California condor

California condor
Temporal range: 2.5–0 Ma
↓

Early Pleistocene – Holocene

At San Diego Zoo, USA
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Cathartiformes
Family: Cathartidae
Genus: Gymnogyps
Lesson, 1842
Species: G. californianus
Binomial name
Gymnogyps californianus
(Shaw, 1797)
Synonyms

Genus-level:

  • Antillovultur Arredondo, 1976
  • Pseudogryphus Ridgway, 1874

Species-level:

  • Vultur californianus Shaw, 1797
  • Gymnogyps amplus L. H. Miller, 1911

The California condor (Gymnogyps californianus) is a New World vulture, the largest North American land bird. This condor became extinct in the wild in 1987 (all remaining wild individuals were captured), but the species has been reintroduced to northern Arizona and southern Utah (including the Grand Canyon area and Zion National Park), the coastal mountains of central and southern California, and northern Baja California. Although other fossil members are known, it is the only surviving member of the genus Gymnogyps. The species is listed as critically endangered by the IUCN.

The plumage is black with patches of white on the underside of the wings; the head is largely bald, with skin color ranging from gray on young birds to yellow and bright orange on breeding adults. Its huge 3.0 m (9.8 ft) wingspan is the widest of any North American bird, and its weight of up to 12 kg (26 lb) nearly equals that of the trumpeter swan, the heaviest among native North American bird species. The condor is a scavenger and eats large amounts of carrion. It is one of the world's longest-living birds, with a lifespan of up to 60 years.[2]

Condor numbers dramatically declined in the 20th century due to poaching, lead poisoning, and habitat destruction.[3] A conservation plan was put in place by the United States government that led to the capture of all the remaining wild condors which was completed in 1987, with a total population of 27 individuals. These surviving birds were bred at the San Diego Zoo Safari Park and the Los Angeles Zoo. Numbers rose through captive breeding and, beginning in 1991, condors were reintroduced into the wild. The California condor is one of the world's rarest bird species: as of October 2014 there are 425 condors living wild or in captivity.[4] The condor is a significant bird to many Californian Native American groups and plays an important role in several of their traditional myths.

Taxonomy

California condor skull

The California condor was described by English naturalist George Shaw in 1797 as Vultur californianus. It was originally classified in the same genus as the Andean condor (V. gryphus), but, due to the Andean condor's slightly different markings, slightly longer wings, and tendency to kill small animals to eat,[5] the California condor has now been placed in its own monotypic genus. The generic name Gymnogyps is derived from the Greek gymnos/γυμνος "naked" or "bare", and gyps/γυψ "vulture",[6] while the specific name californianus comes from its location in California. The word condor itself is derived from the Quechua word kuntur.[7]

The exact taxonomic placement of the California condor and the other six species of New World vultures remains unclear.[8] Though similar in appearance and ecological roles to Old World vultures, the New World vultures evolved from a different ancestor in a different part of the world. Just how different the two are is currently under debate, with some earlier authorities suggesting that the New World vultures are more closely related to storks.[9] More recent authorities maintain their overall position in the order Falconiformes along with the Old World vultures[10] or place them in their own order, Cathartiformes.[11] The South American Classification Committee has removed the New World vultures from Ciconiiformes and instead placed them in Incertae sedis, but notes that a move to Falconiformes or Cathartiformes is possible.[8]

Evolutionary history

Fossil of the extinct species Gymnogyps amplus from the La Brea Tar Pits

The genus Gymnogyps is an example of a relict distribution. During the Pleistocene epoch, this genus was widespread across the Americas. From fossils, the Floridan Gymnogyps kofordi from the Early Pleistocene and the Peruvian Gymnogyps howardae from the Late Pleistocene have been described.[12] A condor found in Late Pleistocene deposits on Cuba was initially described as Antillovultur varonai, but has since been recognized as another member of Gymnogyps, Gymnogyps varonai. It may even have derived from a founder population of California condors.[13]

Today's California condor is the sole surviving member of Gymnogyps and has no accepted subspecies. However, there is a Late Pleistocene form that is sometimes regarded as a palaeosubspecies, Gymnogyps californianus amplus. Current opinions are mixed regarding the classification of the form as a chronospecies or a separate species Gymnogyps amplus.[14] Gymnogyps amplus occurred over much of the bird's historical range – even extending into Florida – but was larger, having about the same weight as the Andean condor. This bird also had a wider bill.[15] As the climate changed during the last ice age, the entire population became smaller until it had evolved into the Gymnogyps californianus of today,[16][17] although more recent studies by Syverson query that theory.[14]

Description

Adult in flight. Tracking tags can be seen on both wings.

