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Providing evidence to improve practice

Action: Release translocated/captive-bred mammals to islands without invasive predators Terrestrial Mammal Conservation

Key messages

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  • Six studies evaluated the effects of releasing translocated or captive-bred mammals to islands without invasive predators. The six studies were in Australia.

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (7 STUDIES)

  • Abundance (2 studies): A study in Australia found that following release of captive-bred dibblers on to an island free of introduced predators, numbers increased. A replicated study in Australia found that following release of captive-bred and wild-born brush-tailed bettong onto islands free of foxes or cats, numbers increased on two of four islands.
  • Reproductive success (3 studies): A study in Australia found that captive-bred proserpine rock-wallabies released on an island without introduced predators established a breeding population. Two studies in Australia found that following release on to islands without invasive predators, captive-bred rufous hare-wallabies and captive-bred dibblers.
  • Survival (3 studies): A review of 28 translocation studies in Australia found that 67% of marsupial populations translocated to islands without predators survived more than five years, compared to 0% translocated to islands with predators and 20% translocated to the mainland. A study in Australia found that most captive-bred rufous hare-wallabies released on an island without non-native predators survived more than a year. A replicated study in Australia found that wild-born golden bandicoots descended from translocated populations released onto two predator-free islands persisted for 2–3 years.
  • Condition (1 study): A replicated study in Australia found that wild-born golden bandicoots descended from translocated populations that had been released onto two predator-free islands, maintained genetic diversity relative to founder and source populations.

BEHAVIOUR (0 STUDIES)

Supporting evidence from individual studies

1 

A replicated study in 1979–1984 of shrubland and grassland on five islands in South Australia, Australia (Delroy  et al. 1986) found that captive-bred and wild-born brush-tailed bettong Bettongia penicillata populations released onto islands free of foxes Vulpes vulpes, rabbits Oryctolagus cuniculus or cats Felis catus increased in number on two of the four islands on which they were released and monitored. On one island, seven founders increased to ≥53 animals in four years. On a second island, 10 founders increased to 12 animals (five born on the island), 14 months later. Forty released on a third island declined to one after two years. Six released on a fourth island were predated by dogs Canis lupus familiaris after an unspecified period. On a fifth island, where 11 were released, animals persisted for up to 12 months, but were not formally monitored. Releases were of captive-bred animals, except those on the second island, which were wild-bred offspring from the population established on the first island. Releases were made in 1979–1983 and were monitored, primarily by live-trapping, up to April 1984. The results of this study are also included in (Short et al. 1992).

2 

A review of 28 translocation studies in 1905-1990 on islands and mainland Australia (Short et al. 1992) found that eight of 12 marsupial populations translocated to islands without predators survived more than five years, none of six populations translocated to islands with predators survived and two of 10 translocations to the mainland survived more than five years. One of 12 populations of marsupials translocated to islands with no predators recorded survived at least 1-5 years, four survived 6-20 years and four survived >20 years (outcome of three translocations unknown). Five of six populations of marsupials translocated to islands with predators survived <1 year and one population survived 1-5 years. Three of 10 populations of marsupials translocated to the mainland survived <1 year, four survived 1-5 years and two survived 6-20 years (outcome of 1 translocation unknown). Translocations took place in 1905-1988 and included: banded hare-wallaby Lagostrophus fasciatus, black-flanked rock-wallaby Petrogale lateralis, bridled nail-tail wallaby Onychogalea fraenata, brush-tailed bettong (‘woylie’) Bettongia penicillata, brush-tailed rock-wallaby Petrogale penicillata, burrowing wallaby Bettongia lesueur, parma wallaby Macropus parma, quokka Setonix brachyurus, red-bellied pademelon Thylogale billardierii, rufous hare-wallaby Lagorchestes hirsutus, tammar wallaby Macropus eugenii, and western grey kangaroo Macropus fuliginosus. Predators were recorded as limiting factors in six island studies and were controlled in two mainland studies. Numbers of translocated animals ranged from 4-113, except for quokkas, of which 673 were translocated (see original paper for details).

