Western Grebe
Aechmophorus occidentalis
ORIGIN OF NAMES Aechmophorus from Gr. aichme, spear, and phoreus, bearer; L. occidentalis, western.
NATURAL HISTORY These largest of North American grebes (along with Clark’s Grebe, see account below) are also the most widespread grebes in the Sierra. Scanning across an expanse of open water, birders often spot these large diving birds as specks of white bobbing in the distance. A closer look reveals the bright white breasts and long, snake-like necks of Western Grebes. They may appear headless, because they often sleep with heads and necks drawn back with bills pointing forward. They feed by diving and pursuing their prey under water, and they usually forage in water at least four feet deep. Westerns (and Clark’s) have a neck mechanism, unique among grebes, that permits them to thrust their heads forward like spears (a fact painfully learned by one of the authors when rescuing a grebe tangled in fishing tackle). A similar mechanism has been well described for herons but has not been studied in grebes. Westerns consume more fish than most other grebes, but they also eat mollusks, crustaceans, insects, and rarely amphibians and aquatic plants. They dive to avoid predators and can remain submerged for up to a minute.
In the breeding season, Western Grebes require a large extent of open water for feeding and resting, a good supply of fish, and cattails, tules, or flooded riparian trees for securing their floating nests. Pairs of Western Grebes perform elaborate courtship displays, swimming side by side then running rapidly with their bodies erect, heads and bills pointed skyward, and only their feet touching water. In the Sierra, courtship mainly occurs from April to May, and nests can be occupied from May until August; fall nesting has been documented at Lake Isabella, with downy young riding on their parents’ backs. They are monogamous breeders, nesting in dense colonies that may contain hundreds of closely spaced nests. Nests are composed of decaying aquatic plants and some green plants mounded on mud or submerged plant root masses in shallow water. They also construct floating platforms of dead plant material and anchor these to emergent plants. Parents take turns incubating the eggs, and pairs will renest if their nests are lost to predators. The precocial young leave their nests at hatching and ride on the backs of both parents. Young can swim and feed themselves soon after hatching, but their parents still feed them for four or five weeks, until they are nearly full-grown.
STATUS AND DISTRIBUTION Outside the breeding season, Western Grebes are often found in significant numbers on most large lakes and reservoirs.
West Side. Common nesters at Lake Almanor in the north and at Lake Success and Lake Isabella in the south but apparently do not breed elsewhere on the West Side; fairly common nonbreeding visitors to nearly all large foothill reservoirs; rare visitors to large Subalpine and Alpine lakes in summer and fall, especially if fish are present.
East Side. Common from April through November at Boca Reservoir, Prosser Creek Reservoir, Lake Tahoe, Topaz Lake, June Lake, Bridgeport Reservoir, and Crowley Lake; common nesters at the latter two reservoirs; casual to rare in winter.
TRENDS AND CONSERVATION STATUS Western Grebes, like all colonial water birds, are vulnerable to development around lakes and reservoirs and to other human disturbance near their nesting colonies. Personal watercraft and motor boats have been observed near breeding colonies in flooded riparian forests at Lake Isabella and could be a serious disturbance factor there and at other Sierra nesting locations. Drawdown of water for hydroelectric generation during the breeding season has marooned nests in the past at Lake Almanor. Several thousand Western and Clark’s Grebes died at Lake Isabella in August and September 2005; the suspected cause was a bacteria bloom that produced neurotoxin that poisoned fish and secondarily poisoned grebes as well as other water birds such as herons and ducks. A similar die-off occurred at Lake Success in 2006, and mortality probably occurs at lower levels at these and other reservoirs in most years.
Clark’s Grebe
Aechmophorus clarkii
ORIGIN OF NAMES “Clark’s” for J. H. Clark (1830–?) a surveyor and naturalist who collected the first specimen of this species (not the Clark of the Lewis and Clark Expedition, see Clark’s Nutcracker account).
NATURAL HISTORY First described in 1858, Clark’s Grebes were not considered a full species by the American Ornithologists’ Union until 1985. Previously they were classified as a subspecies of the more common and similar-appearing Western Grebe. The breeding and wintering distribution of these two species overlap throughout their ranges in western North America, and they often flock together throughout the year, even during the breeding season when the two species may nest in mixed colonies.
STATUS AND DISTRIBUTION Little is known about the historical status and distribution of this species because most sightings before 1985 were recorded as “Western Grebes.” Clark’s typically occur in smaller numbers than Western Grebes in the Sierra and elsewhere in California.
West Side. Uncommon migrants and winter residents at foothill reservoirs; similar to Westerns, they breed only at Lake Isabella in the south and at Lake Almanor in the north.
East Side. Fairly common breeders at many of the same lakes and reservoirs as Westerns; uncommon in winter.
TRENDS AND CONSERVATION STATUS See Western Grebe account, above.
CORMORANTS
Family Phalacrocoracidae
Cormorants must leave the water periodically to dry in the sun because their feathers are not fully waterproofed like a duck’s. The structure of cormorant feathers decreases their buoyancy and eases their underwater pursuit of fish. Six of the world’s approximately 30 cormorant species occur in North America. Three species—Brandt’s, Pelagic, and Double-crested Cormorants—occur commonly at bays and protected estuaries of the California coast, but only the Double-crested regularly ventures inland. The family name is derived from Gr. phalakros, bald, and korax, a raven.
Double-crested Cormorant
Phalacrocorax auritus
ORIGIN OF NAMES “Cormorant,” a sea crow, from OF. cormaran; phalacrocorax ( see family account above); L. auritus, eared, for the long, upturned feathers (crests) on their heads that are worn for only a short time during the breeding season.
NATURAL HISTORY With wet wings spread, Double-crested Cormorants perch like awkward black gargoyles on snags or branches of riparian trees. When they swim, their heads and bills are typically cocked upward. Cormorants frequent large bodies of water that provide ample room for their labored takeoffs and small fish, their favored prey. Diving from the water’s surface, they may pursue fish to depths of 5 to 25 feet and can stay submerged for up to 30 seconds. They are equally at home on salt and fresh water, as long as fish are plentiful.
Double-crested Cormorants are colonial breeders that nest on islands or in large trees along lakes and large rivers, often in association with Great Blue Herons, Great Egrets, and other colonial species. In the breeding season, mated cormorants display to each other by stretching up their heads and necks, showing off bright orange throat patches and turquoise blue mouth linings. Both members of the pair participate in building their large nests, up to two feet in diameter and composed of twigs, sticks, and other debris placed in large trees. Nesting in the Sierra generally extends from April until late July. Females usually lay three to four pale blue eggs, and both adults incubate them for about 28 days until hatching. Adults feed and fend for their young until they are independent at about 10 weeks. During the nestling and fledgling period, both adults provide their young with regurgitated fish, crustaceans, frogs, or aquatic insects.
STATUS