The adult California condor is a uniform black with the exception of large triangular patches or bands of white on the underside of the wings. It has gray legs and feet, an ivory-colored bill, a frill of black feathers surrounding the base of the neck, and brownish red eyes.[18] The juvenile is mostly a mottled dark brown with blackish coloration on the head. It has mottled gray instead of white on the underside of its flight feathers.[19]

The condor's head and neck have few feathers, and the skin of the head and neck is capable of flushing noticeably in response to emotional state, a capability that can serve as communication between individuals.[20] The skin color varies from yellowish to a glowing reddish-orange.[18] The birds do not have true syringeal vocalizations. They can make a few hissing or grunting sounds only heard when very close.[21]

Upper body

Contrary to the usual rule among true birds of prey, the female is slightly smaller than the male. Overall length can range from 109 to 140 cm (43 to 55 in) and wingspan from 2.49 to 3 m (8.2 to 9.8 ft). Their weight can range from 7 to 14.1 kg (15 to 31 lb), with estimations of average weight ranging from 8 to 9 kg (18 to 20 lb).[19][22] Wingspans of up to 3.4 m (11 ft) have been reported but no wingspan over 3.05 m (10.0 ft) has been verified.[23] Most measurements are from birds raised in captivity, so determining if there are any major differences in measurements between wild and captive condors is difficult.

California condors have the largest wingspan of any North American bird. They are surpassed in both body length and weight only by the trumpeter swan and the introduced mute swan. The American white pelican and whooping crane also have longer bodies than the condor. Condors are so large that they can be mistaken for a small, distant airplane, which possibly occurs more often than they are mistaken for other species of bird.[24]

The middle toe of the California condor's foot is greatly elongated, and the hind one is only slightly developed. The talons of all the toes are straight and blunt, and are thus more adapted to walking than gripping. This is more similar to their supposed relatives the storks[25][26] than to birds of prey and Old World vultures, which use their feet as weapons or organs of prehension.

Historic range

California oak savanna on the east flank of Sonoma Mountain

At the time of human settlement of the Americas, the California condor was widespread across North America; condor bones from the late Pleistocene have been found at the Cutler Fossil Site in southern Florida.[27] However, climate changes associated with the end of the last glacial period and the extinction of the Pleistocene megafauna led to a subsequent reduction in range and population. Five hundred years ago, the California condor roamed across the American Southwest and West Coast. Faunal remains of condors have been found documented in Arizona,[28] Nevada,[29] New Mexico,[30][31] and Texas.[32] The Lewis and Clark Expedition of the early 19th century reported on their sighting and shooting of California condors near the mouth of the Columbia River.[33][34]

Habitat

The condors live in rocky shrubland, coniferous forests, and oak savannas.[1] They are often found near cliffs or large trees, which they use as nesting sites. Individual birds have a huge range and have been known to travel up to 250 km (160 mi) in search of carrion.

There are two sanctuaries dedicated to this bird, the Sisquoc Condor Sanctuary in the San Rafael Wilderness[35] and the Sespe Condor Sanctuary in the Los Padres National Forest. These areas were chosen because of their prime condor nesting habitat.

Ecology and behavior

Preening condors

When in flight, the movements of the condor are remarkably graceful. The lack of a large sternum to anchor their correspondingly large flight muscles restricts them to being primarily soarers. The birds flap their wings when taking off from the ground, but after attaining a moderate elevation they largely glide, sometimes going for miles without a single flap of their wings. They have been known to fly up to speeds of 90 km/h (56 mph) and as high as 4,600 m (15,100 ft).[36] They prefer to roost on high perches from which they can launch without any major wing-flapping effort. Often, these birds are seen soaring near rock cliffs, using thermals to aid them in keeping aloft.[37]

