Estimating the abundance of the bilby (Macrotis lagotis): a vulnerable, uncommon, nocturnal marsupial

The high failure rate of threatened species translocations has prompted many managers to fence areas to protect wildlife from introduced predators. However, conservation fencing is expensive, restrictive and exacerbates prey na€ ıvet e reducing the chance of future co-existence between native prey and introduced predators. Here, we ask whether two globally threatened mammal species protected in fenced reserves, with a history of predation-driven decline and reintroduction failure, could co-exist with introduced predators. We defined coexistence as population persistence for at least 3 years and successful recruitment. We manipulated the density of feral cats within a large fenced paddock and measured the impact on abundance and reproduction of 353 reintroduced burrowing bettongs and 47 greater bilbies over 3 years. We increased cat densities from 0.038 to 0.46 per square km and both threatened species survived, reproduced and increased their population size. However, a previous reintroduction trial of 66 bettongs into the same paddock found one red fox (Vulpes vulpes), at a density of 0.027 per square km, drove the bettong population extinct within 12 months. Our results show that different predator species vary in their impact and that despite a history of reintroduction failure, threatened mammal species can co-exist with low densities of feral cats. There may be a threshold density below which it is possible to maintain unfenced populations of reintroduced marsupials. Understanding the numerical relationships between population densities of introduced predators and threatened species is urgently needed if these species are to be re-established at landscape scales. Such knowledge will enable a priori assessment of the risk of reintroduction failure thereby increasing the likelihood of reintroduction success and reducing the financial and ethical cost of failed translocations.

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“…), and bilbies reintroduced to the Currawinya fenced reserve in Queensland were decimated by cat incursions (Lollback et al . ).…”

Section: Methodsmentioning

confidence: 97%

Understanding predator densities for successful co‐existence of alien predators and threatened prey

et al. 2018

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“…As the bilby continues to decline in the wild, the conservation of this species is increasingly dependent on the maintenance of genetically and demographically viable populations held behind predator‐proof fences (Pavey , Southgate et al , Lollback et al , Legge et al ). In this study, we characterized the genetic diversity, gene flow, and population structure of bilbies from captive and conservation‐fenced sites across Australia.…”

Section: Discussionmentioning

confidence: 99%

“…Despite this, bilby populations have declined over the past 150 years because of habitat loss, competition with introduced herbivores, and predation by exotic carnivores (Woinarski et al ). The species is now largely restricted to regions of low‐productivity, where it naturally occurs at low population densities (Southgate et al , Lollback et al ). A National Recovery Plan, which includes a captive breeding and translocation program, has been developed and implemented with the stated goal of retaining ≥90% of current genetic variation for 100 years (Pavey ).…”

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confidence: 99%

Genetic Management of Captive and Reintroduced Bilby Populations

et al. 2019

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Captive breeding and translocation, whereby selected individuals are used to supplement or re‐establish failing populations, are powerful tools for conserving threatened fauna. These tools, however, are rarely successful at establishing self‐sustaining populations that can survive without ongoing human assistance. The maintenance of genetic diversity and demographic security in captivity, or following wildlife translocation events, is important for improving the long‐term effectiveness of threatened species recovery efforts around the world. Routine population monitoring using hypervariable genetic markers represents a promising technique for evaluating the effect of established management practices on population structure and genetic diversity across various spatial and temporal scales. In this study, we employed a data set of 1,068 single nucleotide polymorphisms to conduct a comprehensive survey of population structure and genetic diversity in greater bilbies (Macrotis lagotis) held at 13 zoos and wildlife sanctuaries across Australia between August 1996 and December 2016. We observed significant genetic structuring across the study sites, consistent with the limited exchange of animals between independently managed facilities. The majority of variation, however, still occurred at the level of individual bilbies (75%, P < 0.001). We also uncovered evidence for an ongoing loss of genetic diversity in some conservation‐fenced populations, despite a slight excess of heterozygosity across the sampling sites as a whole. Maintaining the genetic health of bilbies in captivity or following translocation will therefore require stakeholders to focus on reducing individual mortality, and maintaining genetic connectivity across all existing populations through the regular exchange of selected individuals. As such, admixture is expected to play an increasingly important role in future conservation programs. © 2019 The Authors. Journal of Wildlife Management published by Wiley Periodicals, Inc. on behalf of The Wildlife Society.

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“…For example, the iconic greater bilby ( Macrotis lagotis ), once inhabited most of arid and semi‐arid Australia, but due to predation by introduced predators and other factors, is now severely restricted in both range and abundance (Southgate, 1990). Predation by feral cats and foxes has resulted in unsuccessful reintroduction attempts of this species in South Australia, and population crashes in a fenced reserve when cats breached the fence in Queensland (Moseby et al ., 2011; Lollback et al ., 2015).…”

Section: Introductionmentioning

confidence: 99%

Relaxed predation theory: size, sex and brains matter

et al. 2020

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Australia's wildlife is being considerably impacted by introduced mammalian predators such as cats (Felis catus), dogs (Canis lupus familiaris), and foxes (Vulpes vulpes). This is often attributed to native wildlife being naïve to these introduced predators. A systematic review of the literature reveals that native metatherians (body mass range 0.02–25 kg) do not recognise, and show relaxed antipredator behaviours towards, native and some introduced mammalian predators. Native eutherians (all with body mass < 2 kg), however, do appear to recognise and exhibit antipredator behaviours towards both native and introduced predators. Based on our findings, we propose a novel theory, the ‘Relaxed Predation Theory’. Our new theory is based on the absence of large mammalian predators leading to reduced predation pressure in Australia during the past 40000–50000 years, and on three key differences between Australian metatherians and eutherians: size, sex, and brains. In light of this Relaxed Predation Theory, we make a number of recommendations for the conservation of Australian wildlife: (i) predator avoidance training of suitable species; (ii) exclusion fencing to exclude some, but not all, predators to facilitate the development of antipredator behaviours; (iii) captive breeding programs to prevent the extinction of some species; and (iv) reintroduction of Australia's larger predators, potentially to compete with and displace introduced predators. A more detailed understanding of the responses of Australian mammals to predators will hopefully contribute to the improved conservation of susceptible species.

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Estimating the abundance of the bilby (Macrotis lagotis): a vulnerable, uncommon, nocturnal marsupial

Cited by 13 publications

References 56 publications

Understanding predator densities for successful co‐existence of alien predators and threatened prey

Understanding predator densities for successful co‐existence of alien predators and threatened prey

Genetic Management of Captive and Reintroduced Bilby Populations

Relaxed predation theory: size, sex and brains matter

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