BLACK-BELLIED PLOVERS - NOT ALWAYS BLACK-BELLIED

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

THE SWALLOWS ARE RETURNING

This isn't Capistrano, but our swallows are on their way back from their wintering grounds. The first to come are Tree Swallows (Tachycineta bicolor), which winter in southern US and Mexico. They probably winter the farthest north because they are programmed to migrate so early. In fact, a very few birds sometimes winter as far north as Ridgefield National Wildlife Refuge in southwestern Washington.

Tree Swallows are cavity nesters. But they can't excavate their own cavities like a woodpecker can, so they depend on natural cavities, old woodpecker holes, and nest boxes that we put up for them. They like to nest over water when they can, as predators that can climb trees to prey upon swallow eggs and young don't inhabit flooded wetlands.

Thus nesting cavities for them are quite limited, and there is fierce competition for them among swallow pairs. The earlier a male swallow returns to its breeding grounds, the more likely it will find an unoccupied cavity. Once a cavity is occupied, it's an uphill battle for the next bird that shows up to try to take it over, and so first come, first served.

Thus our Tree Swallows start trickling back to western Washington by late February, and the trickle becomes a river by the beginning of April. By that time, pretty much all available cavities are taken. Of course many of these birds continue on north, all the way to Alaska.

This surprisingly early arrival, well before our real spring, comes with a downside. The weather can be wretched at this time of year, cold and windy and rainy. Swallows are aerial insectivores, and their prey can be very hard to come by under such conditions. There is no doubt that in an especially bad spring, some of the birds succumb to starvation. There is no point in trying to raise a brood of young until conditions get better, so they don't attempt that until considerably later, some time in April or May.

Male and female Tree Swallows look the same, beautifully iridescent blue above and snow-white below, but with an interesting caveat. First-year males look just like older birds, but first-year females are recognizably different, dull brown on the back. There are scarcely any birds in the World with a unique first-year female, but the Tree Swallow is one. The adaptive significance of this first-year plumage is poorly understood.

Dennis Paulson

THE COMMON SEAGULL

Seagull? Everyone knows what a seagull is, but why do we use that name for them? They are gulls, GULLS. We don’t have “seaducks” or “sealoons” or “seaterns,” so why “seagulls?” I don’t know, but I’ll never stop asking that question. Although all of them visit the sea for at least part of the year, more than half of the gull species breed on fresh water.

On Puget Sound, there is one very common gull, the Glaucous-winged (Larus glaucescens). In winter, most of the large gulls you see are Glaucous-winged, just as most of the small gulls are Mew Gulls. A moderate variety of species make up the other few percent.

Although in winter they wander inland to near-coastal freshwater lakes and well up the larger rivers, Glaucous-wings are basically marine birds. They breed throughout the protected marine waters of the Pacific Northwest in good-sized colonies on islands and scattered as single pairs at ferry docks or on rooftops. On the outer coast, the Glaucous-winged is replaced by the Western Gull as a breeding species.

Each pair nests in a scrape on the ground, lined with grass, twigs, and anything else that can be found in the limited nesting territory. The female usually lays three eggs totaling about 10% of her body weight, the last egg laid a bit smaller than the others. Both sexes alternate incubation for a period of about 27 days. Hatching takes a surprisingly long time, 2-3 days from pipping (first crack appears) to completely out.

The adults quickly begin to forage for the young, foraging trips lasting several hours. Prey items are brought about 10 times/day to a nest of three young. The young grow rapidly and are able to fly at about six weeks of age. They typically leave the colony at about eight weeks but are fed by the adults for some time afterwards, even well away from the breeding site. Young birds will beg from their own parents and other adults well into the winter, with diminishing returns.

Fully fledged juveniles are brown, coffee-with-cream colored with fine markings on most feathers. The wings and tail are very slightly darker than the body feathers and relatively unmarked. The bill is black, the legs dull pinkish. Limited molt begins during the fall, and the brown feathers of the back are replaced by gray.

Large gulls, including this species, seem to molt during a large part of the year, so plumage changes signaling a transition from immaturity to maturity occur not only between years but within years. The largest gull species take about four years to reach maturity, and their plumage changes throughout that time.

A typical first-year gull is brown, like the Glaucous-winged described here. By the time it is a year old, certain changes are evident in its plumage. Typically the mantle (= back) has become some shade of gray, and white feathering is increasing on the head and breast. The bill becomes pale (pinkish) at the base. The rest of the body and wings and tail look about the same.

By the second spring (about 20 months old), much more of the head and underparts are white, the bill has more pale color at its base, and gray feathers are appearing in the wing coverts. The wings and tail are still the same shade of brown, although both have been molted once.

By their third spring, Glaucous-winged Gulls look much more like adults. The bill has dark markings restricted to the tip and may be starting to turn yellow. Most of the head and body feathers are white (except for dark streaks and smudges on the head and neck). The wings are largely gray, the primary feathers with slightly darker tips and restricted white spots at the very ends. The tail is white, with or without gray spots toward the ends of the feathers.

One of these birds could easily be mistaken for an adult, but the white primary tips are more restricted, there is often a dusky wash across the upper surface of the wings, and the bill usually has a dark tip or subapical ring. there is much variation in plumage at this age. Some individuals look more like two-year olds, others more like fully adults. A small percentage defy categorization.

When the gull is mature, it has an entirely white body and tail and gray mantle, with slightly darker wingtips with white spots in them. The iris is brown, the bill bright yellow with a red spot on the lower mandible, the feet pink. The circumorbital skin is also pink. In nonbreeding plumage, the head and neck are suffused with dusky markings, and a black smudge appears on the red bill spot.

Back in the 1950s, a small group of these gulls from the Protection Island colony were raised to maturity in captivity by Zella Schultz of Seattle Audubon Society, and the variation within any given year class was surprisingly great. This is presumably because different birds have different hormone levels and apparently molt at slightly different times and/or with different degrees of completeness.

That tremendous variety of gulls that we see out there is caused, at least in part, by the gradual plumage change from young to adult in each species. Learn it in the Glaucous-winged Gull, and you will feel a sense of satisfaction at having made complexity somewhat simpler.

Dennis Paulson