out and about. Another one sang its dusk song nearby.

But we were after more elusive game. As it got dark, our quarry began to stir. At 9:12 pm, a poorwill called its name from the nearby shrubby and rocky hillside. Several others followed in succession, until a steady chorus of melodious ‘poorwill . . . . . . poorwill . . . . . . poorwill’ resounded from the hillsides. At 9:27 pm, we saw the silhouette of a bird flitting across the road. We started the car and pulled away from the roadside at 9:30, when it was entirely dark.

Very soon the headlights picked up a poorwill resting on the road. This bird eats large moths and beetles that it sees against the sky as it rests on open ground, and roads through its habitat often represent the most open terrain for a foraging bird, so we were taking advantage of this long-known way to get a look at poorwills. Their eyes shine brilliant orange in the light of the headlights.

Seven poorwills flushed from the road in the three miles of road we drove, and fortunately, as the goal of the evening was to get photos, two of them remained on the edge as we slowly drove by them, allowing shutters to click to complete satisfaction. The huge eyes, tiny beak (but the gape extends back behind the eyes), and tiny feet (almost useless for locomotion) were visible at close range.

Trying to find them in the daytime is another story. They sometimes perch right out in the open, on broken ground or rocks, but seeing one before you flush it is an art or science that is beyond me. I once chased one around, trying to get photos of it in broad daylight, and I could never see it before I flushed it, sometimes within a few meters. Their camouflage, I thus conclude, is perfect. Joe Marshall, an ornithologist who spent a lifetime studying nocturnal birds, called the Common Poorwill the most beautiful bird.

But poorwills are much more interesting than just being big-eyed, big-mouthed nocturnal insectivores. They were the first bird to be discovered “hibernating,” in deep torpor in a south-facing rock crevice in southern Arizona. Amazingly, this species is still the only bird known to spend long periods in torpor, remaining completely inactive for days during periods of low temperatures during winter. At those times, body temperature can drop to 5°C, oxygen consumption to <10% of normal. This has the earmarks of true hibernation, but it is not. Instead, it is a day-to-day phenomenon, not the deep winter sleep of marmots and other mammals. Poorwills may enter this state at any time of low temperatures, an energy-saving strategy that allows them to cope with periods when no insects are out and about.

Dennis Paulson

BLACK SWIFT, BIRD OF MYSTERY

The Black Swift (Cypseloides niger) is one of the more poorly known North American birds. Seen by most people in flight high overhead, its comings and goings are only poorly documented.

Swifts are aerial insectivores. Their very long wings, with extremely high aspect ratio (length/width), allow them to glide effortlessly or move forward at high speed by rapid wingbeats. They are large enough that their wingbeats are more obvious than those in smaller swifts such as Vaux’s. Not only can they fly for long periods while foraging, but they can fly long distances as well, This serves them not only for long-distance migration (they winter in northern South America) but also for daily foraging trips.

The diet of these birds is of course made up of flying insects. The prey is usually about a centimeter in length or less and may be flying ants, wasps, flies, beetles, leafhoppers or anything else that they can find in the air. Foraging is often very high, beyond the limits of human vision, but during cloudy and cool weather, the birds come much lower, often feeding over water bodies, where insects are usually present even in bad weather.

Because they are such superb fliers, the swifts can wander 80 km or more from their montane nesting areas in a single flight to look for food. They stay away for many hours, accumulating insect prey in a sticky mass in the throat. When they return to the nest, they feed the young by regurgitating this mass a bit at a time.

Nesting is always on cliffs, either on rugged coasts or in mountainous areas, usually behind a waterfall. The nests are built of moss (or moss and seaweeds for coastal nests). Because foraging is an uncertain business if you’re a swift, creating quite a challenge when feeding young, this species lays only one egg. Food delivery must be spotty, even with two parents providing it, as the young takes about seven weeks to leave the nest. Compare that with a nestful of five baby robins that fledge in two weeks!

While censusing birds at Port Susan Bay, Snohomish County, Washington ornithologist Steve Mlodinow observed numbers of these swifts at close enough range to get magnificent photos, perhaps the best ever taken in flight. These photos generated a lengthy discussion about why some birds had white tips to the feathers of their underparts and others didn’t. The consensus, aided by examination of specimens in the Slater Museum, is that the white-scalloped birds are females. In addition, the spotted birds had shorter tails. Sexual dimorphism is quite unusual in swifts, and its significance in Black Swifts is unknown.

Much is to be learned about this species, perhaps not easily. For example, no one has seen Black Swifts copulate; there is a challenge for an adventuresome field observer!

Dennis Paulson

FLORAL EXPLOSION

Spring is a wonderful time of year for the Northwest naturalist. Everything seems to be happening at once. Migrating birds arrive every day. Butterflies add their erratic movement to the landscape. And flowers are everywhere.

The most spectacular flower shows in spring are in the open country and pinelands east of the Cascade Crest. They easily equal the floral spectacle that makes a midsummer mountain hike such a delight, although they are surely less appreciated. But they are worthy of the effort it takes for a Puget Sounder to plan a trip east. Starting as early as March in the sagebrush country, the spring flower show slowly moves uphill with the increasing temperatures of spring and reaches its peak in early May in the grasslands at the lower edge of the Cascades.

Sagebrush buttercups (Ranunculus glaberrimus) and yellow bells (Fritillaria pudica) start off the parade of colors with bright yellow spots in the gray sagebrush landscape. They’re followed by the more conspicuous show of big balsamroot (Balsamorhiza deltoidea) bouquets and wide washes of white and purple phlox (Phlox spp.). Just these flowers alone create a macro-spectacle in that part of Washington, easily viewed from the main highways.

But to see all the phytodiversity you can imagine, get off the highways. Back roads near Thorp or the Umtanum Road southwest of Ellensburg provide as good a flower show as anyone could desire. Drive slowly or walk out through the habitat. Check out open rocky areas for spectacular pink bitterroot (Lewisia rediviva) and Simpson’s hedgehog cactus (Pediocactus simpsonii) flowers and look for the beautiful color scheme of sagebrush violets (Viola trinervata).

And come back about every two weeks to see the turnover, as species after species blooms. You can only hope that there are enough pollinating insects out there to see to the needs of all these sex-starved flowers.

Dennis Paulson