Cercartetus Nanus Research Articles

Eastern pygmy possum (Cercartetus nanus) populations persist in Central Coast forests after the Black Summer bushfires

The 2019–2020 Black Summer bushfires are an example of Australia’s climate-induced, changing fire regimes, where flora and fauna suffer both direct and indirect impacts as the result of large fires. The eastern pygmy possum (Cercartetus nanus) is a species that may be affected and, although its general ecology is well understood, there is limited knowledge of its response to wildfire. Using clusters of nest boxes across two state forests on the New South Wales Central Coast, detection histories were created from 2017 to 2023. Estimates of occupancy, detection and extinction were produced, where the top ranked model included Fire severity as a covariate of extinction. Extinction probability was highest in unburnt areas, 0.55 (95% CI = 0.13–0.82) and lowest in moderate fire severity areas, 0.15 (95% CI = 0.003–0.52), although all estimates were highly uncertain. Detection probability was 0.35 per cluster visit (95% CI = 0.26–0.45) and occupancy probability was 0.77 (95% CI = 0.39–0.98), indicating a high probability of occupancy at sites affected by fire. This suggests that eastern pygmy possums may benefit from post-fire resources, such as flowering shrubs, as well as their flexible den selection, providing a niche that other arboreal animals may be unable to exploit so soon post fire.

Regional Intraspecific Differences of Thermal Biology in a Marsupial Hibernator.

AbstractDuring periods of torpor, hibernators can reduce metabolic rate (MR) and body temperature (Tb) substantially. However, to avoid physiological dysfunction at low temperatures, they defend Tb at a critical minimum, often between ~0°C and 10°C via an increase in MR. Because thermoregulation during torpor requires extra energy, individuals with lower Tb's and thus minimal MR during torpor should be selected in colder climates. Such inter- and intraspecific variations occur in some placental mammals, but for the evolutionary separate marsupials, available information is scarce. Marsupial eastern pygmy possums (Cercartetus nanus; ~22 g body mass), widely distributed along the Australian southeastern coast including subtropical to alpine areas, were used to test the hypothesis that the defended Tb of torpid individuals is related to the climate of their habitat. Possums were captured from five regions, 1,515 km apart, with midwinter (July) minimum environmental temperatures (min Tenv's) ranging from -3.9°C to 6.6°C. Captive possums in deep torpor were slowly cooled with ambient temperature (Ta), while their MR was measured to determine the minimum torpor metabolic rate (TMR), the Ta at which their MR increased for thermoregulation (min Ta), and the corresponding minimum Tb (min Tb). Partial least squares regression analysis revealed that Ta and Tenv were the strongest explanatory variables for the min Tb. The min Tb and Ta were also correlated with latitude but not elevation of the capture sites. However, the best correlations were observed between the min Tenv and the min Tb and Ta for individuals experiencing min ; these individuals thermoconformed to min Ta's between -0.8°C and 3.7°C, and their min Tb ranged from 0.5°C to 6.0°C and was 0.5°C-2.6°C below the min Tenv at the capture site. In contrast, individuals experiencing a min Tenv of -3.9°C regulated Tb at or 4.5°C above the Tenv. The minimum TMR of all possums did not differ with Ta and thus did not differ among populations and was 2.6% of the basal MR. These data provide new evidence that thermal variables of marsupials are subject to regional intraspecific variation. It suggests that min Tb is a function of the min Tenv but only above 0°C, perhaps because the differential for torpid possums in the wild, at a min Tenv of -3.9°C, remains small enough to be compensated by a small increase in MR and does not require the physiological capability for a reduction of Tb below 0°C.

