Sexual attitudes at Northern latitudes

Natural History, July-August, 1998 by Richard B. Lanctot

When buff-breasted sandpipers reach the Tundra, the mating Games begin.

Spreading his wings to reveal their pearly white undersides, the male buff-breasted sandpiper tilted his head to the sky, puffed out his chest, and uttered a series of soft "tick-ticks." He then proceeded to stamp his feet and vibrate his wings as if the ground were quaking beneath him. Soon, three females, attracted by this courtship display, entered the curve of his embracing wings. They then spread their own wings and turned so their backs were against his chest, each jostling for the position closest to him. Just when mating seemed inevitable, a neighboring male rushed into the group, forcing all the birds into the air.

Such scenes are common among buff-breasted sandpipers on their Arctic breeding grounds. Migrating alone or in small flocks, the birds leave their wintering grounds on the pampas of Argentina in mid-January to early March. After passing over the Gulf of Mexico and the plains of North America, they arrive on the Arctic coast in late May or early June. For three summers, I studied these birds and their varied mating rituals on the tundra of northern Alaska.

Flashes of the white underwings of displaying males are visible from half a mile away and are the first sign that these otherwise well-camouflaged and unobtrusive shorebirds have arrived on the vast Arctic tundra. Males first begin to display on snow-free areas, usually the dry, elevated slopes parallel to the many waterways draining into the Arctic Ocean. As the brief breeding season progresses and more snow melts, they display throughout the tundra in groups of up to twenty males--congregations known as leks. (Lekking species include other birds, such as greater prairie-chickens and violet-headed hummingbirds, as well as mammals, including European red deer and hammerheaded bats; and numerous species offish and insects.) Within the lek, male buff-breasted sandpipers defend, and try to lure females to, individual territories that range in size from fifty square yards to two acres. Territories offer females no resources, such as food or nesting places, but serve simply as a spot on which to mate. To catch the eyes of females passing overhead (sometimes at heights of more than 1,000 feet), a male buff-breasted sandpiper lifts and waves one or both wings and periodically raises his tail, jumps up and down, and flies short circuits around his territory. Few birds can match the sheer variety of buff-breasted sandpiper performances.

In contrast to sites used by most lekking birds, only about 10 percent of buff-breasted sandpiper sites are used year after year; most leks pop up in new locations and may last only a day or two before the males regroup elsewhere on the tundra. The more traditional sites, usually at river junctions, may be strategically located to intercept migrating females. Most buff-breasted sandpipers display for only a few hours to a few days before departing to display at new locations as more snow melts. Other males, called residents, maintain their territories for a week or more before moving on. A few males display alone or near new nest sites--mere scrapes on the sedgy ground made by females in preparation for egg laying.

Establishing a territory on a lek is no small feat. New arrivals are fiercely rebuffed by the ensconced males; chased from territory to territory, most resort to displaying along the outer edge of the lek or even farther afield. To reinforce territory boundaries, neighboring males engage in both ground and aerial contests. When they take to the air, they flutter straight up in tandem, legs dangling, and can reach heights of thirty or more feet before alighting back in their respective territories. Biologists and birders are often alerted to the presence of a lek by the sight of aerial combatants silhouetted against the blue Arctic sky.

Why males display together on relatively tiny, hotly contested sites within the vast open space of the tundra is open to debate. One school of thought, developed from studies of other lekking species, holds that females find it easier to locate such congregations than to locate solitary males; that mating at a lek minimizes disturbance at nest sites; and that once on a lek, females can compare males and select the best-quality mate. Another school focuses on the male's perspective: in groups, males may be safer from predators (in the case of buff-breasted sandpipers, these include Arctic foxes and peregrine falcons). Leks may also form as males display at "hot spots" frequently visited by females, or as less attractive individuals take advantage of the drawing power of a superior male (known as a "hot shot") by clustering around him.

On any given buff-breasted sandpiper lek, only a few males succeed in attracting and courting the majority of the females that visit. Males routinely fly into territories of neighbors that have attracted females, disrupt their courtship, and try to lure the females away. Others are more surreptitious; they resort to sneaking into adjacent territories. Alternately crouching and creeping, they approach within a few feet of the resident male's display site and wait until the resident has attracted one or more females. Because male and female buff-breasted sandpipers look alike--apparently even to one another--these sneaky males can then join the female entourage and participate in the courtship that is a prelude to copulation. At this point, intruders typically disrupt the courtship and try to lure females to their own territories. More rarely, they position themselves between the territorial male and the closest female and attempt to "steal" a copulation. Almost half of all female visits to a lek are disrupted, and more than a third of these disruptions result in the female's leaving one of the males' territories. This may happen time and again, with the female moving from male to male and often not completing a copulation with any of them.