Perilously close to extinction in the lower 48 states three decades ago, the bald eagle has made a remarkable comeback, owing to restrictions on contaminants, enforcement of protective laws, and special management programs designed to improve its reproductive success and survival.
The bald eagle (Haliaeetus leucocephalus), our national symbol and one of North America's largest birds, weighs about 8 to 14 pounds and has a wingspan of 6½ to 8 feet. Females are larger than males, and birds of northern states and provinces tend to be larger than those from the southern portions of the breeding range. Adults are dark brown with a pure white head and tail. Younger birds are mostly brown, mottled with varying amounts of white. They acquire their adult plumage at 4 or 5 years of age.
The range of this raptor is wholly within North America, including Alaska, Canada, the lower 48 states, and northwest Mexico. Bald eagles in winter may be found throughout most of California at lakes, reservoirs, rivers, and some rangelands and coastal wetlands. The State's breeding habitats are mainly in mountain and foothill forests and woodlands near reservoirs, lakes, and rivers. Most breeding territories are in northern California, but the eagles also nest in scattered locations in the central and southern Sierra Nevada mountains and foothills, in several locations from the central coast range to inland southern California, and on Santa Catalina Island.
Some individuals may live for decades in the wild. A breeding pair may remain together until the death of one member, and the surviving bird may soon find a new mate.
Normally, the eagles build their large stick nests in the upper canopy of the tallest trees in the area. The adults may repair the same nest annually, increasing its size over time, or they may build a new nest in their territory or repair one they had used formerly. In many cases, the territory of a pair of eagles may include several nests in addition to the one they most recently used.
In most of California, the breeding season lasts from about January through July or August. One or two eggs (occasionally three) are laid in late winter or early spring, and incubation lasts about 35 days. Chicks fledge when they are 11 or 12 weeks old. In a matter of weeks after leaving the nest, many of the still naive young birds suddenly strike out on their own and rapidly migrate hundreds of miles to the north. In these post-nesting dispersal areas, the young birds join other bald eagles to feed on salmon and other plentiful food. Telemetry studies show that some of these young birds reach northern and western Canada before returning to California a few months later. California's resident breeding pairs remain in California during winter, typically in the vicinity their nesting areas, except when winter conditions are too severe and they must move to lower elevations.
Hundreds of migratory bald eagles from nesting areas in northwestern states and provinces spend the winter in California, arriving during fall and early winter. These wintering birds may remain until February or March, or even into April. In late winter, some adult bald eagles in California have already started nesting, while other eagles have not yet returned to their more nesting territories north or northeast. Some of the adults that winter here have been tracked to their nesting territories in north-central Canada 2,000 miles away.
Bald eagles prey on a variety of small animals, usually fish or waterfowl, and they eat carrion, including salmon, deer, and cattle.
History and Problems
Historically, bald eagles were widespread and abundant in California, but no historical information exists on population size. By the late 1960s and early 1970s, when the bald eagle was listed as an endangered species, fewer than 30 nesting pairs remained in California--all in the northern third of the State. Contaminants across the landscape posed a serious problem for bald eagles. Shortly after World War II, DDT pesticide was used extensively to control mosquitoes and other insects. It was later determined that DDT and its residues were poisoning bald eagles causing egg shell thinning that resulting in many failed nesting attempts. DDT also affected other species such as peregrine falcons and brown pelicans. DDT was banned in the United States in 1972 due to it's negative effects on wildlife species. Another contaminant causing bald eagles deaths is lead. Lead has and is still poisoning bald eagles throughout the United States when eagles inadvertently feed on contaminated prey or carcasses.
The bald eagle was added to the Federal list of endangered species(opens in new tab) in 1967, and to the California list of endangered species (PDF)(opens in new tab) in 1971. The Fish and Wildlife Service removed the bald eagle from the list of threatened and endangered species in August 8, 2007, but remains endangered in California. Although the Fish and Wildlife Service removed the bald eagle from endangered status, the bird will still be protected by the Migratory Bird Treaty Act(opens in new tab) and the Bald and Golden Eagle Protection Act(opens in new tab). Both laws prohibit killing, selling or otherwise harming eagles, their nests, or eggs. The Fish and Wildlife Service has recently revised a final rule on two new permit regulations that would allow for the take of eagles and eagle nests under the Bald and Golden Eagle Protection Act (Eagle Act). Also, the bald eagle is classified as a "fully protected bird (PDF)(opens in new tab)" under California law.
