Wednesday, May 15, 2013


We often think of vultures as big, ominous-looking birds sitting around the carcass of a lion-killed wildebeest in Kenya or lined up on rooftops next to a garbage dump in South America. But we have our own carrion-eating vulture in the Pacific Northwest, the Turkey Vulture (Cathartes aura).

Turkey Vultures occur throughout the tropical and temperate parts of the New World, from southern Canada to Tierra del Fuego. Those at the northern end of the range, in Canada and northern US, are migratory. Tremendous numbers of Turkey Vultures migrate through Mexico and Central America. The vulture migration over Panama in October has almost reached the status of a tourist attraction, as the birds wheel and climb above the high-rise towers of Panama City in the fall, along with Swainson’s and Broad-winged Hawks.

They return to Washington from their tropical wintering grounds in late March and April to occupy nest sites on cliff ledges or in broken-off hollow trees or other dark recesses, usually in remote areas well away from human disturbance. They lay 2 eggs that they incubate for about 40 days. The young remain in and near the nest for up to three months after hatching. Oddly, although commonly seen in the air, they are almost never seen at road kill, very different from the situation farther south.

These vultures are very often seen early in the morning perched with wings outspread, apparently to dry them out. Why this is so common in vultures and doesn't occur so much in other large soaring birds may be a mystery we never solve.

Turkey Vultures fly with their wings held up in a dihedral angle, which it turns out adds stability in turbulent air. They often fly close to the ground, so this is of great importance. As a wind current hits one side, that wing tilts up and the other down. As it tilts down, it approaches the horizontal, where lift is maximal, and that stabilizes it. Watch a vulture in windy conditions and see how it tilts from side to side.

Unlike most other vultures, Turkey Vultures have a well-developed olfactory sense. Field experiments have shown that they can find something as small as a dead mouse by its smell, even under a closed forest canopy. Watch a Turkey Vulture quartering on the wind, going back and forth as first one nostril and then the other picks up the smell of a carcass from upwind. By going back and forth as the smell gets stronger and weaker, they eventually home in on the spot.

At lower latitudes, where Black Vultures are abundant, they may use Turkey Vultures as their carcass finders, watching individuals of the other species and following them to the ground. The Blacks are also watching each other, so the stimulus from a descending bird spreads outward, probably for quite a distance. Blacks dominate Turkeys, so the Turkeys must be quick to take advantage of a “fresh” meal. In the forested tropics, the much rarer big white King Vultures may finally appear and scatter all the lesser birds.

Turkey Vultures have actually increased in the PNW in recent years, for reasons unknown. Are there more dead animals now? Are they being more successful on their wintering grounds? Were they reduced by DDT like so many other raptors and are still recovering? In any case, they are masters of the air and a pleasure to see in the sky.

Dennis Paulson

Tuesday, May 7, 2013


In the Miocene, about 17 million years ago, great lava flows spread across the interior of the Pacific Northwest, year after year and flow after flow, reaching depths of 6000 feet in some places. As the molten rock cooled, it left very extensive areas of basalt. Some of these rocky areas remain as cliffs, too steep to support soil. In the flatter areas, breakdown of the bedrock produces shallow volcanic soils supporting steppe and shrub-steppe habitats.

Where the soil remains shallow and rocky, there is a rich and diverse plant community, often dominated by scabland sagebrush (Artemisia rigida) and grasses. Even though they remain hot and dry for much of the year, in the spring these lithosols come alive with wildflowers, as do the sandy soils around them dominated by big sagebrush (Artemisia tridentata).

Two of the most showy lithosol species are Simpson’s hedgehog cactus (Pediocactus simpsonii) and bitterroot (Lewisia rediviva). Both of them can be locally abundant on rocky soils in the Northwest interior, adding splashes of pink or red to a landscape that features all the flower colors of the rainbow.

The cactus is typical of its group, with a deep taproot that gathers limited water and nutrients, a succulent stem protected from herbivores by fierce spines, and no leaves. The showy flowers are produced in spring when the bees that pollinate them are most likely to be active in this hot, dry environment. Many other small insects feed on the pollen and/or nectar but are probably not effective pollinators.

Bitterroot is stemless and leafless, the clumps of flowers growing up from a fleshy taproot that anchors the plant firmly among the rocks. This may be another strategy to avoid herbivory—put most energy into reproduction without supporting photosynthetic leaves that are attractive to plant-eaters. The only thing edible on the plant, the succulent root system, is well protected in the soil, but Native Americans ate it as an occasional delicacy. During the Lewis and Clark Expedition, Meriwether Lewis ate bitterroot and brought back specimens; he was honored by its generic name.

Bitterroot survives without apparent chlorophyll by utilizing CAM (Crassulacean Acid Metabolism) photosynthesis, in which leaf stomata open only at night, when water loss is reduced, to take up CO2 that is then released the next day and converted into sugars by chemical pathways that do require light energy.

These flowers and their habitats are best seen in April and May. As the air heats and the soil dries, this large part of the Columbia Basin seems to retreat back into dormancy.

Dennis Paulson

Thursday, May 2, 2013


Many of the common names given to organisms are descriptive, but sometimes the description is valid for only some of the individuals. Take the Black-bellied Plover (Pluvialis squatarola), for example. Forgetting for a moment that the undertail coverts, which some might take as part of the belly, are snow-white, the males of this species have lustrous black bellies, and in fact almost entirely black underparts.

Female Black-bellied are similar to males but duller above, more brownish in comparison with the males' more spangled black and white look. They also may have some white intermixed with the black of the underparts. Nevertheless, they are clearly black-bellied Black-bellied.

However, this is true for only half the year; the underparts are black only in alternate (breeding) plumage, from April to August or September. For the rest of the year, in basic (nonbreeding) plumage, the underparts of both sexes look entirely white at a distance; brown streaks and bars are apparent at closer range. the upperparts are light brown, with slightly darker markings at this time.

Furthermore, most birds don't get black underparts until they are at least two years old. Juveniles fresh off the Arctic breeding grounds look much like basic-plumaged adults but are a bit darker above, with light markings on the feathers. These birds get increasingly faded and worn during their first winter and spring, then molt into a plumage much like the adults' basic plumage for their second year of life. In their second spring, their plumage is identical to that of the adults.

Even more fun, if confusion can be fun, it takes the birds about a month to molt between these plumages, so there are black-and-white-bellied plovers present during one-sixth of the year. This is mostly in March and September, but not all individuals molt on the same schedule, so these intermediate birds can be present at other times.

One of the most interesting aspects of the plumages of this species is the sexual dimorphism. Males conduct aerial displays on the breeding grounds, so it is understandable why they are black below to be more visible against the sky. But why then should females share the color? They are duller than males, but their plumage change at breeding time is still quite substantial. Perhaps different plumages just function for sex recognition, as they do in so many birds, but then why aren't all shorebirds sexually dimorphic?

Black-bellied Plovers are abundant migrants on the Washington coast and also winter in some numbers, both on the outer coast and in protected estuaries in the Strait of Juan de Fuca and Puget Sound. They are usually in flocks, and an observer with a good spotting scope can study all of these plumages at different times of year.

Dennis Paulson
Nature Blog Network