The California condor has a long life span, reaching up to 60 years.[2][3] If it survives to adulthood, the condor has few natural threats other than humans.[38] Because they lack a syrinx, their vocal display is limited to grunts and hisses.[20] Condors bathe frequently and can spend hours a day preening their feathers.[36] Condors also perform urohidrosis, or defecate on their legs, to reduce their body temperature.[20] There is a well-developed social structure within large groups of condors, with competition to determine a pecking order decided by body language, competitive play behavior, and a variety of hisses and grunts. This social hierarchy is displayed especially when the birds feed, with the dominant birds eating before the younger ones.[39]

Diet

Juveniles feeding

Wild condors maintain a large home range, often traveling 250 km (160 mi) a day in search of carrion.[40] It is thought that in the early days of its existence as a species, the California condor lived off the carcasses of the "megafauna", which are now extinct in North America. They still prefer to feast on large, terrestrial mammalian carcasses such as deer, goats, sheep, donkeys, horses, pigs, cougars, bears, or cattle. Alternatively, they may feed on the bodies of smaller mammals, such as rabbits or coyotes, aquatic mammals such as whales and California sea lions, or salmon. Bird and reptile carcasses are rarely eaten. Since they do not have a sense of smell,[41] they spot these corpses by looking for other scavengers, like eagles and smaller vultures, the latter of which cannot rip through the tougher hides of these larger animals with the efficiency of the larger condor. They can usually intimidate other scavengers away from the carcass, with the exception of bears, which will ignore them, and golden eagles, which will fight a condor over a kill or a carcass.[18] In the wild they are intermittent eaters, often going for between a few days to two weeks without eating,[40] then gorging themselves on 1–1.5 kilograms (2.2–3.3 lb) of meat at once.

Reproduction

An adult with a 30-day-old chick in a cave nest near Hopper Mountain National Wildlife Refuge, California, USA

Condors begin to look for a mate when they reach sexual maturity at the age of six.[36] To attract a prospective mate, the male condor performs a display, in which the male turns his head red and puffs out his neck feathers. He then spreads his wings and slowly approaches the female. If the female lowers her head to accept the male, the condors become mates for life.[39] The pair makes a simple nest in caves or on cliff clefts, especially ones with nearby roosting trees and open spaces for landing. A mated female lays one bluish-white egg every other year. Eggs are laid as early as January to as late as April.[42] The egg weighs about 280 grams (10 oz) and measures from 90 to 120 mm (3.5 to 4.7 in) in length and about 67 mm (2.6 in) in width. If the chick or egg is lost or removed, the parents "double clutch", or lay another egg to take the lost one's place. Researchers and breeders take advantage of this behavior to double the reproductive rate by taking the first egg away for puppet-rearing; this induces the parents to lay a second egg, which the condors are sometimes allowed to raise.[43]

The eggs hatch after 53 to 60 days of incubation by both parents. Chicks are born with their eyes open and sometimes can take up to a week to leave the shell completely.[20] The young are covered with a grayish down until they are almost as large as their parents. They are able to fly after five to six months, but continue to roost and forage with their parents until they are in their second year, at which point the parents typically turn their energies to a new nest.[18] Ravens are the main predatory threat to condor eggs, while golden eagles and bears are potential predators of condor offspring.

Conservation

A juvenile in the Grand Canyon, with its numbered tag prominent.

Obstacles to recovery

In modern times, a wide variety of causes have contributed to the condor's decline. Its low clutch size (one young per nest), combined with a late age of sexual maturity, make the bird vulnerable to artificial population decline. Significant past damage to the condor population has also been attributed to poaching, especially for museum specimens,[44] lead poisoning (from eating animals containing lead shot),[45] DDT poisoning,[46] electric power lines, egg collecting, and habitat destruction. During the California Gold Rush, some condors were even kept as pets.[47] The leading cause of mortality in nestling condors is the ingestion of trash that is fed to them by their parents.[48]

In addition to this, cattle ranchers who observed condors feeding on the dead young of their cattle assumed that the birds killed the cattle. This fallacy led to the condor's extirpation in some parts of the western United States. This belief was so deeply ingrained that the reintroduction of condors to the Grand Canyon was challenged by some cattle ranchers, who mistakenly believed that the bird hunted calves and lambs.[49]