The most significant threat to survival of the bald eagle in the 20th century was the widespread use of the pesticide DDT in the decades after World War II, which caused abnormalities in bald eagle eggshells, resulting in widespread nesting failures. Other adverse impacts have included habitat modification from road, housing, and other developments; agriculture; timber harvest; pesticides and contaminants, including lead poisoning; off-road vehicles and other human disturbances; electrocution and collision at power lines; and shooting.
A nationwide ban on most uses of DDT took effect in 1972, and over time, this enabled bald eagle reproduction rates to return to satisfactory levels. However, nesting failures from this source still occur in some areas in California and elsewhere nationally. Local protection of nesting pairs from adverse habitat changes and disturbances, restrictions on the use of lead shot, enforcement of laws prohibiting killing eagles, and other protective measures benefitted the eagles, as well. Populations have been able to thrive and reproduce adequately in most of California. Bald eagles have been able to re-occupy much of their former range.
Many breeding territories are being maintained and protected under local management plans. Key winter habitats are monitored annually. Public land agencies-such as the U.S. Forest Service and county and State parks-provide site protection and public viewing and education opportunities. California Department of Fish and Wildlife protects bald eagle nesting, foraging and wintering habitats in various parts of the State on its Ecological Reserves and Wildlife Areas.
Cooperating agencies and individuals monitor the breeding status of nesting territories in the State. The Department maintains a database on the annual status of all known territories. Data are submitted annually by various partners using the California Bald Eagle Nesting Territory Survey Form (PDF Form). California participates, also, in the Midwinter Bald Eagle Survey. This annual, nationwide survey is carried out by volunteers and agencies in wintering areas to sample population size and distribution of wintering birds. State and federal agencies and other entities have sponsored biological studies, including intensive ecological investigations undertaken by Pacific Gas and Electric Company, U.S. Forest Service and the Santa Cruz Predatory Bird Research Group.
Since 1980, dozens of birds were translocated to Santa Catalina Island as chicks or eggs from wild nests on the mainland or from captive breeding (Institute for Wildlife Studies). In a second reintroduction effort, 66 eaglets were translocated and released from 1987 to 1995 in the central coast mountains south of Monterey Bay (Ventana Wildlife Society). The first nesting pair from those releases formed in 1993, and many more pairs have established territories in the central coast range counties since then. From 1985 to 2007 the San Francisco Zoo, at its Avian Conservation Center operated captive breeding efforts for bald eagles, hatching and releasing 103 eagle chicks on the Channel Islands of California.
The Pacific Bald Eagle Recovery Plan, adopted by U.S. Fish and Wildlife Service in 1986, encompasses a seven-state area that includes California. California Department of Fish and Wildlife participated on the Recovery Team that prepared the plan. The following recovery goals were established to guide and measure population recovery: 1) a minimum of 800 breeding pairs, 2) average annual productivity of at least 1 young per active breeding pair, 3) breeding population goals met for at least 80% of management zones, and 4) no decline in major winter concentrations.
Protection of nesting areas, restrictions on use of DDT, and other special wildlife management actions have allowed the population to rebound. The number of breeding pairs in the Pacific states is approaching twice the minimum goal listed in the recovery plan, and progress in meeting the other criteria has been good. The status of the species has generally improved, as well, in the rest of the lower 48 states.
Today bald eagle populations have rebounded across the United States. Numbers in California are on the rise, but population estimates are lacking. Continued monitoring is essential to determine the trend for bald eagles.
Population Status and Trend
The number of breeding pairs known to be occupying territories in California is steadily growing. Along with this growth, the breeding range is expanding in California (range map (PDF)(opens in new tab)). In 1977, bald eagles were reported to be nesting in eight counties, and by the mid-1990's, bald eagles were found nesting in 28 of the State's 58 counties. Today, bald eagles are found 41 of the State's 58 counties. Reintroduction programs have fostered the establishment of breeding pairs in several of those counties.
The annual, nationwide Midwinter Bald Eagle Survey indicates that the State's winter population appears to be at least stable, although varying from year to year, exceeding 1,000 birds some winters. The results of Midwinter Bald Eagle Surveys conducted from 1986-2005 estimates a 1.2% increase in California's wintering bald eagle population. Typically, about half of the State's wintering bald eagles are found in the Klamath Basin along the California-Oregon border, the location of the largest winter concentration of Bald Eagles in the lower 48 states.
The future looks bright for the bald eagle in California and in the nation. The growing population of eagles allows more people to see them. The best time see to bald eagles is in the winter, between December and March, when large numbers of migratory and resident eagles congregate at favored feeding areas. Some recreational areas offer eagle viewing tours.