Ecology, energetics and thermal biology of sugar gliders

'Petaurus breviceps' inhabit tropical to cool-temperate regions within Australia and New Guinea. Despite their small body size (115-160 g) populations persist even in areas such as the New England region, where ambient temperature (Ta) frequently falls below 0°C over winter. Small mammals encounter a variety of energetic stresses at low Ta as a result or high thermal conductance requiring high metabolic rates (MR) for normothermic thermoregulation. Additionally insectivorous and nectarivorous species, such as sugar gliders, are confronted with seasonal reductions to food resources over winter. In order to survive and reproduce under these conditions, sugar gliders must employ a variety of behavioural and physiological strategies that include huddling and daily torpor. Although these strategies appear pivotal to their survival,almost all available information on this species is derived from captive animals and little is known on the seasonal adjustments of wild sugar gliders in terms of their thermal biology and behaviour. Moreover, little is known about the extent to which these adjustments are governed by reduced food availability and/or detrimental environmental conditions

Rabies disease dynamics in naȉve dog populations in Australia

Currently, Australia is free from terrestrial rabies but an incursion from nearby Indonesia, where the virus is endemic, is a feasible threat. Here, we aimed to determine whether the response to a simulated rabies incursion would vary between three extant Australian dog populations; free-roaming domestic dogs from a remote indigenous community in northern Australia, and free-roaming domestic and wild dogs in peri-urban areas of north-east New South Wales. We further sought to predict how different management strategies impacted disease dynamics in these populations. We used simple stochastic state-transition models and dog demographic and contact rate data from the three dog populations to simulate rabies spread, and used global and local sensitivity analyses to determine effects of model parameters. To identify the most effective control options, dog removal andvaccination strategies were also simulated. Responses to simulated rabies incursions varied between the dog populations. Free-roaming domestic dogs from north-east New South Wales exhibited the lowest risk for rabies maintenance and spread. Due to low containment and high contact rates, rabies progressed rapidly through free-roaming dogs from the remote indigenous community in northern Australia. In contrast, rabies remained at relatively low levels within the north-east New South Wales wild dog population for over a year prior to an epidemic. Across all scenarios, sensitivity analyses revealed that contact rates and the probability of transmission were the most important drivers of the number of infectious individuals within a population. The number of infectious individuals was less sensitive to birth and death rates. Removal of dogs as a control strategy was not effective for any population modelled, while vaccination rates in excess of 70% of the population resulted in significant reductions in disease progression. The variability in response between these distinct dog groups to a rabies incursion, suggests that a blanket approach to management would not be effective or feasible to control rabies in Australia. Control strategies that take into account the different population and behavioural characteristics of these doggroups will maximise the likelihood of effective and efficient rabies control in Australia

Quantifying effects of wild dogs, domestic dogs and humans on the spread of rabies in Australia

