Release captive-bred individuals to re-establish or boost populations in native range
Overall effectiveness category Beneficial
Number of studies: 31
Background information and definitions
Captive breeding is normally used to provide individuals which can then be released into the wild (often called ‘reintroduction’) to either re-establish a population that has been lost, or to augment an existing population (‘restocking’).
Release techniques vary considerably, from ‘hard releases’ involving the simple release of individuals into the wild to ‘soft releases’ which involve a variety of adaptation and acclimatisation techniques before release or post-release feeding and care. This action includes studies describing the effects of release programmes for captive-bred or captive-reared mammals that do not provide details of specific release techniques. Studies that describe or compare specific release techniques, such as use of holding pens at release sites, or providing supplementary food, water or artificial refuges/breeding sites are described under each specific action.
This action includes studies where animals were released in groups but not studies where releases of different group sizes were compared, or where animals were released in family or social groups (including groups where social animals have been pre-conditioned together prior to release in holding pens). For those studies, see Release translocated/captive-bred mammals in larger unrelated groups and Release translocated/captive-bred mammals in family/social groups.
Supporting evidence from individual studies
A replicated, controlled study in 1990–1992 at two grassland sites in Alberta, Canada (Carbyn et al. 1994) found that captive-born swift foxes Vulpes velox had lower post-release survival rates than did translocated, wild-born animals. No statistical analyses were performed. Nine months after release into the wild, at least two out of 27 (7%) captive-born swift foxes were known to be alive, compared with twelve out of 28 (43%) wild-born translocated swift foxes. In May 1990 and 1991, a total of 27 captive-born and 28 wild-born swift foxes were released simultaneously. Wild-born animals had been captured in Wyoming, USA, 4–7 months before release and were quarantined for ≥30 days. Animals were released without prior conditioning in holding pens. Foxes were radio-collared and monitored from the ground and air, for at least nine months.Study and other actions tested
Referenced paperCarbyn L.N., Armbruster H.J. & Mamo C. (1994) The swift fox reintroduction program in Canada from 1983 to 1992. Pages 247-271 in: M.L. Bowles & C.J. Whelan (eds.) Restoration of endangered species: conceptual issues, planning and implementation. Cambridge University Press, Cambridge, UK.
A study in 1993–1995 in northern Florida, USA (Belden & McCown 1996) found that following release, most captive-bred and translocated mountain lions Puma concolor stanleyana that had been held in captivity prior to release established home ranges in the release area. Of 19 released mountain lions, 15 established one or more home ranges. Post-release survival periods for these 15 animals are not stated but two were killed (one illegally shot and one killed by a vehicle) and two were recaptured due to landowner concerns or concerns for their survival, 37–140 days after release. Nineteen mountain lions were released in northern Florida in 1993–1994. Six animals were captive-bred, 10 were wild-caught and released within three months and three were caught and released after 3–8 years. mountain lions were radio-tracked daily in February 1993–April 1993 and then for three days/week until June 1995.Study and other actions tested
A replicated, controlled study in 1989–1993 in two rivers in southern Sweden (Sjöåsen 1996; same experimental set-up as Sjöåsen 1997) found that captive-bred European otters Lutra lutra released into the wild had a lower survival rate than did wild-born translocated otters. One year after release, the survival rate of captive-bred otters (42%) was lower than that of wild-born translocated otters (79%). Additionally, captive-bred otters with a shorter (5–48 day) period between separation from their mother and release to the wild had a higher survival rate (80%) than individuals with a longer (49–98 day) period (13%). Between 1989 and 1992, twenty-five captive-bred and 11 wild-born otters were released into two rivers. Thirty-four otters were released in one river catchment and two in the other. Captive-bred otters were descendants of two captive females. Wild-born otters were live-trapped along the Norwegian coast. All otters were around one year old when released. All except one were released between February and June. All were fitted with an implanted radio-transmitter and monitored for one year on 64% of days.Study and other actions tested