Long-term survival, temperature, and torpor patterns

Mammalian and avian torpor is highly effective in reducing energy expenditure. However, the extent of energy savings achieved and thus long-term survival appear to differ between species capable of multiday hibernation and species restricted to daily heterothermy, which could, however, be due to thermal effects. We tested how long-term survival on stored body fat (i.e. time to lean body mass), crucial for overcoming adverse periods, is related to the pattern of torpor expressed under different ambient temperatures (Ta: 7 °C typical of hibernation, 15 and 22 °C typical of daily torpor) in the small marsupial hibernator the pygmy-possum (Cercartetus nanus). Possums expressed torpor at all Tas and survived without food for 310 days on average at Ta 7 °C, 195 days at Ta 15 °C, and 127 days at Ta 22 °C. At Ta 7 and 15 °C, torpor bout duration (TBD) increased from < 1–3 to ~ 5–16 days over 2 months, whereas at Ta 22 °C, TBD remained at < 1 to ~ 2 days. At all Tas daily energy use was substantially lower and TBD and survival times of possums much longer (3–12 months) than in daily heterotherms (~ 10 days). Such pronounced differences in torpor patterns and survival times even under similar thermal conditions provide strong support for the concept that torpor in hibernators and daily heterotherms are physiologically distinct and have evolved for different ecological purposes.

Habitat use by the eastern pygmy-possum in a coastal woodland–heathland mosaic

Understanding patterns of habitat use is required to conserve species and to manage their habitats. I used detections of 156 individual eastern pygmy-possums (Cercartetus nanus) within artificial cavities to investigate habitat use across 18 ha of a woodland–heathland mosaic. Detection of breeding females was highest in autumn (March to May) and winter, during the flowering period of Banksia ericifolia. Detection was over two times higher in woodland compared with heathland. This pattern was not influenced by variation in flowering or hollow abundance, which were equivalent across the two habitats. Protection from the weather may drive this pattern. Adult males were detected most frequently in autumn, coinciding with the beginning of female reproduction. They were detected equally in woodland and heathland. Why detection was lower in winter and spring is unclear but may arise from female aggression, forcing males to use natural shelters away from lactating females. Subadults were detected most frequently in spring and summer, coinciding with independence and dispersal. Subadults preferred woodland, reflecting where they were reared. This study has provided new insights into the behavioural ecology of this species, but further studies are needed to better understand how foraging and breeding influence shelter site use.

Contrasting physiological responses to habitat degradation in two arboreal mammals

SummaryTo cope with the challenges presented by habitat degradation and loss, animals must often respond by adjusting physiological and behavioral mechanisms. Here we quantified physiological and behavioral traits, including body temperature and food consumption, of two mammals with differing thermoregulatory strategies in response to changes in climate and habitat. We show that both species responded to challenging climatic conditions by increasing torpor use to save energy, yet their responses were impacted by varying vegetation levels. Sugar gliders decreased torpor use in a dense habitat likely due to a signal of greater food production and protection from predators. Conversely, eastern pygmy possums employed more torpor perhaps to build up fat reserves in anticipation of leaner times. Indeed, in dense habitat eastern pygmy possums did not alter food intake yet showed an increase in body mass, whereas sugar gliders consumed less food and lost body mass, revealing the large energetic savings provided by torpor.

The diet of a Sooty Owl from Yarrangobilly Caves, NSW

ABSTRACT A total of 783 dietary items from a Sooty Owl Tyto tenebricosa tenebricosa with suspected partial xanthochromism (yellow plumage colouration) was identified from Yarrangobilly Caves, NSW. Observations of the owl at the cave and collection of feathers suggest that prey items accumulated between 2011 and 2018. A total of 12 mammal species was detected in the diet, with the Bush Rat Rattus fuscipes, Agile Antechinus Antechinus agilis, Sugar Glider Petaurus breviceps and Rabbit Oryctolagus cuniculus dominating. The diet also included three threatened species, the Eastern Pygmy Possum Cercartetus nanus, Smoky Mouse Pseudomys fumeus and Broad-toothed Rat Mastacomys fuscus. The diversity of prey identified in the diet contrasts markedly with that found in studies of subfossil deposits from the area, supporting evidence of extensive mammal declines since European settlement.