Rabies is a preventable viral zoonosis that causes inflammation of the brain, and eventually death, in infected mammals. With few exceptions, including Australia, terrestrial rabies can be found worldwide. More than 55,000 deaths from rabies infection are reported annually; these are mainly in Asia and Africa where the primary reservoir is the domestic dog. Despite ongoing control efforts in Indonesia, canine rabies remains a disease of critical concern there. Although rabies is not endemic in Australia, at less than 300km away in Indonesia, a rabies incursion is a likely and imminent threat. To improve preparedness for a canine rabies outbreak in Australia, I collected data on a number of extant dog populations in northern and eastern Australia. I used a range of methods including self-administered questionnaires, GPS telemetry collars, camera trapping and mark-recapture studies. Using my own data and parameters collected from the wider literature, I developed state-transition models to determine how rabies could spread through these dog populations. Finally, I used these same models to evaluate a range of control strategies, including dog removal and vaccination, to identify the most effective options for reducing impacts in Australian communities following a rabies incursion. Model outputs suggested that rabies will progress differently within functionally different dog populations present within Australia. Restrained domestic dogs posed limited risk for rabies transmission, because interactions with other dogs were limited and generally supervised by owners. Free-roaming domestic and hunting dogs will likely play an important role in rabies transmission in some situations only, primarily based on their ability to roam, access to other free-roaming dogs and their interactions within and between dog groups. Wild dogs (including dingoes) proved the most critical type of dog for rabies spread and maintenance in Australia, because they are widely distributed, often in high abundance, roam over large distances and frequently interact. I found that time to detection for rabies in wild dogs will likely be lengthy, probably due to low infection rates prior to an epidemic and limited contact with humans, relative to the other categories of dog that I studied. Further, the capacity of authorities to implement effective control strategies for wild dogs will likely be restricted because of limited access to individual animals. The economic costs of controlling a rabies outbreak involving wild dogs will be substantial and likely equivalent to the costs for extensive aerially-based wild dog control that are currently used in some areas of Australia (~Aus$34 km-2). Australia’s current plans to address rabies incursions, which were developed in the 1990s are clearly outdated. My findings reveal that revision of these plans, taking specific account of relevant differences between restrained domestic dogs, free-roaming domestic dogs and extensive wild dog populations is necessary to ensure that Australia is adequately prepared for the arrival of canine rabies

Post-fire recovery of torpor and activity patterns of a small mammal

To cope with the post-fire challenges of decreased availability of food and shelter, brown antechinus (Antechinus stuartii), a small marsupial mammal, increase the use of energy conserving torpor and reduce activity. However, it is not known how long it takes for animals to resume pre-fire torpor and activity patterns during the recovery of burnt habitat. Therefore, we tested the hypothesis that antechinus will adjust torpor use and activity after a fire depending on vegetation recovery. We simultaneously quantified torpor and activity patterns for female antechinus from three adjacent areas: (i) the area of a management burn one year post-fire, (ii) an area that was burned two years prior and (iii) a control area. In comparison to shortly after the management burn, antechinus in all three groups displayed less frequent and less pronounced torpor while being more active. We provide the first evidence that only one year post-fire antechinus resume pre-fire torpor and activity patterns, likely in response to the return of herbaceous ground cover and foraging opportunities

Evidence For An Extended Reproductive Season In The Spotted-Tailed Quoll 'Dasyurus Maculatus'

Spotted-Tailed quolls ('Dasyurus maculatus') raise only one litter with a maximum of six young per year. For quolls the breeding season starts in winter with mating usually occurring in June / July. Young are born about three weeks later (Jones et al. 2001) and available records indicate that generally young are born not later than August. Pouch young remain permanently attached to the teats for about seven weeks (Fleay 1940; Troughton 1954; Settle 1978) and have been observed between July and mid October (Jones et al. 2001; Belcher 2003; Körtner et al. 2004). In captivity, young are weaned between 120-150 days after birth and in the wild lactating females have not been observed after December (Fleay 1940; Settle 1978; Jones et al. 2001). At weaning young have reached a body mass between 300-600 g, about one third of their mother’s size (Fleay 1940; Settle 1978; Belcher 2003)

The key to winter survival: daily torpor in a small arid-zone marsupial

Mammalian hibernation, which lasts on average for about 6 months, can reduce energy expenditure by >90% in comparison to active individuals. In contrast, the widely held view is that daily torpor reduces energy expenditure usually by about 30%, is employed for a few hours every few days, and often occurs only under acute energetic stress. This interpretation is largely based on laboratory studies, whereas knowledge on daily torpor in the field is scant. We used temperature telemetry to quantify thermal biology and activity patterns of a small arid-zone marsupial, the stripe-faced dunnart 'Sminthopsis macroura' (16.9g), in the wild and to test the hypothesis that daily torpor is a crucial survival strategy of this species in winter. All individuals entered torpor daily with the exception of a single male that remained normothermic for a single day (torpor on 212 of 213 observation days, 99.5%). Torpor was employed at air temperatures (Ta) ranging from approximately −1°C to 36°C. Dunnarts usually entered torpor during the night and aroused at midday with the daily increase of Ta. Torpor was on average about twice as long (mean 11.0±4.7h, n=8) than in captivity. Animals employed sun basking during rewarming, reduced foraging time significantly, and occasionally omitted activity for several days in sequence. Consequently, we estimate that daily torpor in this species can reduce daily energy expenditure by up to 90%. Our study shows that for wild stripe-faced dunnarts daily torpor is an essential mechanism for overcoming energetic challenges during winter and that torpor data obtained in the laboratory can substantially underestimate the ecological significance of daily torpor in the wild

