756 H. Bannister et al.


months after release, the diet of captive-bred houbara bus- tards Chlamydotis undulatawas the same as their wild-born counterparts (Bourass & Hingrat, 2015), but the time taken for the birds to adjust their diets was unknown. Many prac- titioners provide supplementary food or water during the acclimatization period in an attempt to ease the transition, but the usefulness of this has been debated (Rickett et al., 2013;Moseby et al., 2014). Understanding the diet of a rein- troduced species and how it changes over time is useful in assessing whether dietary components are available in sufficient quantities for long-term population persistence. Dietary studies can contribute to both understanding the ecology of a species and improving reintroduction success of future projects. We investigated the diet of a reintroduced population of


brushtail possums Trichosurus vulpecula in semi-arid South Australia over a 12 month period following reintroduction. The brushtail possum is a widely distributed Australian marsupial, but has disappeared from.50% of its historical range since European settlement, with declines most pro- nounced in the arid zone (Kerle, 1984; Kerle et al., 1992). Predominantly arboreal, brushtail possums usually forage in the canopy, consuming plants such as Eucalyptus, Acacia, Agonis and Santalum, but sometimes forage on the ground, consuming grasses, herbs and fungi (Fitzgerald, 1984;Kerle, 1984; Evans, 1992; How & Hillcox, 2000). Dominant plant species in their diet vary with location and environment. brushtail possums occasionally consume invertebrates and birds’ eggs (Foulkes, 2001; Cruz et al., 2012). In the arid zone, these possums prefer plants that are high in moisture, nutrients and dry matter digestibility, with low levels of toxins (Foulkes, 2001). The species was introduced to New Zealand, where its diet has since been well studied (e.g. Brown et al., 1993; Owen & Norton, 1995), but because of differences in habitat as well as a differing niche we only discuss our findings in the context of the species’ native distribution. Using DNA sequencing to identify dietary components,


we investigated whether brushtail possum diet changed with time since release, taking into account variation in food availability assessed using monthly vegetation surveys. We hypothesized that after accounting for availability, the diet would initially contain a high diversity and richness of food items as possums explored their new environment, but that this would decrease over time as preferred foods were located, thus increasing selectivity. The diet should stabilize, relative to availability, once possums have acclima- tized to the release site. We investigated whether possums favoured certain plant height classes, which can relate to predation risk, and evaluated sex differences in the diet. We also investigated any effect of rainfall, given the influence it can haveonaridzonesystems.


Study area


Brushtail possumswere reintroduced to c. 20%ofthe 93,400 ha Ikara-Flinders Ranges National Park (Fig. 1) in semi-arid South Australia in June 2015 (Bannister et al., 2020,Moseby et al., 2020). The species became regionally extinct in the 1940s (Kerle et al., 1992). Prior to being declared a Na- tional Park in 1970, significant land degradation occurred as a result of overgrazing by domestic stock (from the 1850s) and introduced herbivores (Mincham, 1996; Robinson, 2012). The Bounceback Project was initiated in 1992 and involved the removal of introduced foxes Vulpes vulpes, goats Capra hircus and rabbits Oryctolagus cuniculus (Alexander et al., 1997;Robinson, 2012), but goats and rabbits persist (Smith, 1996; Brandle et al., 2018) along with overabundant native macropods (Macropus rufus, Macropus robustus and Macro- pus fuliginosus), arresting the regeneration and recruitment of many plants. Vegetation types consist of open woodlands (Callitris glaucophylla interspersed with Eucalyptus inter- texta), or Eucalyptus camaldulensis floodouts (where flood- water infrequently overflows), E. camaldulensis creeklines, mallee (Eucalyptus spp.), shrubland and grassland.


Methods


We studied the brushtail possums’ diet over 12 months (August 2015–July 2016), commencing 1 month after ani- mals had been released, to avoid monitoring during a post- release period of containment and supplementary feeding for some animals. Scats were collected from trapped pos- sums (baited with peanut butter and rolled oats or apple and peanut butter), with an average of 44 ± SE 3 days be- tween collections from the same individual. We recorded the location of collected scats using a GPS (Fig. 1) and docu- mented the identity, sex, age, body mass, body condition and reproductive status of each possum. Because possums use shelter sites, we collected scats from some sites multiple times, from either the same or different individuals. Samples


were temporarily stored at −4 °C after collection and were then transferred to a−20 °C freezer where they were stored until being analysed. Unless specified otherwise, methods


and results refer to the consumption of plants only; the con- sumption of birds and invertebrates is discussed separately. To determine the environmental availability of plant


genera, we conducted monthly vegetation surveys. Sur- veys were conducted within the two habitat types used by possums for shelter: creekline and woodland (including floodouts). Each survey involved recording the presence and a visual estimate of per cent cover for each plant species within a 50 m radius of a shelter tree, usually also a trap site. When identification was not possible in the field a photo and sample were taken for subsequent identification.


Oryx, 2021, 55(5), 755–764 © The Author(s), 2020. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S0030605319000991


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