A study in 1991–1995 in a desert reserve in central Saudi Arabia (Dunham 1997) found that nearly half of captive-bred mountain gazelles Gazella gazella released into the wild survived more than two years, and the population bred successfully and more than doubled in size. Of a total of 71 released gazelles, 69–73% survived over one year and 58–59% survived over two years. Mortality was high in the first month after release (13% died), but the mean annual survival rate of gazelles which survived the first month was 78%. Gazelles that were over three years of age when released were more likely to die within 54 weeks of release than younger animals (54% vs 19% mortality) due to a higher rate of predation by wolves. Released females gave birth to at least 134 calves, of which at least 107 were conceived in the wild. By December 1994, the population had increased to 152–185 animals. Between January 1991 and June 1993, seventy-one captive-born mountain gazelles were released into three valleys inside a 2,000-km2 reserve. The valleys were fenced to exclude domestic camels but allowed movement of gazelles. All released individuals were ear-tagged and 28 were fitted with a radio-collar. Gazelles were monitored using binoculars and a telescope on 396 days between January 1991 and June 1995. Gazelles were provided with water year-round.Study and other actions tested
A study in 1992–1993 in a mountain area dominated by deciduous forest in northern Italy (Pandini & Cesaris 1997) found that two captive-bred roe deer Capreolus capreolus that were released into the wild survived for at least 10 months. Both captive-bred roe deer survived over 10 months post-release (long term survival is not reported). Their average annual home range extended over 38.5 ha. In November 1992, the two captive-bred male roe deer (aged 17 months) were radio-tagged and released into the wild. The release site was within a 400-ha area with a roe deer population density of 0.2 deer/ha. The area was dominated by deciduous coppice (45%), mixed crops (21%), urbanized areas (14%) and meadows and pastures (13%). The two roe deer were radio-tracked for 10 months after release until September 1993.Study and other actions tested
A study in 1989–1992 at seven lakes in boreal forest in Sweden (Sjöåsen 1997; same experimental set-up as Sjöåsen 1996) found that following release, at least 14 of 36 captive-bred or wild-born translocated European otters Lutra lutra survived for at least one to two years. Fourteen otters had established home ranges and were still alive when last recorded, 362–702 days after release. Eight further otters were monitored until their transmitters failed or they moved out of radio contact, 89–219 days after release. Fourteen were known to have died, 18–750 days after release. Otter origin (captive-bred or wild-caught) did not affect movement distance. In 1989–1992, thirty-six otters (25 captive-bred and 11 wild-born, translocated otters) were released in lakes and rivers in southern Sweden. Otters were fitted with radio-transmitters. Radio-tracking was carried out at least monthly, in 1989–1992.Study and other actions tested
A study in 1982–1997 in a mountain forest reserve in Tennessee, USA (Stiver et al. 1997) found that at least 10 of 23 captive-bred American black bears Ursus americanus released into the wild were killed or had to be removed. Ten of 23 captive-bred black bears (43%) survived for an average of 172 days after release (range 4–468 days) before being killed (seven bears), euthanised after being hit by a vehicle (one bear), relocated (one bear) or returned to captivity (one bear). The fate of the 13 other released bears is not known (one tracked bear lost its radio-collar after 484 days, 12 bears were not radio-tracked or observed again after release). Twenty-three captive-bred, pen-reared black bears (11 male, 12 female; average 2.5 years old) were released in 1982–1995 at five sites in which bear hunting was prohibited in the Cherokee National Park. All bears were individually marked with ear-tags and/or tattoos. Seven were radio-collared and monitored an average of once every 18 days from an aircraft in 1983–1997.Study and other actions tested
