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Federal Register / Vol. 86, No. 55 / Wednesday, March 24, 2021 / Rules and Regulations
offs for condors between these factors and selecting roosts that provide protection from predators Poessel et al.
2018, pp. 4850. While at a roost, condors devote considerable time to preening, sunning, and other maintenance activities Snyder and Snyder 2000, p. 24.
California condors are obligate scavengers and obligate soaring birds, making them reliant on the availability of sufficient food resources and upward air movement Ruxton and Houston 2004, p. 434, Poessel et al. 2018, pp. 36
37. Foraging habitats generally have high landscape productivity, moderate to steep slopes, sparse vegetation, and updrafts necessary to keep California condors aloft Rivers et al. 2014b, pp. 7
9; DElia et al. 2015, p. 96. In coastal areas condors show strong selection for beaches, likely because of the relative abundance of marine mammal carcasses Rivers et al. 2014b, p. 8. A feature of carrion is that dead animals are highly dispersed and ephemeral Ruxton and Houston 2004, p. 433. This exclusive food resource has resulted in evolutionary pressure for condors to be large, obligate soaring birds that forage socially Ruxton and Houston 2004, p.
433. Social foraging means the population is particularly susceptible to contaminated food resources, as a contaminated carcass can poison a large number of individuals in a single feeding Green et al. 2004, pp. 796800;
Green et al. 2008, pp. 69; Finkelstein et al. 2012, p. 11453; DElia and Haig 2013, p. 87.
As birds with a large wingspan that use soaring and gliding flight, California condors can move long distances while expending minimal energy see Pennycuick 1969, pp. 542545; Ruxton and Houston 2004, p. 435; Horvitz et al.
2014, pp. 676678. Examples of exceptional flight distances include:
California condor movements between the central and southern California flocksa distance of approximately 150
miles mi 241 kilometers km e.g., USFWS 2017, pp. 2021; a condor released at Pinnacles National Park flying to the southern Sierra Nevada and backa one-way distance of approximately 249 mi 400 km USFWS, unpublished data; a condor released in the Sierra de San Pedro Martir in Baja California, Mexico, traveling north to San Diego County, a distance of approximately 140 mi 225
km Romo et al. 2012, p. 44; and observations of condors released in northern Arizona traveling to southern Wyoming, Colorado, and New Mexico, at distances of approximately 340 mi 547 km, 400 mi 643 km, and 325 mi 523 km, respectively. In addition, GPS

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telemetry data are now revealing that California condors in southern California are beginning to regularly travel 93124 mi 150200 km away from core use areas USFWS
unpublished data. As the populations continue to grow, the number of longdistance flights is likely to increase.
To date, nests have been concentrated in a relatively limited area around release sites when compared to exceptional flight distances. The farthest nest documented from release sites in each release area is approximately 47 mi 76 km in central California, 57 mi 92
km in southern California, 62 mi 100
km in Arizona/Utah, and 15 mi 24 km in Baja California. We expect that as flock size grows the population will continue to expand and nest sites will eventually be located farther from release sites.
Seasonal shifts in movements to foraging grounds occur with changes in food availability, and perhaps as a result of social factors e.g., traditional movements Meretsky and Snyder 1992, p. 328; Snyder and Snyder 2000, pp. 145147; Hunt et al. 2007, pp. 85
87. There are also seasonal changes in home range, with larger home ranges in late summer and fall compared to late fall and early winter Rivers et al. 2014a, pp. 497, 499.
Life Cycle Breeding California condors form pairs in late fall or early winter and visit various potential nest sites within their nesting territory in January and February Finkelstein et al. 2015, Breeding. Once pairs are formed they tend to stay together year-round for multiple years until one member of the pair dies Snyder and Snyder 2000, p.
19. However, the death of one member of a pair can trigger a chain reaction with multiple pairs switching mates.
This situation can occur because each California condor that loses its mate represents a potentially more desirable mate to individuals of lower rank in the social hierarchy of the flock. Breeding California condors lay a single egg between late January and early April Finkelstein et al. 2015, Breeding. The egg is incubated by both parents and hatches after approximately 5360 days Snyder and Snyder 2000, p. 19.
California condor pairs that lose their egg early in the breeding season February through mid-April will generally lay a replacement egg Snyder and Hamber 1985, p. 377. When a replacement egg is lost, it has occasionally been followed by a third egg Finkelstein et al. 2015, Breeding.
Both parents share responsibilities for feeding the nestling Snyder and Snyder
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2000, p. 19. Feeding, via regurgitation, usually occurs daily for the first 2
months, then gradually diminishes in frequency Snyder and Snyder 2000, p.
197. As early as 6 weeks after hatching, California condor chicks leave the nest cavity but remain in the vicinity of the nest where they are fed by their parents Snyder and Snyder 2000, p. 201. The chick takes its first flight at about 5.5 to 6 months of age but does not become fully independent of its parents until the following year Snyder and Snyder 2000, pp. 201202. Parents occasionally continue to feed a fledgling even after it has begun to make longer flights to foraging grounds Koford 1953, p. 103; Snyder and Snyder 2000, pp.
202203.
Because of the long period of parental care, it was formerly assumed that successful California condor pairs normally nested every other year Koford 1953, pp. 2223. However, this pattern can vary, depending mostly on the time of year that the nestling fledges.
If a nestling fledges relatively early in late summer or early fall, its parents can nest again in the following year, but late fledging may inhibit nesting in the following year Snyder and Hamber 1985, pp. 377378; Snyder and Snyder 2000, p. 19.
Once independent, juvenile California condors often associate with one another on the foraging grounds and join adults and other juveniles at communal roosts Finkelstein et al.
2015, Breeding. In a study of the remnant wild population in southern California 19821987, Meretsky and Snyder 1992, pp. 324325; 329330
found that California condors in their first 2 years after fledging were generally limited to natal nest areas and adjacent foraging areas. Older juveniles would forage more widely, but it was not until age 4 or 5 that condors visited virtually all foraging and nesting areas within a given population. However, more recent data from the reintroduced populations show that fledglings under 1 year of age can be fully integrated into the flock, foraging hundreds of miles from natal or release areas and by 2 years of age some individuals have demonstrated the ability to cover the flocks entire range USFWS, unpublished data. This difference between the remnant wild population in the 1980s and the current population is likely a product of the larger size of the current population, and the larger number of older California condors that are available to serve as mentors to recently fledged condors.

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