Activity and torpor in two sympatric Australian desert marsupials

Many biological variables related to energy turnover including torpor, the most efficient energy-saving mechanism available to mammals, scale with body size, but the implications for animals living in their natural environment remain largely unknown. We used radio-telemetry to obtain the first data on the activity patterns and torpor use of two sympatric, free-ranging dasyurid marsupials, the stripe-faced dunnart 'Sminthopsis macroura' (16.6±1.5 g) and the more than six-times larger kowari 'Dasyuroides byrnei' (109.4±16.4 g), during winter in arid Queensland, Australia. Eight dunnarts and six kowaries were surgically implanted with temperature-sensitive radio-transmitters and monitored for 14-59 days. Both species commenced activity shortly after sunset, but while kowaries remained active through most of the night, dunnarts usually returned to their burrows before midnight. In dunnarts, short activity was associated with the frequent use of daily torpor (99.1% of observation days). Torpor often commenced at night, with body temperature (Tb) decreasing to a minimum of 11.3 °C, and torpor lasted up to 26 h. In contrast, only 50% of the kowaries entered torpor and torpor was brief (maximum 4 h), shallow (minimum Tb 25.3 °C) and restricted to the daytime rest-phase. Our study suggests that in winter, the smaller dunnarts can remain active only during the warmer first half of the night and energy-saving torpor becomes part of their daily routine. In contrast, it appears that the larger kowaries are less affected by cold winter nights and can maintain high night-time activity levels and commence reproduction already in winter. Hence, they enter torpor only occasionally and only during the rest phase

The immediate impact of 1080 aerial baiting to control wild dogs on a spotted-tailed quoll population

In eastern Australia, the spotted-tailed quoll (Dasyurus maculatus) is the species thought to be most likely at risk from aerial baiting with compound 1080 to control wild dogs (Canis lupus familiaris and C. l. dingo). Although it is known that quolls occasionally die of 1080 poisoning, the broader impact on populations remains unresolved. We therefore assessed the impact of a regular aerial baiting campaign on a population of spotted-tailed quolls. Baiting with 1080 meat baits was conducted by the local Wild Dog Control Association and followed the same procedure as in previous years with the exception that the biomarker, rhodamine B, was added to the baits. Prior to the baiting, 36 quolls were trapped and fitted with mortality radio-collars; 31 of these collars were still functional at the time of baiting. Quolls were monitored from a helicopter and on the ground until retrapped 5–9 weeks after baiting. Transmitters were then removed and a sample of vibrissae was taken for rhodamine B analysis. Carcasses found were analysed for 1080. Predator numbers were assessed before and after baiting using track pads across trails. Among the initial 36 radio-collared quolls, nine mortalities were recorded during the course of the study (seven after baiting). Only one of the nine deaths could be directly attributed to 1080 poisoning. In addition, vibrissae from five of the 35 individuals sampled after baiting were marked with rhodamine B, indicating that these individuals had consumed bait, and survived. Consequently, mortality attributable to this particular aerial baiting campaign was low, apparently because few quolls ate bait and most of those that did survived. Track counts for predators indicated a significant decrease in dog and fox numbers after baiting. Cat activity remained unchanged and the number of quoll tracks increased