Sex and age differences in tree cavity dependence in a small arboreal marsupial

AbstractMany mammal species depend on tree cavities for shelter and for breeding. Some species may use tree cavities as well as other varied shelters, but the extent of their dependence on tree cavities is unknown. One such species is the eastern pygmy‐possum (Cercartetus nanus) from eastern Australia which typically shelters alone. Four key questions were addressed: (1) do different age and sex classes differ in their preferences for small (4 cm diameter) and large (10 cm diameter) cavities, (2) does the availability of large cavities influence female breeding status, (3) does the availability of large cavities influence where adult females and males are detected, and (4) does the availability of large cavities influence survival and abundance? Two 9‐ha plots containing few (≤2 per ha) ‘large’ natural cavities were provisioned with artificial cavities in different years. When plots were provisioned with small and large cavities, breeding females (n = 46) showed a pronounced preference for sheltering in the large cavities while adult males (n = 67) and subadults (n = 40) preferred the small cavities. When one plot and not the other was provisioned with large cavities, adult females were significantly more likely to be reproductive and be detected on the plot with large cavities, but survival was not influenced. Detection of adult males did not vary with large cavity provisioning. The abundance of adult pygmy‐possums varied among years, being higher on the plot provisioned with large cavities when the other plot was not provisioned, but equivalent when both were provisioned. The findings of this study are consistent with the hypothesis that breeding females are dependent on a large cavity to raise a litter. Other mammal species around the world are likely to exhibit similar but currently unrecognized shelter site strategies which have implications for their management.

Novel field observations of eucalypt sap feeding behaviour in the Eastern Pygmy-possum Cercartetus nanus

The Eastern Pygmy-possum Cercartetus nanu s is a small arboreal marsupial in the family Burramyidae that is threatened in parts of its range. Considered a generalist omnivore, its diet is known to include invertebrates, seeds, nectar and pollen. Tree sap has never before been recorded as a part of the diet of C. nanus . Here, we report on two observations of C. nanus feeding on eucalypt sap in south-eastern New South Wales.

Limits to alien black rats (Rattus rattus) acting as equivalent pollinators to extinct native small mammals: the influence of stem width on mammal activity at native Banksia ericifolia inflorescences

Alien species are a major cause of species extinctions globally and the effects of introductions can become substantial, especially once aliens become entrenched and impossible to eradicate. Some entrenched aliens may assume niches of extinct native species that are functionally similar, but the capacity of an alien to perform specialised ecological processes is unknown. Here we examine the potential for the alien black rat (Rattus rattus) to effectively pollinate native Banksia ericifolia in heath at North Head, Sydney where endemic mammalian pollinators such as brown antechinus (Antechinus stuartii) and eastern pygmy-possums (Cercartetus nanus) had been locally extinct prior to recent reintroductions. Using artificial inflorescences, we compared the use of inflorescences, visit frequency and duration of alien black rats to reintroduced natives according to the stem diameter of the inflorescence. Black rats were the most frequent visitor and they spent similar or more time at artificial inflorescences as natives, but they also spent more time visiting inflorescences with thicker stem diameters. In contrast, the native mammals visited artificial inflorescences regardless of the stem thickness. We suggest that, as black rats are heavier than the native mammals, this could limit their capacity as substitute pollinators of B. ericifolia. This finding shows the importance of understanding the extent of the benefits of aliens before relying on them as functional replacements for extinct natives.

Does temperature variation influence nest box use by the eastern pygmy-possum?

Cavity-using birds and mammals reliant on nest boxes may be negatively affected by the poor thermal buffering of nest boxes. I investigated whether nest box use by the eastern pygmy-possum (Cercartetus nanus) over a 4-year period was influenced by maximum ambient temperature, which ranged from 15.6 to 34.9°C during survey occasions. Occupancy modelling of 144 site detections over 30 survey occasions suggested that a model that included maximum temperature had little support whereas a model involving time-varying detection (i.e. detection differed across sample occasions) was the most plausible. I also investigated how temperatures in nest boxes and tree hollows varied over the four hottest days of summer, including one day when the temperature reached 40.6°C. Maximum temperatures were 3–4°C cooler in plywood nest boxes and 5–8°C cooler in tree hollows compared with ambient temperatures. Together, these results suggest that eastern pygmy-possums using nest boxes in coastal areas are unlikely to experience heat stress. Cavity-using species are a heterogeneous group such that empirical studies are required to identify those that may be vulnerable to heat stress if nest boxes are used to provide population support.

The interrelationship between torpor expression and nest site use of western and eastern pygmy-possums (Cercartetus spp.)