Unanticipated deaths among recent condor populations occurred due to contact with golden eagles, lead poisoning, and other factors such as power line collisions.[50] Since 1994, captive-bred California condors have been trained to avoid power lines and people. Since the implementation of this aversion conditioning program, the number of condor deaths due to power lines has greatly decreased.[51] Lead poisoning due to fragmented lead bullets in large game waste is a particularly big problem for condors due to their extremely strong digestive juices; lead waste is not as much of a problem for other avian scavengers such as the turkey vulture and common raven.[52] This problem has been addressed in California by the Ridley-Tree Condor Preservation Act, a bill that went into effect July 1, 2008 that requires that hunters use non-lead bullets when hunting in the condor's range.[53] Blood lead levels in golden eagles as well as turkey vultures has declined with the implementation of the Ridley-Tree Condor Preservation Act, demonstrating that the legislation has helped reduce other species' lead exposures aside from the California condor.[54][55]

In an article titled: "Condors or lead ammunition? We can't have both" published by The Ecologist in January 2015, author Dawn Starin states: "Over 60% of the adult and juvenile deaths (that is, excluding chicks and fledglings) in the wild population have been as a result of lead poisoning."[56] She continues: "Because condors have been known to live past the age of 50, do not breed until they are at least six years old, and raise only one chick every other year, their populations cannot withstand the mortality rates caused by this neurological toxin."[56] According to epidemiologist Terra Kelly: "Until all natural food sources are free from lead-based ammunition, lead poisoning will threaten recovery of naturally sustaining populations of condors in the wild."[56] The article also states: "The military doesn't use lead, and if that isn't a huge message I don't know what is."[56] However, this statement must be taken in the context that the military has limited the use of lead ammunition at installations in the condor's range, not service wide.

California Condor Recovery Plan

Condor chick being fed by condor feeding puppet

As the condor's population continued to decline, discussion began about starting a captive breeding program for the birds. Opponents to this plan argued that the condors had the right to freedom, that capturing all of the condors would change the species' habits forever, and that the cost was too great.[57] However, the project received the approval of the United States government, and the capture of the remaining wild condors was completed on Easter Sunday 1987, when AC-9, the last wild condor, was captured.[58] There were only 22 condors in existence, all in captivity.

The goal of the California Condor Recovery Plan was to establish two geographically separate populations, one in California and the other in Arizona, each with 150 birds and at least 15 breeding pairs. As the Recovery Program works toward this goal the number of release sites has grown. There are three active release sites in California, one in Arizona and one in Baja California, Mexico.[59]

The captive breeding program, led by the San Diego Wild Animal Park and Los Angeles Zoo, got off to a slow start due to the condor's mating habits. However, utilizing the bird's ability to double clutch, biologists began removing the first egg from the nest and raising it with puppets, allowing the parents to lay another egg.

As the number of condors grew, attention began to focus on releasing some back into the wild. In 1988, the United States Fish and Wildlife Service began a reintroduction experiment involving the release of captive Andean condors into the wild in California. Only females were released, to eliminate the possibility of accidentally introducing a South American species into the United States. The experiment was a success, and all the Andean condors were recaptured and re-released in South America.[36] California condors were released in 1991 and 1992 in California, and again in 1996 in Arizona near the Grand Canyon.[19] Though the birth rate remains low in the wild, their numbers are increasing steadily through regular releases of captive-reared adolescents.

A USFWS sign at Bitter Creek National Wildlife Refuge, California, USA

The California condor conservation project may be one of the most expensive species conservation projects in United States history,[60] costing over $35 million, including $20 million in federal and state funding, since World War II.[61] As of 2007 the annual cost for the condor conservation program was around $2.0 million per year.[61] However, nesting milestones have been recently reached by the reintroduced condors. In 2003, the first nestling fledged in the wild since 1981.[49] In March 2006, a pair of California condors, released by Ventana Wildlife Society, attempted to nest in a hollow tree near Big Sur, California. This was the first time in more than 100 years in which a pair of California condors had been seen nesting in Northern California.[62] As of November 2011 there were 394 individuals living, including 205 in the wild[2][3] and the rest in the San Diego Wild Animal Park, the Los Angeles Zoo, the Oregon Zoo, and the World Center for Birds of Prey in Boise, Idaho. As of October 2010, the wild condor population in its name state of California reached 100 individuals, and 73 wild condors in Arizona.[59] As of May 2012, the number of living individuals has reached 405, with 179 living in captivity.[63] By June 2014, using data from the National Park Service, the condor population had reached 439: 225 in the wild and 214 in captivity.[64] Official statistics from the October 2014 USFWS record an overall population of 425, of which 219 are wild and 206 are captive.[4]