A review of studies in 1989–1991 in prairie sites in Canada and the USA (Smeeton & Weagle 2000) found that following release, captive-bred swift foxes Vulpes velox had lower survival rates than did translocated, wild-caught swift foxes. Over an unspecified time period, 59% of wild-caught translocated swift foxes survived while three of 41 (7%) captive-bred swift foxes survived after release. In 1989–1991, thirty-three wild-caught, adult foxes and 41 captive-bred foxes, born the previous year, were released in the spring. Methods used for monitoring animals were unclear.Study and other actions tested
A replicated study in 1993–2002 in seven forest sites across England, UK (Bright & Morris 2002) found that following releases of captive-bred (and some translocated wild-born) dormice Muscardinus avellanarius, populations persisted for between three months and over seven years and reproduced. In at least three of seven releases, dormouse populations were stable or increased from 19–57 released individuals to 40–55 individuals between two and seven years later. At one site, only one individual was detected 7–8 years after the release of 52 individuals in two batches. In three populations, the number of released animals is not provided, but populations persisted for at least three months and up to at least three years after release. Animals in all seven populations bred in the wild. Releases took place in 1993–2000 into woodlands in Cambridgeshire, Nottinghamshire, Cheshire, Warwickshire, Buckinghamshire, Yorkshire and Suffolk. Monitoring continued until 2000–2002. Precise numbers and origins of dormice released are not given for all sites. Most were captive-bred but some were wild-born translocated animals. Some dormice were kept in pre-release holding pens, sometimes for several weeks, before release. Nest boxes and supplementary food were provided at least at some sites. See paper for further details.Study and other actions tested
A replicated study in 1992–2000 on two rivers in Hertfordshire, UK (Copp & Roche 2003) found that a population of released captive-bred European otters Lutra lutra persisted for over eight years after release. Eight years after release of six captive-bred otters into rivers with no otter populations, otters were still detected in the release area. Over this time, the range used by released otters expanded, but some of this may have been due to natural recolonization. At least one otter died during the study period. In October–December 1991, six captive-bred otters were released in two rivers with no known otter populations. Individuals were approximately two years old when released. The range and persistence of the populations were assessed by surveying droppings through to February 2000.Study and other actions tested
A review of 14 releases of six species of captive-bred mammals in Western Australia, Australia (Mawson 2004) found that where outcomes were available for release programmes, over half were regarded as successful. One out of two releases of rufous hare-wallabies Lagorchestes hirsutus, one out of two of dibblers Parantechinus apicalis and one out of four of western quolls Dasyurus geoffroii were classed as successful. However, the only release of banded hare-wallabies Lagostrophus fasciatus and one out of two releases of rufous hare-wallabies Lagorchestes hirsutus were classed as unsuccessful. At the time of the review, the outcomes of two releases of bilbies Perameles lagotis, three of western quolls, one of dibblers and three of Shark Bay mouse Pseudomys fieldi remained uncertain. In 1993–2002, sixteen to 149 captive-bred mammals were released per location. One translocation of Shark Bay mouse was partially sourced from wild stock. Invasive mammals were controlled at some release sites. The definition of successful reintroduction was not stated for most species but, for others, it included measures of population increase and persistence.Study and other actions tested
