Mini Safe Havens for population recovery and reintroductions 'beyond-the-fence'

In response to the ongoing decline of fauna worldwide, there has been growing interest in the rewilding of whole ecosystems outside of fenced sanctuaries or offshore islands. This interest will inevitably result in attempts to restore species where eliminating threats from predators and competitors is extremely challenging or impossible, or reintroductions of predators that will increase predation risk for extant prey (i.e., coexistence conservation). We propose 'Mini Safe Havens' (MSHs) as a potential tool for managing these threats. Mini Safe Havens are refuges that are permanently permeable to the focal species; allowing the emigration of individuals while maintaining gene flow through the boundary. Crucial to the effectiveness of the approach is the ongoing maintenance and monitoring required to preserve a low-to-zero risk of key threats within the MSH; facilitating in-situ learning and adaptation by focal species to these threats, at a rate and intensity of exposure determined by the animals themselves. We trialled the MSH approach for a pilot reintroduction of the Australian native New Holland mouse (Pseudomys novaehollandiae), in the context of a trophic rewilding project to address potential naïveté to a reintroduced native mammalian predator. We found that mice released into a MSH maintained their weight and continued to use the release site beyond 17 months (525 days) post-release. In contrast, individuals in temporary soft-release enclosures tended to lose weight and became undetectable approximately 1-month post-release. We discuss the broad applicability of MSHs for population recovery and reintroductions 'beyond-the-fence' and recommend avenues for further refinement of the approach.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10531-022-02495-6.

Prey selectivity by feral cats at central Australian rock-wallaby colonies

Threatened warru, or black-footed rock-wallaby (Petrogale lateralis MacDonnell Ranges race), populations in northern South Australia continued to decline despite baiting for foxes (Vulpes vulpes), which improved their short-term conservation status elsewhere. To investigate whether feral cats (Felis catus) also represent a risk to warru we compared frequencies of prey occurrence in 103 feral cat and 14 fox stomachs shot near warru colonies in northern South Australia during 2001–17 with measures of prey abundance from pitfall trapping and opportunistic searches. We hypothesise that one fresh adult warru kill and the presence of warru remains in four other cats suggests predation by cats on adult and juvenile warru. Small reptiles and invertebrates were the most frequently recorded prey of cats in summer, whereas rodents and small dasyurids were the most frequent prey items in winter. Small mammals, small snakes and pygopodid lizards were over-represented in the diet of cats compared with estimated encounter frequencies, whereas fast-running dragons, knob-tailed geckoes (Nephrurus) and echidnas (Tachyglossus aculeatus) were not recorded from cat stomachs despite being relatively abundant. Rabbits (Oryctolagus cuniculus), rodents and fruits were the most frequently recorded items in fox stomachs. This study reinforces that targeted management of feral cat populations should be considered in concert with control of canids in sustainable recovery programs for warru and other cat-vulnerable species.

Population monitoring of an urban gliding mammal in eastern Australia

Long-term monitoring is an important element of species conservation. This study describes changes in the size of a squirrel glider (Petaurus norfolcensis) population over a 10-year period. The population occupied a 45-ha forest remnant within the urban area of Brisbane. Gliders were tagged from 25 nights of trapping during 2006–08 and from 16 nights of trapping in 2015. Population modelling was used to estimate adult population size. This suggested the adult population comprised 30–40 individuals at the beginning and end of the 10-year period. It reached a peak of 70 individuals in mid-2007. These data suggest that the study area contains a small population that is prone to interannual variation but there was no evidence of it being in decline. Survival estimates during 2006–08 were equivalent to those estimated for a larger population in Victoria. Population monitoring should be continued to determine how resilient this population is to population decline and to investigate factors that may cause decline. This study provides an example of an approach that could be used to monitor threatened populations of the squirrel glider.

Mammal conservation and invasive species control in Australia: harnessing a potential extinction machine

The catastrophic declines and extinctions of a unique Gondwana-derived Australian mammalian fauna is a wildlife tragedy of epic proportions that remains to be played out. Four alien species in particular, rabbits (Oryctolagus cuniculus), foxes (Vulpes vulpes), feral cats (Felis catus) and cane toads (Rhinella marina) are recognised as ongoing threats, but protective control protocols consist of holding actions that currently require never-ending ecosystem subsidies (typically, culling and fencing). Recent revolutionary developments in cell biology and gene engineering – the CRISPR invention – has enabled the construction of gene drives that offer the prospect of controlling these species more efficiently indeed, even the possibility of extirpating these species from Australia. The conservation potential of these new technologies is described and recommendations are made.

Reduced efficacy of baiting programs for invasive species: some mechanisms and management implications

‘Bait-resistance’ is defined as progressive decreases in bait efficacy in controlled pest species populations. Understanding the mechanisms by which bait-resistance can develop is important for the sustainable control of pests worldwide, for both wildlife conservation programs and agricultural production. Bait-resistance is influenced by both behavioural (innate and learned bait-avoidance behaviour) and physiological aspects of the target pest species (its natural diet, its body mass, the mode of action of the toxin, and the animal’s ability to biochemically break down the toxin). In this review, we summarise the scientific literature, discuss factors that can lead to innate and learned aversion to baits, as well as physiological tolerance. We address the question of whether bait avoidance or tolerance to 1080 could develop in the red fox (Vulpes vulpes), an introduced predator of significant economic and environmental importance in Australia. Sublethal poisoning has been identified as the primary cause of both bait avoidance and increased toxin-tolerance, and so, finally, we provide examples of how management actions can minimise the risk of sublethal baits in pest species populations.