West Side. Nesting pairs occur near most of the large lakes and reservoirs and many large rivers; representative breeding locations include Lake Almanor, Lake Oroville, New Bullards Bar Reservoir (Yuba County), Bass Lake (Madera County), and Lake Isabella, where fairly common. During both spring and fall migrations, they are more widespread and might be observed over any habitat type below the Upper Conifer zone, though rarely far from water.
East Side. Uncommon and scattered; several pairs nest each year on tufa towers at Mono Lake, flying to distant lakes to find fish; they also breed in the Tahoe Basin and other lakes in Mono County; breeding season observations in Alpine and Inyo Counties.
TRENDS AND CONSERVATION STATUS Common until the second half of the 20th century, the introduction of DDT and other chemicals led to a dramatic decline in Osprey populations throughout their North American range. Since DDT was banned in the 1970s, Osprey numbers have steadily increased. The creation of numerous reservoirs and artificial nesting structures facilitated an increase in population and expansion of their range in the Sierra.
HAWKS AND RELATIVES
Family Accipitridae
All species in this large and diverse family are daytime predators with keen eyesight, sharp talons, and hooked beaks for dismembering and devouring prey. Like owls, they often consume whole animals and digest them in their highly acidic stomachs. Fur, feathers, and bones are then passed on to the gizzard (a muscular stomach), compressed into pellets, and regurgitated. These pellets, or castings, provide useful information about diets. Females are larger than males, but most species do not show noticeable plumage differences between the sexes.
Female kites and harriers lay four to six eggs, while most hawks only lay two to four eggs. All Sierra members of this family have buffy-white eggs that are variably splotched with brownish or maroon streaks. Female kites, harriers, and hawks incubate the eggs for 25 to 35 days, with occasional help from the males, who provision food to the females and nestlings. Eagles only lay two eggs, which both parents incubate for 35 to 45 days. All raptors begin incubating their eggs after the first one is laid (unlike waterfowl and many other birds), so they hatch asynchronously and the youngest nestlings may starve or be eaten by their older siblings if food is in short supply. Immatures require at least one and, in some species, two or more years to achieve adult plumage. Golden and Bald Eagles take four or five years, respectively, to reach maturity. Worldwide this family is represented by about 205 living species, and 13 of these occur annually in the Sierra. The family name is derived from L. accipiter, to grasp or seize.
White-tailed Kite
Elanus leucurus
ORIGIN OF NAMES “Kite” may derive from an Indo-European root meaning to shoot or move quickly; elanus, from Gr. elauno, to harass or drive forward; leucurus, from Gr. leukos, white, and oura, tail.
NATURAL HISTORY Attired in bold shades of white, gray, and black, hovering White-tailed Kites grace open landscapes of the Sierra foothills. Some long-term residents call them “Angel Hawks” for this behavior. From hovering positions 20 to 100 feet above fields and pastures, kites scan intently for the movements of meadow voles. Nearly their entire diet consists of these small rodents, making kites an effective regulator of rodent populations. When voles or other prey are spotted, kites have the peculiar habit of making slow, vertical descents by pulling their wings up into a steep “V” and parachuting gently downward feet-first. It’s a surprisingly effective strategy, with capture rates approaching 50 percent. This degree of specialization has its drawbacks, however, for kite populations fluctuate broadly in close synchrony with the ebb and flow of vole populations.
Kites take advantage of peak rodent numbers in late March and April to ensure the best chance of raising their young in the face of a fluctuating food supply. By rearing clutches of four or five eggs, and double-brooding in good years, they end up having one of the highest reproductive success rates of all local hawks. Pairs build nests among the dense outer foliage of trees, exceedingly well concealed from below but open to the sky above so they can scan for approaching danger. Females incubate the eggs for about 30 days while the males provide food for mates and young throughout the entire nesting period, sometimes transferring food to the female in midair exchanges. The young attain flight in about 40 days, but they return to the nest to receive handouts from their parents for up to six months.
STATUS AND DISTRIBUTION Year-round residents that nest below 2,000 feet, White-tailed Kites scarcely make it into the western fringe of the Sierra foothills. They favor wet meadows, grasslands, oak savannas, irrigated pastures, and alfalfa or hay fields, dropping out at elevations where trees start forming a continuous cover. By all accounts, they remain close to water, probably because voles and other prey are most abundant there. They prefer to nest in or near open areas where they can readily hunt. After the breeding season, kites may wander over a wider range, sometimes appearing at higher elevations and on the East Side.
West Side. Uncommon and localized year-round residents below the Lower Conifer zone but casual as high as the Sierra crest, especially in late summer; outside their few known Sierra breeding areas, kites might be seen dispersing high overhead.
East Side. Generally quite rare except for a spate of activity in the mid-1970s, when population numbers were at a high and West Side birds were wandering, probably to avoid a drought when a handful of birds showed up around Reno, Sierra Valley, and Honey Lake in fall with some into winter or were observed in transit elsewhere; other fall and winter records from Honey Lake, Sierra Valley, Mono County, and Owens Valley attest to the ability of this species to disperse widely outside the breeding season; a few spring records from the north end of the Owens Valley are exceptional.
TRENDS AND CONSERVATION STATUS These elegant birds suffered a precipitous decline in the first half of the 20th century at the hands of hunters and egg-fanciers. Fully protected in California in the 1960s, well before the state or federal Endangered Species Acts were passed, kites began a dramatic recovery that lasted well into the 1970s. Their success is a function of their unusually high reproductive rate and ability to tolerate some habitat fragmentation and human disturbance, but their population growth has also been linked to a 40 percent expansion of irrigated agricultural land between 1944 and 1978. Since then, their population may be declining, perhaps as a result of residential and commercial development of former agricultural lands or conversion to more intense agriculture like vineyards and orchards in the Central Valley and Sierra foothills.
Bald Eagle
Haliaeetus leucocephalus
ORIGIN OF NAMES “Bald” for white head color of adults; both Fr. aigle and OE. eagle are derived from L. aquila, eagle; similar to aquilo, the north wind, a symbol of Roman military prowess; haliaeetus, sea eagle, from Gr. hals, sea, and aetos, eagle; leucocephalus, white-headed, from Gr. leukos, white, and kephale, head.
NATURAL HISTORY Bald Eagles are familiar to most people as the country’s national symbol. They are also the second largest bird of prey in North America, after the California Condor, with wingspans exceeding seven feet. They obtain much of their food by scavenging animal carcasses or using their formidable size to steal freshly caught items from other more efficient predators like Ospreys and Great Blue Herons. All types of carrion and prey are consumed, with fish being preferred and forming the bulk of their diet, although they also take many American Coots and waterfowl during the winter. Along Highway 395 in the northeastern Sierra, road-killed deer carcasses are especially preferred and injured waterfowl are pursued in hunting areas in the Central Valley and Sierra foothills. Bald Eagles capture fish and other animals by swooping down from perches or from flight.
For successful nesting, Bald Eagles require sizable bodies of water with dependably productive fisheries, suitable nest sites, and little human disturbance. Recent studies show that younger Bald Eagle pairs are nesting closer to areas of human activity than older pairs, suggesting habituation to human presence. Peak nesting in the Sierra takes place