Habitat selection by vulnerable golden bandicoots in the arid zone

In 2010, vulnerable golden bandicoots (Isoodon auratus) were translocated from Barrow Island, Western Australia, to a mainland predator-free enclosure on the Matuwa Indigenous Protected Area. Golden bandicoots were once widespread throughout a variety of arid and semiarid habitats of central and northern Australia. Like many small-to-medium-sized marsupials, the species has severely declined since colonization and has been reduced to only four remnant natural populations. Between 2010 and 2020, the reintroduced population of golden bandicoots on Matuwa was monitored via capture-mark-recapture data collection, which was used in spatially explicit capture-recapture analysis to monitor their abundance over time. In 2014, we used VHF transmitters to examine the home range and habitat selection of 20 golden bandicoots in the enclosure over a six-week period. We used compositional analysis to compare the use of four habitat types. Golden bandicoot abundance in the enclosure slowly increased between 2010 and 2014 and has since plateaued at approximately one quarter of the density observed in the founding population on Barrow Island. The population may have plateaued because some bandicoots escape through the fence. Golden bandicoots used habitats dominated by scattered shrubland with spinifex grass more than expected given the habitat's availability. Nocturnal foraging range was influenced by sex and trapping location, whereas diurnal refuge habitat, which was typically under a spinifex hummock with minimal overstory vegetation, was consistent across sex and trapping location. Our work suggests that diurnal refuge habitat may be an important factor for the success of proposed translocations of golden bandicoots.

ANIMAL PHYSIOLOGY. Exceptionally low daily energy expenditure in the bamboo-eating giant panda

The carnivoran giant panda has a specialized bamboo diet, to which its alimentary tract is poorly adapted. Measurements of daily energy expenditure across five captive and three wild pandas averaged 5.2 megajoules (MJ)/day, only 37.7% of the predicted value (13.8 MJ/day). For the wild pandas, the mean was 6.2 MJ/day, or 45% of the mammalian expectation. Pandas achieve this exceptionally low expenditure in part by reduced sizes of several vital organs and low physical activity. In addition, circulating levels of thyroid hormones thyroxine (T4) and triiodothyronine (T3) averaged 46.9 and 64%, respectively, of the levels expected for a eutherian mammal of comparable size. A giant panda-unique mutation in the DUOX2 gene, critical for thyroid hormone synthesis, might explain these low thyroid hormone levels. A combination of morphological, behavioral, physiological, and genetic adaptations, leading to low energy expenditure, likely enables giant pandas to survive on a bamboo diet.

A review of the nutrition of Australian peramelid marsupials

European settlement has had a dramatic impact on the distribution and abundance of peramelid (bandicoot and bilby) marsupials. Predation and competition from introduced species and altered habitat have been implicated in their decline or extinction. Bandicoots and bilbies inhabit a broad range of habitats in Australia. Research on the distribution, morphology, gastrointestinal histology, lactation, metabolism and nutritional physiology of extant peramelid species has increased in the last few decades. This paper provides a review that encompasses recent nutritional-based research. Peramelid research is mostly limited to only three species – Isoodon macrourus, Perameles nasuta and Macrotis lagotis – which prevents effective comparisons between species. Peramelids are broadly classified as omnivores and possess relatively uncomplicated gastrointestinal tracts. The caecum is the region of greatest diversity among species. The relatively large caecum of Chaeropus ecaudatus supports the theory that this species may have been the only herbivorous peramelid. The caecum of M. lagotis is less pronounced than other species and is continuous with the proximal colon. M. lagotis also has a longer total colon length, which aids water conservation to ensure survival in an arid environment. Temperate-zone species such as I. macrourus, I. obesulus and P. nasuta are more similar to each other with respect to gastrointestinal morphology than either C. ecaudatus or M. lagotis. Additional research on the morphometrics of the gastrointestinal tracts of P. gunnii, P. bougainville, P. eremiana, M. leucura and I. auratus would enable further comparisons to determine whether differences are a result of geographic distribution, habitat preference or variation between genera and/or individual species. Currently, histological information of the gastrointestinal tract is limited to the small intestine of P. nasuta and I. macrourus. The histology of the small intestine of the weaned juvenile I. macrourus more closely resembles that of P. nasuta pouch young than P. nasuta adults. The younger bandicoots possessed villi whereas in the adult P. nasuta and I. macrourus villi were arranged in a zig-zag formation. The reason for the zig-zag formation of the villi and the function it may serve remains unclear. Detailed nutritional research on captive M. lagotis, I. macrourus and P. nasuta indicate that the two temperate-zone species – I. macrourus and P. nasuta – are more similar to each other than to the arid-dwelling M. lagotis. Detailed nutritional studies are required on all species, both free-living and captive. Experimental diets do not always accurately reflect a natural diet, which means that results from captive studies may not reflect the situation for free-living animals. The hindgut of peramelids is the main region for retention of digesta, and presumably where microbial digestion occurs. However, no studies have been undertaken to examine the microflora of the gastrointestinal tract of bandicoots or the bilby. As captive husbandry is an important tool in conservation management, it should also improve their successful maintenance in captivity by the provision of diets that better meet their nutritional requirements.