Hibernation and daily torpor in Australian mammals

Torpor is the most effective means for energy conservation available to mammals and is characterized by substantial reductions in body temperature (Tb) and metabolic rate (MR). Most Australian terrestrial mammals are small with high mass-specific energy requirements and, although it is widely believed that torpor is not needed in a 'warm' country like Australia, a large number of species are heterothermic (i.e. capable of changing Tb, in contrast to homeothermic mammals with a constant high Tb). These heterothermic species (estimated >43% of terrestrial Australian native mammals) employ periods of daily torpor or prolonged multi-day torpor (hibernation) to conserve energy. Daily torpor is used by dasyurids (e.g. dunnarts, antechinus, quolls), myrmecobiids (numbat), tarsipedids (honey-possum), petaurid possums (e.g. sugar glider), rodents (but only known in the introduced house mouse), and small megabats (blossom-bats). During daily torpor, Tb is reduced from ~35°C during the active or normothermic phase to ~10-25°C during torpor, and the torpor MR (TMR) is ~30% of the basal metabolic rate (BMR). Daily torpor is often, but not exclusively, used during the rest phase and, between bouts of torpor, animals usually forage and feed. Recent evidence shows that free-ranging arid zone dasyurids may employ daily torpor on every day in winter and that torpor may last twice as long as in captivity (often up to around 20 hours), which will reduce energy expenditure and thereby food requirements by up to 80%. Hibernation or prolonged torpor has been observed in the Monotremes (echidna), marsupials (pygmy-possums and feathertail glider) and insectivorous bats (e.g. long-eared bats). During prolonged torpor, which often, but not exclusively, is expressed in winter, Tb is usually reduced to a minimum of ~0-10°C, and torpor bouts may last for several days or weeks, but in all species periodic arousals with brief normothermic periods (hours) between bouts of torpor have been observed. The TMR during hibernation is extremely low and can be as little as 1-5% of the BMR; daily energy expenditure can be reduced to only 3% of that in active individuals permitting survival on stored body fat for months without the need to feed. Daily and prolonged torpor in many Australian mammals appear to be opportunistic and not only important for survival of adverse seasonal conditions, but apparently also for dealing with unpredictable events such as droughts and perhaps fires and floods. As torpor substantially reduces energy requirements its use will in turn reduce the need for foraging and consequently exposure to predators. Predator avoidance by employing torpor and minimising foraging may be one of the reasons why none of the known heterothermic Australian species has gone extinct. In contrast many of the similar-sized perceived homeothermic species, such as rodents and bandicoots, have suffered high rates of extinction possibly because they must forage long and frequently to meet large energetic demands and thus are more vulnerable to predation by introduced foxes and cats

Natural Use of Heterothermy by a Small, Tree-Roosting Bat during Summer

Little is known about the use of heterothermy by wild bats during summer, especially for tree-roosting species. Because thermal conditions within tree roosts can fluctuate widely with ambient temperature, which affects thermoregulatory energy expenditure during diurnal roosting, we measured skin temperatures of free-ranging male 'Nyctophilus geoffroyi' (8 g) to quantify the relation between summer torpor use and roost thermal conditions. Bats roosted under bark on the northern (sunny) side of trees and entered torpor every day, usually near sunrise. Bats exhibited two bouts of torpor on most days: the first occurred in the morning, was terminated by partially passive rewarming, and was followed by a period of normothermy during the warmest part of the day; a second torpor bout occurred in the late afternoon, with arousal near sunset. On the warmest days, bats had only a single, short morning bout. On the coolest days, bats remained torpid throughout the day, and one 2-d bout was observed. Thus, presumably owing to their poorly insulated roosts and the high energetic cost of normothermy at temperatures below 300C, the extent and timing of heterothermy was closely related to the cycle of diurnal temperatures. Our study indicates that torpor use is important for energy maintenance during summer diurnal roosting of 'N. geoffroyi' and likely of other small, tree-roosting bats