Aechmophorus
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Aechmophorus is a genus of birds in the grebe family.
It has two representatives breeding in western North America.
- Western Grebe, Aechmophorus occidentalis
- Clark's Grebe, Aechmophorus clarkii
Contents
Introduction
Genus Aechmophorus The Western Grebe and the Clark’s Grebe are classified in Order Podicipediformes, Family Podicipediae, Genus Aechmophorus and Species Aechmophorus occidentalis and Aechmophorus clarkii respectively. Although the two species look very similar, bill shape and coloration, as well as feathering around the scarlet eye of the bird can be used to determine the precise species.Distinguishing Features
The Western grebe has a straight bill with a dull green-yellow color as opposed to the Clark’s grebe, which has a slightly upturned, bright orange-yellow bill. In both species the male has a longer and deeper bill than that of the female, making it a distinguishing feature (6). All species of grebes display the pattern of lobed feet. A tough skin surrounds each toe separately, providing more surface area for effective swimming. This form increases the power of propulsion per stroke and reduces drag when the bird is recovering (1). Skeletal measurements taken from both species, when averaged together, revealed that for the most part the Western grebe is larger than the Clark’s grebe (3). The two species also differ in their advertising calls. The Western grebe gives a call that includes two distinct “cree-cree” notes, while the Clark’s grebe consists of a single “creeet” note, more drawn out (4).Diet and Foraging
These two species, like most grebes, eat a diet consisting mostly of fish. They are also known to forage on crustaceans, insects, worms and salamanders (2). Foraging techniques are composed of a number of foot-propelled dives. Current research is associating the use of springing dives by the Clark’s grebe, in which the bird essentially leaps from the water before submerging, which allows the bird to reach deeper below the surface, with possibly proving niche separation between the two species (6).Habitat, Migration and Nest Site
Western North America is home for nearly all individuals of both species of grebes. When migration occurs, the birds in the northern range will travel west in flocks, at night to the pacific coast. Both Western grebes and Clark’s grebes winter in sheltered bays or estuaries on the pacific coast and summer in freshwater lakes with marshy vegetation as well as large open areas of water. The site of nesting is usually in a shallow water marsh. Both males and females help to build a floating platform nest of vegetation (2). Because of the colonial nature of these birds nests must be continually guarded during the breeding season. If left unattended other pairs of birds seeking nest sites will seize the platform (7).Mating Systems
Western grebes and Clark’s grebes take part in a courtship display known as mate feeding. This occurs regularly between a mated pair during the period prior to hatching of nestlings. In both species mate feeding appears to peak shortly before egg laying and involves the male providing large quantities of food to the begging female (7). Two males will also compete for a female’s attention, in a spectacular display, by rearing up and rushing across the surface of the water side by side, making a loud pattering sound with their feet (2).Nestlings and Fledging
The typical clutch size for both Western and Clark’s grebes is between 2 and 4 eggs per season. They are usually a pale bluish white and become stained by the nest to a speckled brown (2,7). Downy young of the Western grebe display a uniform gray along the back, a white belly along with a dark patch on the forehead. This differs in Clark’s grebes where the young are almost entirely white. Both species of nestlings have an area of skin on the crown that changes color from orange to scarlet if the chick needs feeding or is in distress (8). Males tend to hunt and provide chicks with food more often than females, however only one fish can be caught during each dive (3). Fledging occurs just hours after the last nestling emerges from its shell. The semialtricial nestlings travel on the backs of their parents for several weeks, this is referred to as back brooding and both parents participate in the activity. For the first two weeks after hatching chicks are completely camouflaged by their parents back feathers and will progressively become more visible. Chicks will stay close to their parents when predators are spotted or during feedings (5).Work Cited
1. Johansson, L. C., Norberg U. (2001) Lift-Based Paddling in Diving Grebe, The Journal of Experimetal Biology 204, 1687-1696.2. Kaufman, K. (1996) Lives of North American Birds. New York, NY Houghton Mifflin Company, 11-12.
3. Livezey, B., Storer, R. (1992) Morphometric Comparison of Skeletons of the Western Grebe Complex Aechmophorus of the United States and Canada, The Condor 94, 668-679.
4. Nuechterlein, G. (1981) Courtship Behavior and Reproductive Isolation Between Western Grebe Color Morphs, The Auk 98, 335-349.
5. Nuechterlein, G. (1988) Parent-Young Vocal Communication in Western Grebes, The Condor 90, 632-636.
6. Nuechterlein, G., Buitron, D. (1989) Diving Differences between Western and Clark’s Grebes, Auk 106, 467-470.
7. Nuechterlein, G., Storer, R. (1989) Mate Feeding by Western and Clark’s Grebes, The Condor 91, 37-42.
8. Storer, R. (1967) The Patterns of Downy Grebes, The Condor 69, 469-478.
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