One of the most spectacular and highly endangered birds in the world, the California Condor is the largest of the North American vultures and 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 considered 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 in cliffs and large trees for reproduction. 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 for a juvenile condor 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 this condor's continuously declining abundance and progressive range contraction, its extinction has been confidently predicted by naturalists almost throughout history.
The documentation that condor mortality rates were excessively high, primarily owing to lead poisoning, was the main reason for capture of the last few wild birds to become part of the captive flock in the mid-1980s. By 1987, the only California Condors still in existence were captives at the San Diego Wild Animal Park (now known as San Diego Zoo Global) and the Los Angeles Zoo. First breeding of the species in captivity was achieved in 1988; since then, captive production has been substantial. Attempts to reintroduce the species to the wild have been underway in California since 1992, in Arizona since 1996, and in Baja, Mexico since 2002. Although condors have successfully reproduced at all release sites except Baja, these attempts have not yet achieved self-sustaining wild populations, in large part because of high mortality that can be traced to continued lead-poisoning 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 ( Robinson 1939 , Robinson 1940 ), Koford ( Koford 1953 ), Miller et al. ( Miller et al. 1965 ), Sibley ( Sibley 1968 , Sibley 1969 , unpubl.), and Wilbur ( 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 characterization of many aspects of its biology, with special emphasis on determination of limiting factors (Snyder and Snyder Snyder and Snyder 1989 , Snyder and Snyder 2000 ). Research continues on reintroduced populations, with the knowledge that the intensive management to protect this critically endangered bird may alter some condor behaviors compared to those of the historical population (Walters et al. 2010, USFWS 2013). Despite the difficulties in studying such a wide-ranging species, the primary environmental constraints and mortality factors for condors are now believed to be well known.
In recent years, this species has become symbolic for the use of non-lead ammunitions. Research since the 2000s has confirmed the principal source of lead poisoning in condors is lead ammunition fragments ingested from carcasses (Church et al. 2006, Cade 2007, Hunt et al. 2009, Parish et al. 2009, Finkelstein et al. 2012, Rideout et al. 2012), and these studies have helped lead to California State legislative actions to restrict the use of lead ammunitions (Ridley Tree Condor Conservation Act 2008, AB711 2013). In addition, voluntary outreach efforts to reduce the use of lead ammunitions are active in Arizona and Utah. Unfortunately, these well-intentioned legislative and education efforts have not yet produced a substantial reduction in condor mortality rates from lead poisoning (Rideout et al. 2012, USFWS unpub. data; see also Conservation and Management), let alone the high level of reduction that appears to be needed for viable condor populations (Finkelstein et al. 2012). Because of serious enforcement problems, success in achieving this goal may not be possible with state regulations and voluntary efforts alone and may necessitate national policies that effectively remove the supply of lead ammunitions, as was done with the supply of lead in paint and gasoline. Alternative non-toxic ammunitions, such as copper bullets, serve as excellent alternatives to lead ammunitions, and removal of lead ammunitions can also be expected to have significant health benefits for other wildlife species and for hunters and their associates who consume wild game containing lead shot.