Release translocated/captive-bred mammals to areas outside historical range
Overall effectiveness category Likely to be beneficial
Number of studies: 7
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Background information and definitions
Endangered species are sometimes translocated from other areas or bred in captivity for release into their former range. Sometimes, though, the former range remains unsuitable for the species, for example through presence of an invasive predator. In such cases, releases to sites outside the former range may be considered, if these potentially offer better conditions for persistence of the species.
Supporting evidence from individual studies
A study in 1970–1978 in a grassland and forest reserve in southeast Kenya (Sekulic 1978) found that after release of translocated roan Hippotragus equinus into an area outside their native range, the population persisted and bred for more than six years. Only eight out of the original 38 translocated roan could be located 18 months years after the last release. However, six years after the last translocations, roan numbers had increased to 22. From 1973–1976, at least 15 calves were born, of which one-third survived to nine months of age. Between 1970 and 1972, 38 roan were released in Shimba Hills National Reserve, where there is no evidence for their existence since at least 1885. Animals were captured in the Ithanga Hills, by funnelling them into a 2.5 acre corral using horses, trucks and a helicopter. Prior to release roan were kept in a 30-acre holding pen. Roan were monitored between June 1973 and January 1978, but no further monitoring details are provided.Study and other actions tested
A study in 1996–1999 in a woodland reserve in Queensland, Australia (Pople et al. 2001) found that translocated, captive-bred and enclosure born bridled nailtail wallabies Onychogalea fraenata released into areas outside their historical range had annual survival rates of 40–88% and the population increased three-fold over four years. The average annual survival of bridled nailtail wallabies varied by release group between 40 and 88%. During four years, in which 133 wallabies were released, the population increased to approximately 400 individuals. In 1996–1997, nine wild-born translocated and 39 captive-bred bridled nailtail wallabies were released in three sites across Idalia National Park. In 1997–1998, eighty-five wallabies born (from captive animals) within a 10 ha enclosure on the reserve were also released. All released wallabies were kept in a holding pen (30 m diameter) for a week at each site before release. Mammalian predators were culled at release sites. Wallabies were individually marked with ear tags. A total of 37 wallabies (9 wild-born translocated, 28 captive-bred) were radio-tagged and tracked every 2–7 days in 1996–1998. Wallabies were live-trapped at irregular intervals with 20–35 wire cage traps in 1997–1999. Vehicle spotlight surveys were carried out 3–4 times/year in 1996–1999.Study and other actions tested
A study in 1980–2007 in a mountain grassland site in the Mézenc Massif, France (Ramousse et al. 2009) found that after the release of translocated Alpine marmots Marmota marmota into a site outside their historical range, numbers increased more than four-fold over 27 years. Twenty-seven years after the onset of the translocation, marmot numbers had increased to 492, from the 108 originally released. Population growth fluctuated over time with some population declines in 1990, 1993, 1997 and 2001 (see original paper for details). In 1980, eleven marmots were translocated into a mountain area outside their historical range. This was followed by seven reinforcements (translocation dates not provided), with a total of 108 translocated individuals by 2001. Marmots were monitored discontinuously until 1988, and then annually (five times through spring to autumn). Monitoring details are not provided.Study and other actions tested
A study in 1949-2001 in South Africa (Van Houtan et al. 2009) found that following translocations outside of the species’ native ranges, population sizes of most of 22 species of herbivorous mammals increased. Following translocation, 82 out of 125 populations (66%) of 22 species of mammals (white rhinoceros Ceratotherium simum, mountain zebra Equus zebra, plains zebra Equus quagga, giraffe Giraffa camelopardalis, African buffalo Syncerus caffer and 17 species of antelope) had positive growth rates (data presented as results of population growth models). Seventeen of the 22 species were introduced outside of their historical range. Population models were based on long-term monitoring data from 178 populations relocated to 24 reserves in 1949-1978 (see original paper for modelling details). Only translocations with five or more consecutive years of monitoring results were included (125 translocations, monitoring data duration: 5-47 years). Translocation details are not provided but authors state that most translocated populations began with fewer than 15 individuals and that most reserves contained water impoundments and lacked top predators, such as lions Panthera leo or spotted hyenas Crocuta crocuta.Study and other actions tested
A review of studies in 1948–2003 in nine mountain grassland sites in the Pyrenees in Andorra, Spain and France (Barrio et al. 2013) found that following translocation to areas outside their native range, alpine marmots Marmota marmota had similar densities and family group sizes to those of populations in their native range. Average marmot densities and family group sizes did not differ significantly between translocated populations (0.9 individuals/ha; 5 individuals/group) and populations within their native range (1.4 individuals/ha; 6 individuals/group). Between 1948 and 1988, around 500 alpine marmots were translocated to multiple sites across the Pyrenees in areas outside their native range. In 1965–2003, nine marmot populations (comprising 2–14 family groups) were monitored for 1–2 years in the introduced range and 11 populations (3–50 family groups) were monitored for 1–13 years in their native range (French, German, Italian and Swiss Alps). Monitoring methods are not provided.Study and other actions tested
A study in 2012–2013 on an offshore island in Tasmania, Australia (Thalmann et al. 2016) found that most captive-bred Tasmanian devils Sarcophilus harrisii released into an area outside their native range survived over four months after release. Fourteen out of 15 captive-bred Tasmanian devils survived >4 months (122 days) after release. In November 2012, fifteen captive-bred Tasmanian devils were released onto a 9,650-ha island reserve, 12 km off the Tasmanian mainland. Seven individuals were from a captive breeding facility, where animals were raised in groups of 1–4 in 1-ha pens. Eight were from a captive breeding facility were animals were raised in groups of 20–25 in 22-ha enclosures. Animals that shared pens in captivity were released together. Supplementary wallaby meat (20 kg) was provided at two-week intervals. Tasmanian devils were monitored for 122 days through video footage obtained at feeding sites. Individuals were identified by unique markings and scars.Study and other actions tested
A study in 2012–2013 on an island with mixed forest and grassland vegetation in Victoria, Australia (Groenewegen et al. 2017) found that, following releases of captive-bred and wild-caught translocated eastern barred bandicoots Perameles gunnii to a red fox Vulpes vulpes-free island outside of the species’ historical range, half of animals survived for at least two months. Nine out of 18 released bandicoots were still alive two months after release while seven survived at least 100 days. Deaths included two to cat predation and two to disease (toxoplasmosis). Between July and September 2012, eighteen eastern barred bandicoots were released on a fox-free island outside of the historical range of the species with 9,000 ha of potentially suitable habitat. Four animals were captive-bred and 14 animals were translocated from a reintroduction site on the mainland. All were fitted with radio-transmitters and PIT-tags to allow tracking and identification of individuals. Each bandicoot was radio-tracked from the day after its release until November 2012.Study and other actions tested
Where has this evidence come from?
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This Action forms part of the Action Synopsis:Terrestrial Mammal Conservation
Terrestrial Mammal Conservation - Published 2020
Terrestrial Mammal Conservation