A study in 2002–2005 in two wetland areas in the Netherlands (Lammertsma et al. 2006) found that following release of captive-bred animals, together with the release of some translocated individuals, over half of Eurasian otters Lutra lutra settled in their release areas and some successfully reproduced. After three weeks, 14 of 23 otters settled within their release areas, while two died and seven moved away from release areas. Three years after the first translocations, five female otters had successfully reproduced, producing nine young. At this time, the total population was 12 otters. In 2002, fifteen wild-caught otters were released at one site. At a second site, in 2004–2005, eight animals, comprising a mix of wild-caught and captive-bred individuals, were released. Before release, animals were fitted with radio-transmitters and DNA samples were taken. Following release, otters were monitored by radio-tracking and by collection of faeces, which was analysed to identify individuals.Study and other actions tested
A study in 1998–2005 at a prairie grassland site in Montana, USA (Ausband & Foresman 2007) found that following releases of captive-reared swift foxes Vulpes velox, a population became established and grew. One year after releases finished, there were 62 animals, increasing to 93 animals two years later. From 50 to 100% of mature female swift foxes reproduced each year, producing 4–5 offspring. Five to seven years after reintroductions, adult swift fox annual survival was 60–73%, and that of young swift foxes was 69–77%. Of the 33 animals that died during the study, 26 were killed by coyotes Canis latrans or birds of prey. In 1998–2002, one-hundred and twenty-three captive-reared swift foxes were released in the Blackfeet Indian Reservation. In 2003–2005, twenty-three adult and 35 juvenile foxes were trapped and radio-collared. They were then tracked weekly, until 2005.Study and other actions tested
A review of studies conducted in 1985–2005 at 11 grassland and dry savanna sites in Eastern Cape, South Africa (Hayward et al. 2007) found that reintroductions (mainly through translocations but including some captive-bred animals) of large carnivores led to increasing population sizes for four of six species. Twenty years after the first releases, there were 56 lions Pantera leo at seven sites (from 31 released), 41 cheetahs Acinonyx jubatu (seven sites, 40 released), 24 African wild dogs Lycaon pictus (two sites, 11 released) and 13 spotted hyena Crocuta crocuta (three sites, 11 released). There were reductions or unknown trends in two species with seven known surviving leopards Panthera pardus (five sites, 15 released) and an unknown number of servals Leptailurus serval (though known to be present - two sites, 16 released). Releases were made in 1985–2005, into 11 protected areas. Most schemes involved translocations of wild-caught animals but at least one of seven lion reintroductions involved captive-bred animals. Monitoring methods are not specified.Study and other actions tested
A replicated study in 1998–2004 of woodland at three sites in Corsica, France (Kidjo et al. 2007) found that captive-bred Corsican red deer Cervus elaphus corsicanus, released following extinction on the island, increased in number at all three sites. At one site, following two releases, four years apart, totalling 35 founders, there were 100 deer two years after the second release. At a second site, 24 founders grew to 60 animals over seven years. Twenty-seven founders released at a third site increased to 40 animals later that year. Corsican red deer became extinct on Corsica in 1970. Captive populations of deer, sourced from Sardinia, were established at three sites on Corsica from 1985 onwards, to provide animals for reintroductions. From 7, 14 and 17 founders, captive populations in enclosures grew and were artificially restricted to 35 each at two sites and 50 at the third site (each equating to 3.2 deer/ha). Releases from the captive populations took place in February and March of 1998–2004 and the wild population was then estimated at each site later in 2004.Study and other actions tested
A review in 2008 of 49 studies in 1990–2006 of carnivore reintroductions in Africa, Europe, and North America (Jule et al. 2008) found that captive-bred animals released into the wild had lower survival than did wild-born translocated animals. Survival of captive-born carnivores following release (32%) was lower than survival of wild-born translocated animals (53%). The review analysed 20 reintroductions of 983 captive-bred carnivores and 29 reintroductions of 1,169 wild-caught carnivores. Post-release monitoring ranged in duration from 6 to 18 months.Study and other actions tested