Physiology and behaviour are closely linked, making knowledge of the interaction between species’ energetics and activities important when attempting to understand how animals function in the wild. I examined torpor use by western pygmy-possums (Cercartetus concinnus) and eastern pygmy-possums (C. nanus) in relation to nest site characteristics and movement patterns. In coastal mallee heath in winter, C. concinnus nested beneath leaf litter at the base of dead Banksia ornata, where they employed torpor on 69% of observed days. In warm temperate sclerophyll forest, C. nanus nested in tree hollows of Eucalyptus spp. and used torpor on 64% of days in winter and 10% in summer. Torpor was used in nest sites that were buffered from outside temperature extremes. Both species frequently reused nest sites and while C. nanus was more likely to employ torpor in a previously used site, site familiarity did not influence torpor use for C. concinnus. Additionally, C. nanus was more likely to use torpor in hollows with a higher relative thickness in both seasons. No relationship was found between range size and the number of tracking days or capture body mass, though sample sizes were small. I suggest that the thermal attributes of nest sites influence torpor use for both species and this is likely vital for maintaining a positive energy balance, stressing the importance of preserving habitat with ample potential nest sites for conservation management.

Elevation induced variation in the breeding traits of a nectar‐feeding non‐flying mammal

AbstractFactors that influence reproduction in nectar‐feeding non‐flying mammals are poorly described. We investigated factors that may influence the breeding traits of the eastern pygmy‐possum (Cercartetus nanus), a small (25 g) nectar‐feeding marsupial from eastern Australia. Females at our coastal site produced 1–3 litters (frequently of 5–6 young) over an 8‐month period within the flowering period of the dominant food plant (Banksia ericifolia). The number of lactating females over time was highly correlated (R = 0.9) with the abundance of flowers on B. ericifolia, suggesting that flower availability has a substantial influence on breeding. To assess the generality of these findings and investigate whether elevation or latitude influence breeding in this species, we examined the breeding traits previously described at three other locations. Females on the tableland 70 km away produced one litter of 3–4 young over a 4‐month period within the flowering period of B. ericifolia, the dominant food plant. At other coastal and tableland locations 500 km away, coastal females produced larger numbered litters more often than tableland females. A hypothesis relating to minimum temperature appears the most plausible explanation for this pattern that reflects elevation but not latitude. The mean minimum temperature drops below 5 °C for 2–5 months each year at the tableland locations but not at all at the coastal locations. Low temperatures are known to reduce nectar secretion in the dominant food plants. Thus, although the breeding traits of the eastern pygmy‐possum are influenced by flowering in their dominant food plants, low temperature appears to impose a constraint on reproductive output.

Comparison of microhabitat use in young regrowth and unlogged forest by the eastern pygmy-possum (Cercartetus nanus)

We describe microhabitat use and response to disturbance by the eastern pygmy-possum (Cercartetus nanus) in heathy dry sclerophyll forest using spool-and-line-tracking. We compared unlogged forest with forest regenerating four years after selective logging. Structural and floristic attributes were scored along spool lines and compared with a random line for each possum. We found that possums (n = 23) selected areas based on both structural and floristic attributes. Possums selected dense understorey, especially that comprising flowering hairpin banksia (Banksia spinulosa) and Gymea lily (Doryanthes excelsa). Fallen logs were not selected by nocturnally active possums. Spool lines in regrowth forest had less eucalypt cover and more understorey cover (e.g. D. excelsa and B. spinulosa) than unlogged forest. Conversely, cover of Banksia serrata was less in regrowth than unlogged forest. Spool lines were commonly found both at ground level (mean = 52–57% of lengths) and above the ground (43–48% of lengths). There was no difference in the mean spool height between the logging treatments (regrowth: 0.47 ± 0.14 m; unlogged: 0.49 ± 0.10 m; ± s.e.). Overall, our results suggest that the dense, flowering understorey that regenerates after selective logging is suitable for use and is the primary attribute selected by active pygmy-possums.

