Climate and behaviour influence thermal suitability of artificial hollows for a critically endangered mammal

Abstract

Artificial hollows are commonly used to mitigate the scarcity of den and nest sites that threatens fauna species globally, but there is a risk that these do not provide suitable microclimates for the populations they are intended to support. We monitored temperature, humidity and occupancy in artificial dens (nest boxes and chainsaw-carved cavities) provided for the critically endangered Leadbeater's possum (Gymnobelideus leadbeateri) in south-eastern Australian forests. Monitoring occurred over both winter and summer in five habitat types spanning a broad elevational gradient (110-1580 m asl). We then used a biophysical model to explore the physiological consequences of the den temperatures recorded, and the potential effectiveness of behavioural strategies in reducing thermoregulatory costs. Monitoring revealed that nest box temperatures tracked ambient over both seasons, ranging from À5.5°C to 48.5°C, while chainsaw hollows provided more stable internal conditions. However, we found that inferences regarding the thermal suitability of artificial dens were site-specific, and dependent upon habitat type, season and assumptions around behavioural strategies. During winter, behaviours such as the construction of large, insulative nests and huddling are likely critical in overcoming high energy costs associated with poorly insulated artificial dens. In contrast, during summer high thermoregulatory costs were predicted for the warmest (lowland) site and coincided with low nest box occupancy. Our study reinforces the importance of factoring in local climates, and behavioural and physiological strategies employed by target taxa, when implementing artificial den programs to support fauna populations.

Chainsaw hollows carved into live trees provide well insulated supplementary shelters for wildlife during extreme heat

“…Recent studies trialling the use of cavities carved directly into trees have reported promising results, with a range of native hollow-dependent birds and mammals visiting and using these novel supplementary shelters (Hurley and Harris 2014;Bengtsson and Wheater 2021;Terry et al 2021;Best et al 2022). However, little is known about microclimate conditions inside mechanically carved hollows (Griffiths et al 2018;McComb et al 2021), particularly during weather extremes. In this study, we used the opportunity presented by extremely hot weather that occurred during December 2019 (austral summer) in Melbourne, Australia, to compare microclimate conditions in plywood nest boxes, which are commonly used in habitat restoration and wildlife conservation programs (Macak 2020), with two relatively novel and untested types of artificial hollow that are increasingly being used across south-eastern Australia, namely (1) CHs (Griffiths et al 2020;McComb et al 2021;Terry et al 2021) and (2) LHs (Griffiths et al 2018).…”

Huddling nest use are the optimal strategies for heat conservation in a social marsupial: lessons from biophysical models

“…The use of biophysical models in physiological ecology dates back to Warren and Porter seminar paper (Porter and Gates, 1969; Tracy, 1972, see an update in Kearney and Porter, 2009), who defined the energy budget of animals as a balance equation of energy losses and gains in a variety of environments, type of organisms and thermal conditions. Later, a number of authors have applied them for predicting a variety of contexts (e.g., climatic impact on species range: Huey et al, 2012; Kearney et al, 2009; heat loss and behavioral thermoregulation in endotherms: Kenagy et al, 2002; McCafferty et al, 2011; reconstructing dinosaur physiology Seebacher, 2003), and recently, for predicting habitat suitability in mammalian conservation (McComb et al, 2021). This approach has the advantage of simplifying the experimental design, avoiding having to handle live animals in the laboratory, or to embark on costly fieldworks.…”

“…Later, a number of authors have applied them for predicting a variety of contexts (e.g., climatic impact on species range: Huey et al, 2012;Kearney et al, 2009; heat loss and behavioral thermoregulation in endotherms: Kenagy et al, 2002;McCafferty et al, 2011; reconstructing dinosaur physiology Seebacher, 2003), and recently, for predicting habitat suitability in mammalian conservation (McComb et al, 2021). This approach has the advantage of simplifying the experimental design, avoiding having to handle live animals in the laboratory, or to embark on costly fieldworks.…”

Relationship between body weight and elevation in Leadbeater’s possum (

“…No possums included in this study used natural hollows; instead, all possums were captured from artificial nest boxes during the day. This was an important variable to control as temperatures inside nest boxes are known to fluctuate more than inside naturally occurring hollows (Rowland et al 2017;McComb et al 2021), potentially making it more difficult for the animals using them to remain within their thermo-neutral zone (Hardy and DuBois 1937;Rubner 1982;IUPS Thermal Commission 2001). Extended exposure to temperatures outside this zone increases an individual's thermoregulatory energy requirements and may have significant impacts on body size (Lovegrove 2005).…”