A replicated study in 2003–2007 at two mountain sites on Vancouver Island, Canada (Aaltonen et al. 2009) found that released captive-born Vancouver Island marmots Marmota vancouverensis had lower annual survival rates than wild-born marmots, and those released at two years old were more likely to survive than those released as yearlings. The average annual post-release survival rate of captive-bred marmots (61%) was lower than that of wild-born marmots (85%). Captive-bred marmots released at the age of two or more years had higher annual survival rates (77%) than those released as yearlings (60%). In 2003–2007, ninety-six captive-born Vancouver Island marmots were released at two sites. The released marmots were radio-tagged and monitored for a total of 154 marmot-years (one marmot-year represents one record/marmot/year). Wild-born marmots (number not reported) were also radio-tagged and monitored for 101 marmot-years in 2003–2007. All radio-tagged marmots were tracked from the ground or from a helicopter. Monitoring frequency is not stated.Study and other actions tested
A study in 2004–2006 at a grassland reserve in KwaZulu-Natal, South Africa (Grey-Ross et al. 2009) found that one of 10 captive-bred oribi Ourebia ourebi released into the wild survived more than two years. One captive-bred female oribi released into the wild survived for at least 27 months. Eight oribi died, six within one month of release and three within eight months. One oribi was taken back into captivity with a broken leg. Two of the eight animals that died were predated, two were poached, one died in cold weather and the cause of death in three cases was unknown. In April 2004, ten adult oribi (four males, six females) from a private breeding facility (9 x 1–3 ha enclosures) were fitted with radio-collars and released into two grassland sites (five animals at each) within three hours of capture. In 2004–2005, the released oribi were monitored weekly during the first month and monthly after the first three months post-release.Study and other actions tested
A study in 2000–2006 in an unspecified number of riparian sites on Hiiumaa Island, Estonia (Maran et al. 2009) found that captive-bred European mink Mustela lutreola survived up to 39 months after release into the wild. Eighty days after release, 88 of 172 released mink had survived. After 39 months, at least one released mink was still alive. Seventy-five percent of deaths were caused by predators, including foxes, dogs Canis lupus familiaris, and raptors. In autumn 2000–2003, one-hundred and seventy-two captive-born mink were released at the site. Fifty-four mink were fitted with radio-collars before release and were monitored for up to five months. To monitor mink survival, animals were repeatedly trapped over 39 months.Study and other actions tested
A study in 2008 along a river in northern Italy (Prigioni et al. 2009) found that the release of a pair of captive-bred Eurasian otters Lutra lutra resulted in a population that persisted for at least 11 years. Eleven years after the introduction of a pair of Eurasian otters, signs of otter presence were detected along at least three of the 10 contiguous stretches of river that were surveyed. In 1997, a pair of captive-bred otters was released at a site in an area where the species had been extirpated in the late 1980s. In June–September 2008, otter presence was monitored along 5 km of the river, in 10 stretches, each 500 m long. Monitoring entailed searches for spraints and anal secretions. Each river stretch was surveyed 8–11 times.Study and other actions tested
A study in 2002–2008 in an area of peatland, fen, woodland, ditches and lakes in the Netherlands (Koelewijn et al. 2010) found that following release of captive-bred and translocated wild-born Eurasian otters Lutra lutra, the population grew. By the end of the study (1–6 years after releases), six of the released otters were known to be still alive. Fifty-four offspring from released otters or their descendants were detected during the course of the study. Most dead otters found were killed in collisions with road vehicles. Between July 2002 and November 2007, thirty otters were released. Thirteen were captive-bred and 17 were translocated, wild-caught animals. Monitoring was mostly by genetic analysis of otter spraints. A publicity campaign encouraged people to report dead otters that they found. These were examined to establish cause of death.Study and other actions tested
Referenced paperKoelewijn H., Perez-Haro M., Jansman H.A.H., Boerwinkel M.C., Bovenschen J., Lammertsma D.R., Niewold F.J.J. & Kuiters A.T. (2010) The reintroduction of the Eurasian otter (Lutra lutra) into the Netherlands: hidden life revealed by noninvasive genetic monitoring. Conservation Genetics, 11, 601-614.