As the Recovery Program achieved milestones, a fifth active release site in Sierra de San Pedro Mártir National Park, Baja California, Mexico, was added to the three release sites in California (Big Sur, Pinnacles National Park and Bitter Creek National Wildlife Refuge) and the Vermilion Cliffs release site in Arizona.[65][66] In early 2007, a California condor laid an egg in Mexico for the first time since at least the 1930s.[67] The population of the condors has risen due to these wild and also captive nestings. In the spring of 2009, a second wild chick was born in the Sierra de San Pedro Mártir National Park and was named Inyaa ("Sun" in the Kiliwa language) by local environmentalists.[68] In 2014, Condor #597, also known as "Lupine", was spotted near Pescadero, a coastal community south of San Francisco.[69] Lupine had been routinely seen at Pinnacles National Park after having been released into the wild at Big Sur the previous year. Younger birds of the Central California are seeking to expand their territory, which could mean that a new range expansion is possible for the more than 60 condors flying free in central California.[70] Also in 2014 the first successful breeding in Utah was reported. A pair of condors, who were released in Arizona, nested in Zion National Park and the hatching of one chick was confirmed.[71]

Pinnacles National Park, a release site.

Condor Watch

Zooniverse icon for Condor Watch

A crowdsourcing project called Condor Watch (CW) was started on April 14, 2014, hosted by the web portal Zooniverse.[72][73] Volunteers are asked to examine motion-capture images of California condors associated with release sites managed by the United States Fish and Wildlife Service, National Park Service and Ventana Wildlife Society. The tasks on the website include identifying tagged condors and marking the distance to feeding sources such as animal carcasses. Biologists can then use this data to deduce which birds are at risk of lead poisoning.

Condor Watch enables volunteers, or citizen scientists, to participate in active research. The project has up 175,000 images to view and assess—far more than the team could hope to view on their own.[72] Lead scientist Myra Finkelstein believes volunteering is fun because it allows enthusiasts to track the "biographies" of individual condors. Citizen science has long been used in ornithology, for instance in the Audubon Society's Christmas Bird Count, which began in 1900 and the breeding bird survey which began in 1966. McCaffrey (2005) believes this approach not only directly benefits ongoing projects, but will also help train aspiring ornithologists.[74]

Relationship with humans

Condor on 2005 commemorative coin

Throughout its historic range, the California condor has been a popular subject of mythology and an important symbol to Native Americans. Unusually,[75] this bird takes on different roles in the storytelling of the different tribes.

The Wiyot tribe of California say that the condor recreated mankind after Above Old Man wiped humanity out with a flood.[76] However, other tribes, such as California's Mono, viewed the condor as a destroyer, not a creator. They say that Condor seized humans, cut off their heads, and drained their blood so that it would flood Ground Squirrel's home. Condor then seized Ground Squirrel after he fled, but Ground Squirrel managed to cut off Condor's head when Condor paused to take a drink of the blood.[77] According to the Yokut tribe, the condor sometimes ate the moon, causing the lunar cycle, and his wings caused eclipses.[78] The Chumash tribe of Southern California believed that the condor was once a white bird, but it turned black when it flew too close to a fire.[78]

Condor bones have been found in Native American graves, as have condor feather headdresses. Cave paintings of condors have also been discovered.[79] Some tribes ritually killed condors to make ceremonial clothing out of their feathers. Shamans then danced while wearing these to reach the upper and lower spiritual worlds. Whenever a shaman died, his clothes were said to be cursed,[80] so new clothing had to be made for his successor. Some scientists, such as Noel Snyder, believe that this process of making ceremonial clothing contributed to the condor's decline.[80]

