Tailoring release protocols to individual species and sites: one size does not fit all

Reintroduction programs for threatened species often include elaborate release strategies designed to improve success, but their advantages are rarely tested scientifically. We used a set of four experiments to demonstrate that the influence of release strategies on short-term reintroduction outcomes is related to both intrinsic and extrinsic factors. We compared different reintroduction strategies for three mammal species in an arid environment where exotic mammalian predators were removed. Wild greater stick-nest rats selected vegetation shelter sites with greater structural density than captive-bred rats, travelled further from the release site and experienced lower rates of mortality. In comparison, there was no difference in mortality or movement between wild and captive-bred greater bilbies. Burrowing bettongs and greater bilbies were also subjected to immediate and delayed release strategies and whilst no difference was detected in bilbies, bettongs that were subjected to delayed releases lost less weight and took less time to establish burrows than those that were immediately released. Interspecific differences in treatment response were attributed to predation risk, the nature of the release site, and behavioural traits such as shelter investment and sociality. Our varied results highlight the inadequacies of review articles focusing on optimum release protocols due to their attempt to generalise across species and release sites. We provide an example of a predictive model to guide future release strategy experimentation that recognises the range of intrinsic and extrinsic factors influencing reintroduction outcomes. We encourage researchers to treat programs experimentally, identify individual site and species characters that may influence release strategies and record data on movements, mortality, weight dynamics, and settling times and distances. The inherent issues of small sample size and low statistical power that plague most reintroduction experiments suggests there is also a need for increased standardisation and publication of data sets to enable appropriate meta-analyses to occur

Reintroduction strategies and life history traits for three species reintroduced during the study at the Arid Recovery Reserve.

<p>* = two separate releases.</p

The distance between successive daily fixes for delayed and immediate release burrowing bettongs after access to the Northern Paddock.

<p>Delayed release bettongs were kept in a release pen for three weeks prior to release. Bars denote 1 standard error.</p

Radiocollared animals released into the Northern Paddock, their initial characteristics, date of access to Northern Paddock and release treatment.

<p>For individuals that were opportunistically recaptured after completion of the study, the maximum time Known to Be Alive (KTBA) is included.</p><p>* = Date of translocation to the on-site containment pen, access to the rest of Northern Paddock occurred three weeks later.</p><p>+ = All females had pouch young when checked 7–9 weeks after release.</p

Weights of immediate (n = 8) and delayed (n = 6) release burrowing bettongs.

<p>The arrow indicates when release pen was first opened and delayed release animals allowed access to the Northern Paddock. Bars denote 1 standard error.</p

Average weights of delayed, immediate wild and immediate captive greater bilbies released into the Northern Paddock in 2003.

<p>Only three delayed and three immediate captive bilbies could be recaptured at seven to nine weeks for reweighing. Bars denote 1 standard error. Arrow indicates when release pen was opened.</p

Population genomics of a predatory mammal reveals patterns of decline and impacts of exposure to toxic toads

Mammal declines across northern Australia are one of the major biodiversity loss events occurring globally. There has been no regional assessment of the implications of these species declines for genomic diversity. To address this, we conducted a species-wide assessment of genomic diversity in the northern quoll (Dasyurus hallucatus), an Endangered marsupial carnivore. We used next generation sequencing methods to genotype 10,191 single nucleotide polymorphisms (SNPs) in 352 individuals from across a 3220-km length of the continent, investigating patterns of population genomic structure and diversity, and identifying loci showing signals of putative selection. We found strong heterogeneity in the distribution of genomic diversity across the continent, characterized by (i) biogeographical barriers driving hierarchical population structure through long-term isolation, and (ii) severe reductions in diversity resulting from population declines, exacerbated by the spread of introduced toxic cane toads (Rhinella marina). These results warn of a large ongoing loss of genomic diversity and associated adaptive capacity as mammals decline across northern Australia. Encouragingly, populations of the northern quoll established on toad-free islands by translocations appear to have maintained most of the initial genomic diversity after 16 years. By mapping patterns of genomic diversity within and among populations, and investigating these patterns in the context of population declines, we can provide conservation managers with data critical to informed decision-making. This includes the identification of populations that are candidates for genetic management, the importance of remnant island and insurance/translocated populations for the conservation of genetic diversity, and the characterization of putative evolutionarily significant units.</p