A review of studies in 1991–2008 at 11 grassland sites in the USA and Mexico (Jachowski et al. 2011) found that most captive-bred (with some translocated) black-footed ferret Mustela nigripes releases were unsuccessful at maintaining a population, but success was higher where prey was abundant over larger areas. Of 11 reintroduction sites, populations of more than 30 adult black-footed ferrets were maintained at four sites over two years without further reintroductions. Two sites no longer contained ferrets by December 2008, and the other five sites only had small populations or were supplemented by further releases. Sites where populations were maintained tended to have more prairie dogs Cynomys spp., the main prey species of black-footed ferrets, covering a larger area (at least 4,300 ha) and with a higher density of animals (data presented as index of prairie dog abundance). From 1991–2008, around 2,964 captive-bred and 157 translocated wild ferrets were released at 18 sites in multiple releases. The study reports success of the 11 sites where initial releases occurred before 2003. Sites received on average over 200 ferrets over 10 years. Ferrets were monitored by annual spotlight surveys to locate, capture and uniquely mark individuals.Study and other actions tested
A study in 2009–2010 of a woodland area and adjacent escarpment in Victoria, Australia (Molyneux et al. 2011) found that most captive-bred brush-tailed rock-wallabies Petrogale penicillata survived for at least five months after release and established stable home ranges. Four animals from five released were alive at least five months after release. One animal died two months after release, from undetermined causes. Additionally, three animals from an earlier release that were alive 11 months after release all survived to at least 16 months after release. Rock-wallabies established stable home ranges of 16.2–41.5 ha in extent, with core areas of 1.2–4.5 ha. Five captive-bred brush-tailed rock-wallabies were released in October 2009. Three from a release in November 2008 that were still alive in October 2009 were also monitored. Wallabies were monitored by radio-tracking, through October 2009 and for two weeks in March 2010.Study and other actions tested
A replicated study in 1996–1997 in three grassland sites in South Dakota, USA (Poessel et al. 2011) found that over half of released captive-bred black-footed ferrets Mustela nigripes survived more than two weeks. At each of the three sites, 48% (12 of 25), 50% (9 of 18) and 89% (32 of 36) of captive-bred ferrets released into the wild survived for at least two weeks (long term survival is not reported). Overall, 53 out of 79 captive-bred black-footed ferrets (67%) survived more than two weeks after release into the wild. Twenty-four ferrets were killed by native predators (mostly great-horned owls Bubo virginianus and coyotes Canis latrans) and the cause of death of two others could not be determined. A total of 79 captive-bred black-footed ferrets were released across three mixed-grass prairie sites (18–36 ferrets/site) in September–October 1996 and October–November 1997. Between 18 and 35 individuals were released at each site. Each of the 79 ferrets was radio-tagged and tracked every 5–30 min/night for two weeks post-release in 1996–1997.Study and other actions tested
A study in 1990–2007 in a desert reserve in west-central Saudi Arabia (Wronski et al. 2011) found that released captive-bred female Arabian oryx Oryx leucoryx survived more than 10 years and successfully reproduced, regardless of prior breeding experience. Released captive-bred female oryx lived 11-12 years in the wild. Average birth rates were similar for ’experienced’ females that had given birth prior to release (0.69 calves/year) and ‘inexperienced’ females that had not (0.74 calves/year). Between 1990 and 1994, a total of 76 captive-bred oryx were released, of which 36 were females aged 0.5-8.9 years (numbers of experienced/inexperienced mothers not specified). Animals were identified by collars, ear-tags or ear notches. Individuals were located at least once every two weeks until 2007.Study and other actions tested
A study in 2005–2009 in a mostly agricultural area in Maciejowice, Poland (Misiorowska & Wasilewski 2012) found that approximately one third of released captive-bred brown hares Lepus europaeus survived for at least one year. Twenty-two of 60 hares (37%) survived for at least one year after release. Of those that died during the first year after release, males survived for an average of 57 days and females for an average of 64 days. Deaths were due to predation (31%), poaching (13%) and road kills (7%), with the remainder (49%) disappearing or dying of unknown causes. Seventy-eight brown hares bred in a 20-ha open-field enclosure were released in a landscape comprising cultivated fields, floodbanks, forest, orchards and meadows. The hares (at least six months old) were released in groups of 18–30 individuals in November 2005, 2006 and 2007. Sixty radio-collared hares (15–29 hares/group) were tracked 3–7 times/week for 1–2 years after release in 2005–2009.Study and other actions tested
A study in 2002–2011 of forest on two islands in Florida, USA (McCleery et al. 2013) found that released captive-bred Key Largo woodrats Neotoma floridana smalli had a lower survival rate than did wild-born, wild-living animals. From 40 captive-bred woodrats radio-tracked for an average of 49 days, 33 (67%) deaths were recorded. From 58 wild-born, wild-living woodrats radio-tracked for an average of 80 days, ten (6%) deaths were recorded. All but one death, from both groups combined, was thought to be due to predation. Adult captive-bred woodrats were released on two islands between February 2010 and December 2011. They were located at least every second day by radio-tracking, for up to four months. Nineteen adult wild-born woodrats were radio-tracked at least three times/week from March to December 2002 and 39 were radio-tracked 2–5 times/week, from June 2005 to February 2006.Study and other actions tested
Referenced paperMcCleery R., Oli M.K., Hostetler J.A., Karmacharya B., Greene D., Winchester C., Gore J., Sneckenberger S., Castleberry S.B. & Mengak M.T. (2013) Are declines of an endangered mammal predation-driven, and can a captive-breeding and release program aid their recovery? Journal of Zoology, 291, 59-68.
