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The California Condor is one of the most spectacular and highly endangered birds in the world. The largest of the North American vultures, it is also currently the largest soaring land bird of the continent, although it was greatly exceeded in size by a variety of native teratorns of the Pleistocene. Its wingspread of about 2.8 m and body weight of about 8.5 kg make it a near twin in size to the Andean Condor (Vultur gryphus) of South America, and together these two species crown the extant communities of scavenging birds in the New World. Rarely flapping, except during takeoff and landing, condors are superb gliders that cover enormous distances in their daily activities and occupy huge home ranges, consonant with the dispersed and erratic nature of their food supplies.
Earlier known as the California Vulture or Royal Vulture, the California Condor is an exclusive carrion feeder, primarily dependent on large mammalian carcasses, and it enjoyed a wide North American distribution prior to the late Pleistocene megafauna extinctions. Comparable to the Old World griffon vultures (genus Gyps) in many ecological characteristics, the species is highly social in feeding behavior, congregating in substantial numbers at carcasses and bathing sites, and commonly associating in communal roosts, both in nesting and foraging regions. Both condors and griffon vultures also share many physical features, such as feet adapted mainly for walking and a tendency toward unfeathered heads and necks. Both kinds of vultures also feed their young by regurgitation and exhibit nearly equal sharing of nesting duties between males and females. Unlike the griffon vultures, however, condors do not build substantial nests of twigs and branches, and instead rely on natural cavities for reproduction, most commonly caves in cliffs. Perhaps because of the usually dispersed nature of their nest sites, they are not known to have ever nested in the dense colonies typical of many of the griffons, and in this respect condors are more similar to other large solitary-nesting Old World vultures, such as the Lappet-faced Vulture (Torgos tracheliotos).
An invariable clutch size of a single egg and a minimum of 6 years to attain sexual maturity in the wild make the California Condor crucially dependent on low mortality rates to sustain its populations. Its endangerment has evidently been due primarily to excessive mortality, caused in large part by various sorts of poisoning and shooting. Because of the condor’s continuously declining abundance and progressive range contraction, its extinction has been confidently predicted by naturalists almost throughout history.
By 1987, the only California Condors still in existence were captives at the San Diego Wild Animal Park and the Los Angeles Zoo. First breeding of the species in captivity was achieved in 1988; since then, captive production of the species has been substantial. Attempts to reintroduce the species to the wild have been underway in California since 1992 and in Arizona since 1996. These attempts have not yet achieved viable wild populations, in part because of high mortality that can be traced to continuing lead-poisoning threats in the wild.
This condor has received intensive study since the late 1930s. Principal historical research on its natural history and conservation was conducted by Robinson ( 1939, 1940), Koford ( 1953), Miller et al. ( 1965), Sibley ( 1968, 1969, unpubl.), and Wilbur ( 1978b), although it has also been the subject of dozens of additional specialized studies and popular accounts. An intensive program of the 1980s, involving numerous organizations, led to a detailed characteriza-tion of many aspects of its biology, with special emphasis on determination of limiting factors (Snyder and Snyder 1989, 2000). Despite the difficulties in studying such a wide-ranging species, the primary environmental constraints it has faced, especially various mortality factors, are now relatively well known.