Amazing grebes are perfectly suited to life on and under the water
Published: December 22, 2011
|The waterbirds known as grebes are more adapted to an aquatic lifestyle than any other group. They don’t have to go on land at all. Courtship, copulation, and feeding take place on or in the water. They even build floating nests and brood youngsters on their backs.|
Grebes’ lower legs and feet are perfectly suited to the water. They are strongly compressed laterally to minimize drag while swimming and diving. The toes are flattened and have stiff, flat lobes. Even the “claws” are flattened; they resemble human fingernails.
The lobes project to the side when the birds make their power stroke while paddling but do not fold back during the recovery stroke, as they do on other birds that have lobed toes. Instead, grebes rotate their toes before they bring the foot forward, so the lobes knife smoothly through the water.
The position of grebes’ legs is unusual, too. Displaced far to the rear and to the sides, they project out, rather than down, while grebes swim. The action no doubt explains the origin of the name Podiceps, the genus of Horned, Red-necked, and Eared Grebes. It means “bumfoot.”
Grebes have more feathers than most other birds. The feathers are densely arranged on the abdominal, or ventral, parts of their bodies, and the number and size of regions without feathers are reduced. The dense mat of feathers, called “grebe fur,” was used to make clothing many years ago.
The barbs near the tips of the ventral feathers lack hooks, so they do not form rigid webs but become twisted in coil-like patterns (contributing to the “fur”). The coils absorb and hold water, which probably increases the bird’s specific gravity for diving and smoothes the feather surfaces to prevent turbulent flow. The surface tension of the water in the coils may also provide a skin-like barrier that prevents water from penetrating to the bird’s actual skin.
While feather density is high in areas in contact with water, it is lower on the rear parts of the bird. Grebes can raise their tail and rump feathers, allowing sunlight to reach the black-pigmented skin underneath, which functions as a heat-gaining mechanism.
Grebes of North America
Almost two dozen species of grebe exist worldwide. The following seven are found in North America.
Least Grebe Tachybaptus dominicus
Pied-billed Grebe Podilymbus podiceps
Horned Grebe Podiceps auritus
Red-necked Grebe Podiceps grisegena
Eared Grebe Podiceps nigricollis
Western Grebe Aechmophorus occidentalis
Clark’s Grebe Aechmophorus clarkii
Equally unusual is that adult grebes swallow feathers and feed them to their young. The feathers break down in the stomach to a felt-like mass that blocks the opening to the small intestine, thereby preventing fish bones, the outer coverings of beetles, and other hard materials from entering the intestine. The birds regurgitate the indigestible material as a pellet.
Studies have shown that the feathers ingested by grebes are almost all grebe feathers. So how do the birds get them? Observations reveal that grebes often pluck feathers from their own flanks, areas that appear to be in constant molt — thereby maintaining a continuously feathered area.
Grebes can be pugnacious, especially during pair formation. Paired birds often attack unpaired birds that come too close while advertising for mates. Grebes usually attack other birds with their necks outstretched and their narrow, pointed bills held like a spear. The birds swim rapidly toward the intruder or run on the water while flapping their wings. Sometimes they fly toward a rival, dive before reaching it, and then come up to spear it from below. Horned Grebes have used this technique to drive away flocks of much larger Graylag Geese.
The spectacular courtship displays of grebes are among the most complex of all birds. They involve both sexes and are usually performed in open water. During many of the displays, males and females assume the same posture, but with some, the postures are different. In most birds, when postures differ, males display one, females the other. But in grebes, either sex can assume either posture. Almost unbelievably, this also includes copulation. Sometimes a female will mount a male — although there is no evidence that such mountings are successful.
In general, courtship begins when a single grebe calls and another bird responds with a call. The grebes then swim toward each other and dive and surface with wild body displays and more diving. The displays build as the birds move close together. Finally, there is a flurry of activity. Some grebes rise out of the water and bump chests, while others paddle rapidly on the surface, actually coming out of the water.
The displays of Great Crested, Western, and Clark’s Grebes are most extreme. (Great Crested is found across Europe and Asia.) Holding their necks and heads erect or curved back and then forward like question marks, the birds run side by side atop the water. (Scientists call the display a rush or penguin dance.) Courtship ends with weed sharing — in some species, a simple transfer, in others, an elaborate extension of the rush.
The fascinating anatomy and behavior of grebes makes them among the most amazing birds.
Eldon Greij is professor emeritus of biology at Hope College, located in Holland, Michigan, and the founding editor of Birder's World (now BirdWatching) magazine.
Read more by Eldon Greij.