A review of translocations carried out in 1969–2006 in Australia (Clayton et al. 2014) found that releasing captive-bred and wild-born translocated macropod species (kangaroos and allies) led to the successful establishment of populations in 44 of 72 cases, of which 29 survived for over five years. Of the established populations, 29 persisted for more than five years. Of the 28 releases considered to be failures, 17 were thought to have failed due to predation by non-native carnivores, such as red foxes Vulpes vulpes. Releases considered in the review included both wild-caught translocated animals and captive-bred animals. The number of animals released ranged from one to 70 and included 20 different macropod species. Only translocations where animals were released into areas larger than 100 ha were considered for the review.Study and other actions tested
A study in 2002–2007 on prairie in South Dakota, USA (Sasmal et al. 2015) found that post-release survival rates of captive-bred swift fox Vulpes velox pups were lower than survival rates of wild-born pups. The proportion of captive-bred pups that survived for 60 days after release (48%) was lower than the proportion of wild-born pups that survived for 60 days (100%). Forty-three pups (26 male, 17 female) born in pens to wild-caught foxes formed the captive-bred cohort. They were released in mid-July of 2003–2007. Survival was compared, using radio-telemetry and visual observations at dens, to that of 90 pups born in the wild in 2003–2007, to previously translocated and released foxes.Study and other actions tested
A controlled study in 2008–2010 in a mountain site in the Central Apennines, Italy (Bocci et al. 2016) found that released captive-born Apennine chamois Rupicapra pyrenaica ornata survived and reproduced in similar numbers to wild-caught translocated chamois, but captive-born chamois remained closer to the release site. Seven of eight captive-born (88%) and seven of eight (88%) wild-caught translocated Apennine chamois survived over five months after release. Four of five captive-born (80%) and three of five wild-caught translocated (60%) female chamois reproduced in the first year after release. During the first week after release, captive-born chamois remained closer to the release site (within 1.1 km on average) than wild-caught chamois (average 1.8 km). Eight captive-born chamois (2.5–11.5 years old, five females and three males) and eight wild-caught translocated chamois (2.5–10.5 years old, five females and three males) were released into Sibillini Mountains National Park. Chamois were released in groups of one-three individuals; each group was all wild or all captive-born. Captive-born chamois were bred in large enclosures within four national parks. Translocated chamois were taken from a national park approximately 200 km away. All of the 16 released chamois were fitted with radio-collars and monitored for five months after release in 2008–2010.Study and other actions tested
A study in 1997–2016 in a grassland area in Jiangsu province, China (Yuan et al. 2017) found that a population of released captive-bred Père David's deer Elaphurus davidianus, established and increased in number over time. From a total of 82 founders, the population increased to 325 animals by 18 years after the first of these founders were released. In 1998, seven deer were released into a 1,000-ha area in which there were no other Père David's deer. Between 2002 and 2016, a further 75 animals were released. Observations were made with binoculars and using a drone, to estimate the deer population size. No other details of monitoring were provided in the study.Study and other actions tested
Referenced paperYuan B.D., Wang L.B., Xie S.B., Ren Y.J., Liu B., Jia Y.Y., Shen H., Sun D.M. & Ruan H.H. (2017) Density dependence effects on demographic parameters - a case study of Père David's deer (Elaphurus davidianus) in captive and wild habitats. Biology and Environment: Proceedings of the Royal Irish Academy, 117, 139-144.