Diet of the bilby (Macrotis lagotis) in relation to substrate, fire and rainfall characteristics in the Tanami Desert

This study uses analysis of faecal pellets to assess the diet of the bilby (Macrotis lagotis) in an area spanning over 230 000 km2 in the Tanami Desert, Northern Territory. More specifically, we examine the link between diet composition, bilby prevalence and the landscape variables of fire, rainfall and substrate. Seed promoted by fire, particularly of Yakirra australiense, was found to be one of the most important components of the diet and constituted ~36% of the relative abundance of identifiable food particles. Bulb from Cyperus bulbosus was also an important component of the diet (18.5% relative abundance). Invertebrates accounted for 39% of the identifable food particles, and termites and beetles were the most common types. Bulb and seed formed a greater component of the diet in the central part of the study area where bilbies were more prevalent. Conversely, invertebrates were more dominant in the bilby diet on the northern and southern periphery of the Tanami Desert. Substrate type and antecedent rainfall associated significantly with the amount of seed from fire-promoted plants and total plant contained in the diet. Time since fire was an additional factor associated with the abundance of dietary fire-promoted seed. This suggests that the spatial and temporal variability of these landscape variables play an important role in controlling the availability of seed and bulb resources used by the bilby, and thus affect bilby prevalence. The results support the proposition that seed and bulb plant foods are exploited opportunistically and invertebrates, especially termites, are relied upon when plant food resources are scarce. Furthermore, the findings indicate that fire management could be used as a means to increase the favourability of habitat for the bilby in parts of its current range.

Ecophysiology and nutritional niche of the bilby (Macrotis lagotis), an omnivorous marsupial from inland Australia: a review

The bilby (Macrotis lagotis) is a small omnivorous marsupial that was once widespread but is now restricted to the most arid margins of its former range. It feeds on a mixture of invertebrates (mainly ants and termites) and plant material (mainly seeds and bulbs), most of which is below ground. Measurements of the energy and water requirements of free-living bilbies and of the maintenance nitrogen requirements of captive animals provided the basis for an explanation for its continued survival in the Australian arid zone. Measurements of the mean retention times of inert markers for the solute and particulate phases of digesta revealed no selective retention of solutes and small particles in the caecum. Lack of selective digesta retention in the bilby hindgut helps to explain why the plant component of their diet consists predominantly of seeds and bulbs of relatively low fibre content. This is in contrast to the stems and leaves eaten by other bandicoots, all of which appear to have a colonic separation mechanism that not only selectively retains small particles in the caecum but also facilitates the passage of large fibrous particles through the colon. The ability of the bilby to survive in the Australian arid zone is related to low water and nitrogen requirements and the abundance of ants, termites, bulbs and seeds. Foraging efficiency is maximised by exploiting the underground nests of seed-harvesting ants.

Energetics of free-ranging mammals, reptiles, and birds

We summarize the recent information on field metabolic rates (FMR) of wild terrestrial vertebrates as determined by the doubly labeled water technique. Allometric (scaling) relationships are calculated for mammals (79 species), reptiles (55 species), and birds (95 species) and for various taxonomic, dietary, and habitat groups within these categories. Exponential equations based on body mass are offered for predicting rates of daily energy expenditure and daily food requirements of free-ranging mammals, reptiles, and birds. Significant scaling differences between various taxa, dietary, and habitat groups (detected by analysis of covariance with P < or = 0.05) include the following: (a) The allometric slope for reptiles (0.889) is greater than that for mammals (0.734), which is greater than that for birds (0.681); (b) the slope for eutherian mammals (0.772) is greater than that for marsupial mammals (0.590); (c) among families of birds, slopes do not differ but elevations (intercepts) do, with passerine and procellariid birds having relatively high FMRs and gallinaceous birds having low FMRs; (d) Scleroglossan lizards have a higher slope (0.949) than do Iguanian lizards (0.793); (e) desert mammals have a higher slope (0.785) than do nondesert mammals; (f) marine birds have relatively high FMRs and desert birds have low FMRs; and (g) carnivorous mammals have a relatively high slope and carnivorous, insectivorous, and nectarivorous birds have relatively higher FMRs than do omnivores and granivores. The difference detected between passerine and nonpasserine birds reported in earlier reviews is not evident in the larger data set analyzed here. When the results are adjusted for phylogenetic effects using independent contrasts analysis, the difference between allometric slopes for marsupials and eutherians is no longer significant and the slope difference between Scleroglossan and Iguanian lizards disappears as well, but other taxonomic differences remain significant. Possible causes of the unexplained variations in FMR that could improve our currently inaccurate FMR prediction capabilities should be evaluated, including many important groups of terrestrial vertebrates that remain under- or unstudied and such factors as reproductive, thermoregulatory, social, and predator-avoidance behavior.