A comparative study of survival, recruitment and population growth in two translocated populations of the threatened greater bilby (Macrotis lagotis)

Abstract

Context Translocations have been widely used to re-establish populations of threatened Australian mammalian species. However, they are limited by the availability of sites where key threats can be effectively minimised or eliminated. Outside of ‘safe havens’, threats such as exotic predators, introduced herbivores and habitat degradation are often unable to be completely eliminated. Understanding how different threats affect Australian mammal populations can assist in prioritising threat-management actions outside of safe havens. AimsWe sought to determine whether translocations of the greater bilby to two sites in the temperate zone of South Australia could be successful when human-induced threats, such as prior habitat clearance, historic grazing, the presence of feral cats and European rabbits, could not be completely eliminated. Methods Greater bilbies were regularly cage trapped at two translocation sites and a capture–mark–recapture study was used to determine survival, recruitment and population growth at both sites. Key results Our study showed that bilbies were successfully translocated to an offshore island with a previous history of grazing and habitat clearance, but which was free of exotic predators. At a second site, a mainland exclosure with feral cats and European rabbits present, the bilby population declined over time. Adult bilbies had similar survival rates in both populations; however, the mainland bilby population had low recruitment rates and low numbers of subadults despite high adult female fecundity. ConclusionsThe results indicated that past grazing and habitat clearance did not prevent the bilby population on the offshore island establishing and reaching a high population density. In the mainland exclosure, the low recruitment is probably due to feral cats predating on subadult bilbies following pouch emergence. Implications The results demonstrated that the bilby, an ecologically flexible Australian marsupial, can be successfully translocated to sites with a history of habitat degradation if exotic predators are absent. At the mainland exclosure site, threat mitigation for bilbies should focus on control or eradication of the feral cats. The control of European rabbits without control of feral cats could lead to prey-switching by feral cats, further increasing predation pressure on the small bilby population.

The influence of drought, precipitation and fossorial mammal reintroduction on the density of fossorial arthropods and their burrows in arid Australia

“…Future studies may be able to detect trophic interactions between bilbies or other fossorial mammals and arthropods, which were largely undetectable in our study because of the short time frame and low population density. Fossorial mammals translocated to predator‐exclusion fences and island safe havens can reach remarkably high densities (Berris et al, 2020; Moseby et al, 2018; Smith et al, 2020). This may be a problem for the functional roles of the arthropods in providing food and refuges where the translocated species are arthropod predators.…”

“…While our bilby density was low, other wild bilby populations also have low densities (Augusteyn et al, 2020). Some translocated populations, however, can reach densities >100 bilbies/km 2 (Berris et al, 2020). Although we did not detect effects of bilbies in our study, we did find evidence for bilbies foraging harvester ant middens within our plots.…”

Feral Cats in the Subtropics of Australia—The Shamrock Station Irrigation Project

“…Experimental studies have shown that feral cats are a threat to bilbies unless they are present in very low densities [60]. These results are supported by reintroductions of bilbies to Venus Bay and Matuwa in Western Australia, and Thistle Island in South Australia, which found that it is possible to establish a viable population of bilbies where there has been historic grazing and habitat clearance, provided that no or very few exotic predators are present [33,60,61]. Given the high density of feral cats on Shamrock Station, initiating feral cat control is likely to benefit the bilby, enabling the survival of individuals that disperse out of the greater La Grange area [10].…”

High survivorship and rapid population growth of the greater bilby (Macrotis lagotis) reintroduced to a feral predator exclosure

“…Multiple interacting factors continue to threaten remaining wild bilby populations, with predation by feral cats and foxes recognised as key threats (Paltridge 2002;Moseby et al 2011;Burbidge et al 2014;Bradley et al 2015). To counteract these threats, bilbies have been successfully reintroduced to 10 fenced exclosures and one offshore island, where feral predators have been eradicated (Moseby and O'Donnell 2003;Berris et al 2020a;Palmer et al 2020;DCCEEW 2023).…”