Population density of the eastern pygmy-possum in a heath–woodland habitat

The eastern pygmy-possum (Cercartetus nanus) has posed a challenge in attempts to describe its population density due to low rates of capture, preference for patchy habitats and periodic influxes of subadult individuals. We conducted a mark–recapture study of this species using a grid of nest boxes in a 9-ha patch of banksia heath–woodland. We captured 54 adults across the two years of our study. We estimated the density of adult pygmy-possums to be 1.5–4.2 ha–1 from different population models. This is substantially lower than previous estimates in equivalent habitat because we focussed on adults and recognised that they were not confined to the area bounded by our grid. We captured 36 subadults over the two years but they could not be reliably modelled due to extremely low recapture rates, which reflect high rates of dispersal and also mortality. For this reason, only the number of adults should be used to characterise populations of this species. Further study is required to investigate population dynamics over time and to describe the density of eastern pygmy-possums in other habitats.

Heart rate dynamics in a marsupial hibernator.

The eastern pygmy possum (Cercartetus nanus) is a small marsupial that can express spontaneous short bouts of torpor, as well as multi-day bouts of deep hibernation. To examine heart rate (fH) control at various stages of torpor in a marsupial hibernator, and to see whether fH variability differs from that of deep placental hibernators, we used radiotelemetry to measure ECG and body temperature (Tb) while measuring the rate of O2 consumption and ventilation. fH and O2 consumption rate during euthermia were at a minimum (321±34 beats min-1, 0.705±0.048 ml O2 g-1 h-1) at an ambient temperature (Ta) of 31°C. fH had an inverse linear relationship with Ta to a maximum of 630±19 beats min-1 at a Ta of 20°C. During entry into torpor at a Ta of 20°C, fH slowed primarily as a result of episodic periods of cardiac activity where electrical activity of the heart occurred in groups of 3 or 4 heart beats. When Tb was stable at 24°C in these torpor bouts, the episodic nature of fH had disappeared (i.e. no asystoles) with a rate of 34±3 beats min-1 For multi-day bouts of deep torpor, Ta was lowered to 6.6±0.8°C. During these deep bouts of torpor, Tb reached a minimum of 8.0±1.0°C, with a minimum fH of 8 beats min-1 and a minimum O2 consumption rate of 0.029±0.07 ml O2g-1h-1 Shivering bouts occurred in deep torpor about every 8 min, during which ventilation occurred, and fH was elevated to 40 beats min-1 The duration of the QRS complex increased from 12 ms during euthermia to 69 ms at a Tb of 8°C. These findings demonstrate the dynamic functioning range of fH to be about 600 beats min-1 (∼80-fold), one of the largest known ranges in mammals. Our study shows that despite a separation of ∼160 million years, the control and function of the cardiac system seems indistinguishable in marsupial and placental hibernating mammals.

Monitoring ground-dwelling mammals, Eastern Bristlebird and Ground Parrot at Vincentia on the south coast of New South Wales

ABSTRACT Fauna surveys were conducted near the coastal village of Vincentia on the south coast of New South Wales from 2000 to 2014 in response to a proposal to extend a golf course. The surveys consisted of trapping ground-dwelling mammals along six, 200 m long transects and targeted surveys for the Eastern Bristlebird Dasyornis brachypterus and Ground Parrot Pezoporus wallicus. Eight native species of ground-dwelling mammal were trapped including the White-footed Dunnart Sminthopsis leucopus, Eastern Chestnut Mouse Pseudomys gracilicaudatus and Eastern Pygmy Possum Cercartetus nanus, species currently listed on the Threatened Species Conservation Act (1995) and the New Holland Mouse Pseudomys novaehollandiae listed as vulnerable under the Environment Protection and Biodiversity Conservation Act (1999). The most abundant mammals trapped were the Bush Rat Rattus fuscipes and the Brown Antechinus A. stuartii accounting for 67% and 14% of all Elliott trap captures, respectively. The survey provided the firs...

