News & Politics » Field & Street

Field & Street

by

comment

I am getting mildly obsessive about finding a cedar waxwing nest. I think there is at least one pair nesting at Somme Woods, the forest preserve where I am doing a survey of nesting birds. There may be several, but I haven't been able to get close to pinning down even the approximate location of any nests.

The birds keep teasing me. Once I saw a pair together in the crown of an isolated tree doing what could have been a courtship ritual. One would fly from one branch to another. The second bird would follow the first and land next to it. They would sit side by side for a moment and then repeat the performance. With cedar waxwings you can't tell males from females by appearance, so I don't know who was following whom. For that matter, I don't know that they were different sexes. Whatever they were they flew off after a bit, and I never saw them again.

Bev Hansen and Bill Valentine, who are also working on the nesting survey, saw a pair passing a berry back and forth. Mutual feeding is a common act of courtship among cedar waxwings. But sometimes the birds perform mutual feeding in groups. Many observers report seeing six or eight waxwings perched side by side on a branch passing a berry from beak to beak from one end of the line to the other and then back, repeating the ritual several times. In fact every action that has been reported as part of the courtship of cedar waxwings is also used by the birds to reinforce the bonds that keep the flock together.

On a few occasions I have seen a single bird hawking for insects from the top branches of a tall dead tree. Hawking, also called flycatching, is a style of hunting. The bird sits quietly on an exposed perch until it sees a likely insect flying by, then it makes a quick sally, snatches the bug from the air, and returns to its perch. Most of my sightings have been of flocks, 10 or 12 birds flying together, just as they do in the winter.

I only half believe that cedar waxwings build nests anyway. They are such elegant birds that it is hard to imagine them engaged in the grubbier aspects of child rearing. It's like visualizing Fred Astaire changing a diaper or poking spoonfuls of oatmeal into a six-month-old baby. A waxwing's plumage is delicate and understated: soft browns fade to yellow on the belly. A simple yellow band adorns the tip of the tail. The bright red tips on the secondary feathers of the wing provide a splash of color--imagine Astaire with a red carnation on the lapel of his tailcoat. The waxwing's crest and the black mask over its eyes add a slightly rakish air to its appearance.

The behavior of waxwings supports their elegant image. They never make a scene in public. They don't fight with each other. They don't scream at each other. Their voices are a soft murmur, and they live practically their whole lives in peaceful, nomadic groups. Often they nest in groups, forming loose colonies of up to 20 pairs.

Even when a pair splits off from the flock to nest alone, the males do not announce the creation of a territory by singing or driving off rivals. In fact, the only territory they defend is the nest itself.

They are also not bound to a particular nesting season. In general they prefer late summer, but they will sometimes nest early in the season, and they have been discovered sitting on eggs as late as mid-September. So it may be that the birds at Somme have already finished nesting for this year, or it may be that they haven't started yet. It's hard to say.

Cedar waxwings belong to a family called the Bombycillidae, a name that means something like "silky plumage." There are only three species in the family. The cedar waxwing is strictly New World, with a breeding range that extends from the northern forest limits in Alaska and Canada to California, Utah, southern Illinois, and, in the mountains, northern Georgia. It withdraws from the northern part of its range in winter to become common along the gulf coast. Occasionally some birds get as far south as Panama.

The Japanese waxwing is exclusively Old World, nesting in the forests of Siberia and China, and wintering in Japan, Taiwan, and Korea, among other places.

The Bohemian waxwing is a circumpolar species that nests in the northern forests of both hemispheres. There is some uncertainty about the source of its common name. It does indeed nest in the forests of Bohemia, but the name may refer to its nomadic habits and lack of a fixed abode.

The closest relatives of the waxwings are the silky flycatchers, a group of four species that live in Central America. Only one species, the phainopepla, reaches the southwestern U.S. Like the waxwings, silky flycatchers have soft, almost velvety plumage and prominent crests. They are also quite social, and they live on a diet of fruit and insects. The little fossil evidence available suggests northern Mexico as the point of origin for both groups.

Both the nomadism and the extreme sociability of waxwings have been shaped by their eating habits and their environment. While they do hawk for insects, about 70 percent of their annual diet is fruit, and wild fruits are not always available. A typical wild cherry tree or mountain ash will produce an abundant crop in one year and little or nothing the following year. So fruit-eating birds have to move around in search of trees that are having a good year. Traveling in flocks makes sense both as protection against predators and as a way to supply extra eyes to hunt for good trees. If the flock finds some good trees, there will be plenty of food for everybody. Most birds that eat insects or other foods that tend to be spread more or less evenly through the environment use territoriality to spread their own populations.

In tropical forests--where a square mile of woods typically holds hundreds of species of trees, shrubs, and vines--fruit eaters can be sedentary. The plants produce fruit throughout the year, and if one species has a bad year, others are available to compensate for the loss.

Northern forests have far fewer species, so fruit-eating birds often have to travel long distances in search of a meal, hence the nomadic habit. Northern seedeaters, notably the crossbills, use a similar strategy. Crossbills feed on conifer seeds that they extract from cones with their unique beaks, and they travel constantly in search of good seed crops. Like the waxwings, they nest when and where food is available, regardless of season. Crossbills are even known to nest in the middle of northern winters if there is enough food around to support them and their young.

Many of these northern species, including the waxwings, are irruptive. Some winters they show up south of their usual homes in large numbers. Other years, they don't show up at all. After long controversies about the reasons for irruptive behavior, there seems to be general agreement that food is the cause. In years without seeds or fruits, northern birds come south looking for something to eat.

The elusiveness of the cedar waxwings at Somme Woods seems to be typical behavior, but then we don't even know how an adult pair divides the task of incubating the eggs. In some species the females do all the incubating. In others the males handle the job alone. Most divide the labor, and the precise nature of the divisions varies enormously. Apparently nobody has ever collected this basic piece of life history for the cedar waxwing.

We do know that both parents feed the young, that they start them out on nutritious, high-protein insects, and that they only switch to fruit after the nestlings have gotten a good start on their growth. Wild fruits are not very nutritious, and waxwings have to eat a lot to get enough calories to keep going. The fruit goes through their short intestinal tract very fast. We don't know whether males or females incubate the eggs, but we do know that a cherry passes all the way through an adult cedar waxwing in just 20 minutes, and it only takes 28 minutes for a blueberry to make its way from beak to cloaca.

Waxwings get their name from the teardrop-shaped extensions on the secondary feathers of their wings. These bright red extensions look and feel like sealing wax. Nobody knows exactly what they do for the birds, but there is some reason to believe they play a role in mate selection. Second-year birds, that is birds born the previous summer, have little or no wax on their wing tips. They don't fully develop this trait until their third year. Older birds have a higher rate of nesting success and seem to seek each other out as mates. The bright red waxy wing tips may be a signal of maturity.

Add a comment