3 

A study in 1998–2001 on an offshore island dominated by grassland in Western Australia, Australia (Langford & Burbidge 2001) found that following release on an island without non-native predators, most captive-bred rufous hare-wallabies (‘mala’) Lagorchestes hirsutus survived over one year after release and some reproduced. Twenty-four (80%) of 30 rufous hare-wallabies survived at least one year after release. Rufous hare-wallabies were still present on the island three years post-release and animals had reproduced in the wild. In June 1998, thirty captive-bred rufous hare-wallabies from a captive colony were released on to a 520-ha predator-free island, part of the Montebello Islands Conservation Park. Animals were transported in 5 × 3 m holding pens and were ear-tagged and fitted with a radio-collar before release. Hare-wallabies were released within 20 hours of capture and fruit, alfalfa and water were made available to them immediately after release. They were monitored every two days for 10 days and intermittently for up to three years post-release.

4 

A study in 1998–2002 on an offshore island in Queensland, Australia (Johnson et al. 2003) found that captive-bred proserpine rock-wallabies Petrogale persephone released on an island without introduced predators established a breeding population. No statistical tests were carried out and no data on population size are provided. Four rock-wallabies were born on the island, 3–4 years after the translocation of 27 animals commenced. However, nine rock-wallaby deaths were recorded over the study period (33% of all animals released). Between 1998 and 2002, twenty-seven rock-wallabies were translocated from the Queensland mainland to Hayman Island. Feral goats Capra hircus were eradicated before the release. Released individuals were radio-tracked over three-day periods at three-week intervals in 1998–1999, over one day every month in 2000 and over one day every two months in 2001. Remote video surveillance was used occasionally in 2001 to confirm breeding.

5 

A study in 1998–2001 on an offshore predator-free island dominated by shrubland in Western Australia, Australia (Moro 2003) found that following release on to an island free of introduced predators and rodents, captive-bred dibblers Parantechinus apicalis reproduced and numbers increased. Three years after the first release, more dibblers were confirmed to be alive on the island (67 animals) than in the first year of releases (26 animals). After three years, the proportion of females showing signs of recent reproduction (90%) was higher than after one year (20%). Of animals released in the first year, 10 of 26 survived for at least 12 months. Between 1998 and 2000, eighty-eight captive-bred dibbers were released on an 11-ha offshore island, free of introduced predators and rodents. All dibblers were individually marked and one-third was fitted with radio-collars. Twenty-five dibblers were radio-tracked for two weeks. For three to four nights, on 10 occasions from November 1998 to October 2001, up to 100 live traps were set across the island. New animals caught were marked to enable individual identification and females were examined for signs of recent breeding.

6 

A replicated study in 2010–2013 on two islands in Western Australia, Australia (Ottewell et al. 2014) found that wild-born golden bandicoots Isoodon auratus, descended from translocated populations which had been released onto two predator-free islands, maintained genetic diversity relative to founder and source populations and persisted for 2–3 years. For four measures of genetic diversity (allelic richness, the number of effective alleles/locus, observed heterozygosity and expected heterozygosity) there were no significant differences between descendants from translocated animals, founder animals that were translocated or source populations (see paper for details). On the larger island, the population size was estimated to be 280 animals in 2013. No estimate is provided for the smaller island. Bandicoots were trapped on Barrow Island, which has a large population, in February 2010 (165 animals) and July 2011 (92 animals). Within 24 h of capture they were released on two other islands (1,020 and 261 ha) where non-native predators had been eradicated or had never been recorded. Genetic material was sampled by ear punch biopsy from 38 and 49 founders in 2010 and 2011, and from 44 and 39 wild-born offspring in 2010–2012.

Referenced papers

Please cite as:

Littlewood, N.A., Rocha, R., Smith, R.K., Martin, P.A., Lockhart, S.L., Schoonover, R.F., Wilman, E., Bladon, A.J., Sainsbury, K.A., Pimm S. and Sutherland, W.J. (2020) Terrestrial Mammal Conservation: Global Evidence for the Effects of Interventions for terrestrial mammals excluding bats and primates. Synopses of Conservation Evidence Series. University of Cambridge, Cambridge, UK.