References

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  2. 1 2 3 "Once nearly extinct, the California condor nears new milestones". CNN. April 27, 2011.
  3. 1 2 3 "San Diego Zoo's Animal Bytes: California Condor". The Zoological Society of San Diego's Center for Conservation and Research for Endangered Species. Retrieved April 18, 2012.
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  13. ↑ Suárez, W.; Emslie, S.D. (2003). "New fossil material with a redescription of the extinct condor Gymnogyps varonai (Arredondo, 1971) from the Quaternary of Cuba (Aves: Vulturidae)" (PDF). Proceedings of the Biological Society of Washington 116 (1): 29–37.
  14. 1 2 V.J. Syverson (2007). "Evolutionary Patterns in Pleistocene to Recent California Condors". Geological Society of America 39 (6).
  15. ↑ Fisher, Harvey L. (1944). "The skulls of the Cathartid vultures" (PDF). Condor 46 (6): 272–296. doi:10.2307/1364013. JSTOR 1364013.
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  20. 1 2 3 4 "California Condors Cool Facts". Ventana Wildlife Society. Retrieved August 14, 2007.
  21. ↑ Snyder, Noel; Snyder, Helen (2000). The California Condor: A Saga of Natural History & Conservation. San Diego, California: Academic Press. p. 5. ISBN 0-12-654005-5.
  22. ↑ Raptors of the World by Ferguson-Lees, Christie, Franklin, Mead & Burton. Houghton Mifflin (2001), ISBN 0-618-12762-3
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  29. ↑ Miller, Loye (1931). "The California Condor in Nevada" (PDF). Condor 33 (1): 32. doi:10.2307/1363932.
  30. ↑ Wetmore, Alexander (1931). "The California Condor in New Mexico" (PDF). Condor 33 (2): 76–77. doi:10.2307/1363313.
  31. ↑ Wetmore, Alexander (1932). "Additional Records of Birds from Cavern Deposits in New Mexico" (PDF). Condor 34 (3): 141–142. doi:10.2307/1363542.
  32. ↑ Wetmore, Alexander & Friedmann, Herbert (1938). "The California Condor in Texas" (PDF). Condor 35 (1): 37–38. doi:10.2307/1363462.
  33. ↑ Majors, Harry M. (1975). Exploring Washington. Van Winkle Publishing Co. p. 114. ISBN 978-0-918664-00-6.
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  35. ↑ Gagnon, Dennis R. Hiking the Santa Barbara Backcountry. The Ward Ritchie Press, Pasadena, California, 1974. ISBN 0-378-03542-8
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  37. ↑ Nielsen 2006, p. 79
  38. ↑ "San Diego Zoo's Animal Bytes: California Condor". Zoological Society of San Diego. Retrieved August 14, 2007.
  39. 1 2 "California Condor Behavior". U.S. Fish and Wildlife Service, Hopper Mountain National Wildlife Refuge. Archived from the original on April 16, 2007. Retrieved August 22, 2007.
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  42. ↑ Snyder, Noel; Snyder, Helen (2000). The California Condor. Academic Press. ISBN 0-12-654005-5.
  43. ↑ Nielsen 2006, p. 186
  44. ↑ Nielsen 2006, p. 83
  45. ↑ Church, ME; Gwiazda, R; Risebrough, RW; Sorenson, K; Chamberlain, CP; Farry, S; Heinrich, W; Rideout, BA; Smith, DR (2006). "Ammunition is the Principal Source of Lead Accumulated by California Condors Re-Introduced to the Wild". Environmental Science Technology 40 (19): 6143–50. doi:10.1021/es060765s. PMID 17051813.
  46. ↑ Kiff, L. F.; Peakall, D. B. & Wilbur, S. R. (1979). "Recent Changes in California Condor Eggshells" (PDF). Condor 81 (2): 166–172. doi:10.2307/1367284. JSTOR 1367284.
  47. ↑ Nielsen 2006, p. 88
  48. ↑ Rideout, BA; Stalis, I; Papendick, R; Pessier, A; Puschner, B; Finkelstein, ME; Smith, DR; Johnson, M; Mace, M; Stroud, R; Brandt, J; Burnett, J; Parish, C; Petterson, J; Witte, C; Stringfield, C; Orr, K; Zuba, J; Wallace, M; Grantham, J (2012). "Patterns of mortality in free-ranging California Condors (Gymnogyps californianus)" (PDF). Journal of wildlife diseases 48 (1): 95–112. doi:10.7589/0090-3558-48.1.95. PMID 22247378.