The influence of natural photoperiod on seasonal torpor expression of two opportunistic marsupial hibernators

Many mammals use torpor throughout the year but the individual contributions of environmental variables to seasonal changes in torpor expression are often difficult to tease apart. In many mammals, torpor is most often used opportunistically in response to decreased ambient temperature (T a ) and food availability, but information on how seasonally changing photoperiod per se influences torpor patterns is scant. Therefore, we quantified patterns of torpor use in response to natural photoperiod in captive marsupial pygmy-possums held at near-constant T a with a stable food supply over a period of 19months. Western pygmy-possums (Cercartetus concinnus) and eastern pygmy-possums (C. nanus) used spontaneous torpor in every month of the year; in total we measured >1100 individual torpor bouts. Torpor bout duration was >60% longer in winter than in summer and increased with decreasing day length for both species. Interestingly, the duration of torpor appeared to be adjusted at both the beginning and end of bouts because the time of entry into and rewarming from torpor relative to sunrise and sunset, respectively, changed with season. We propose that this reflects a synchronisation of torpor timing with foraging periods in the wild, which would enable animals to maintain a high body mass year-round by maximising both energy savings via torpor and energy input via food consumption. Our study suggests that photoperiod makes a significant contribution to the seasonal change in torpor bout duration of small hibernating mammals that use torpor throughout the year.

Can hibernators sense and evade fires? Olfactory acuity and locomotor performance during deep torpor.

Increased habitat fragmentation, global warming and other human activities have caused a rise in the frequency of wildfires worldwide. To reduce the risks of uncontrollable fires, prescribed burns are generally conducted during the colder months of the year, a time when in many mammals torpor is expressed regularly. Torpor is crucial for energy conservation, but the low body temperatures (T b) are associated with a decreased responsiveness and torpid animals might therefore face an increased mortality risk during fires. We tested whether hibernators in deep torpor (a) can respond to the smell of smoke and (b) can climb to avoid fires at T bs below normothermic levels. Our data show that torpid eastern pygmy-possums (Cercartetus nanus) are able to detect smoke and also can climb. All males aroused from torpor when the smoke stimulus was presented at an ambient temperature (T a) of 15°C (T b ∼18°C), whereas females only raised their heads. The responses were less pronounced at T a 10°C. The first coordinated movement of possums along a branch was observed at a mean T b of 15.6°C, and animals were even able to climb their prehensile tail when they reached a mean T b of 24.4°C. Our study shows that hibernators can sense smoke and move at low T b. However, our data also illustrate that at T b ≤13°C, C. nanus show decreased responsiveness and locomotor performance and highlight that prescribed burns during winter should be avoided on very cold days to allow torpid animals enough time to respond.

Population ecology of the eastern pygmy-possum (Cercartetus nanus) in a montane woodland in southern New South Wales

The population dynamics of nectar-feeding non-flying mammals are poorly documented. We investigated aspects of the population ecology of the eastern pygmy-possum (Cercartetus nanus) in southern New South Wales. We captured 65 individuals over a 4-year period during 5045 trap-nights and 1179 nest-box checks. The body mass of adult males (mean ± s.e. = 24.6 ± 1.0 g) was marginally not significantly different (P = 0.08) from that of non-parous adult females (28.2 ± 1.9 g). Females gave birth to a single litter each year of 3–4 young during February–May. No juveniles were detected in spring of any year. Mark–recapture modelling suggested that survival probability was constant over time (0.78) while recapture probability (0.04–0.81) varied with season and trap effort. The local population (estimated at ~20–25 individuals) underwent a regular seasonal variation in abundance, with a decline in spring coinciding with the cessation of flowering by Banksia. A population trough in spring has been observed elsewhere. This appears to represent some local migration from the study area, suggesting a strategy of high mobility to track floral resources. Conservation of this species will depend on a more detailed understanding of how flowering drives population dynamics.

High predation risk for a small mammal: the eastern pygmy-possum (Cercartetus nanus)

We report high rates of predation within a population of eastern pygmy-possum (Cercartetus nanus) near Sydney, observed during a study of the impacts of logging on the species. Predation by reptiles was observed on six of 61 radio-tracked pygmy-possums, while two were suspected of being taken by raptors. We further investigated predation by sooty owls (Tyto tenebricosa) by identifying remains in pellets. Pygmy-possums comprised 15% of the 126 dietary items identified. Predation occurred at both logged and unlogged sites in our study. We suggest that documented high rates of predation in our study could make the species vulnerable to altered predation regimes, such as influxes of feral predators, and highlight the need for a better understanding of any influence of logging on predator activity.