  49. 1 2 Sheppard, Brad. "Condors". Sheppard Software. Retrieved August 27, 2007.
  50. ↑ milius, susan (June 26, 2012). "Lead poisoning stymies condor recovery". sciencenews. Retrieved August 24, 2014.
  51. ↑ "California Condor Recovery Program". U.S. Fish and Wildlife Service, Hopper Mountain National Wildlife Refuge. December 2006. Archived from the original on September 11, 2007. Retrieved September 13, 2007.
  52. ↑ Thacker, Paul D.; Lubick, Naomi; Renner, Rebecca; Christen, Kris; Pelley, Janet (2006). "Condors are shot full of lead". Environmental Science & Technology 40 (19): 5826–5831. doi:10.1021/es063001l.
  53. ↑ "Assembly Bill No. 821" (PDF). CA State Senate. Retrieved July 3, 2008.
  54. ↑ Kelly, Terra R.; Peter H. Bloom; Stever G. Torres; Yvette Z. Hernandez; Robert H. Poppenga; Walter M. Boyce; Christine K. Johnson (2011). Iwaniuk, Andrew, ed. "Impact of the California Lead Ammunition Ban of Reducing Lead Exposures in Golden Eagles and Turkey Vultures". PLoS ONE 6 (4): e17656. doi:10.1371/journal.pone.0017656. PMC 3071804. PMID 21494329.
  55. ↑ Taylor, Dennis L. (May 8, 2014) "Lead ammo deadly beyond the target" The Californian (Salinas, CA)
  56. 1 2 3 4 Dawn Starin (21 January 2015). "Condors or lead ammunition? We can't have both". The Ecologist. Retrieved 26 January 2015.
  57. ↑ Nielsen 2006, p. 13
  58. ↑ Nielsen 2006, p. 24
  59. 1 2 Weise, Elizabeth (October 7, 2010). "Condor population reaches 100 in California". USA Today. Retrieved October 7, 2010.
  60. ↑ Nielsen 2006, p. 7
  61. 1 2 "Frequently Asked Questions". U.S. Fish and Wildlife Service, Hopper Mountain National Wildlife Refuge. Archived from the original on August 8, 2007. Retrieved August 23, 2007.
  62. ↑ "Fresh Hope For Condors". Sky News. March 30, 2006. Retrieved August 14, 2007.
  63. ↑ Muldoon, Katy (May 20, 2012). "California Condors Hit a Milestone – a Population of 405 – after Nearly Going Extinct.". The Oregonian. Retrieved May 20, 2012.
  64. ↑ "California Condor Recovery Program (monthly status report)" (PDF). National Park Service. 30 June 2014. Retrieved 31 August 2014.
  65. ↑ "Condors to take flight in Baja Sierras". UCMEXUS (University of California Institute for Mexico and the United States). Spring 2003. Retrieved October 7, 2010.
  66. ↑ "FAQ About California Condors". Santa Barbara Zoo. April 15, 2009. Retrieved February 17, 2011.
  67. ↑ Watkins, Thomas (April 3, 2007). "California Condor lays egg in Mexico". Associated Press via USA Today. Retrieved August 14, 2007.
  68. ↑ Galindo, Yadira (June 18, 2009). "Condor Chick Hatches in Mexican Wilderness". California Condor Conservation. Retrieved March 1, 2011.
  69. ↑ P. Rogers (14 June 2014). "First California condor spotted in San Mateo County since 1904". Vallejo Times Herald. Retrieved 28 August 2014.
  70. ↑ Banks, Alicia (June 16, 2014) "Condor spotted in San Mateo County is first in 110 years" Los Angeles Times
  71. ↑ National Park Service: Zion National Park – Biologists Catch First Glimpse of Condor Chick in Utah, July 15, 2014
  72. 1 2 Stephens, Tim (April 15, 2014). "'Condor Watch' enlists citizen scientists to help an endangered species". University of California. Retrieved August 21, 2014.
  73. ↑ "'Condor watch' enlists citizen scientists to help endangered species". sciencedaily. April 15, 2014. Retrieved August 19, 2014.
  74. ↑ McCaffrey, R.E. (2005). Using Citizen Science in Urban Bird Studies. Urban Habitats. 3 (1). p. 70-86.
  75. ↑ Nielsen 2006, p. 39
  76. ↑ Nielsen 2006, p. 37
  77. ↑ Nielsen 2006, p. 38
  78. 1 2 Nielsen 2006, p. 40
  79. ↑ Nielsen 2006, p. 36
  80. 1 2 Nielsen 2006, p. 41

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