Quality of cavity microclimate as a factor influencing selection of maternity roosts by a tree‐dwelling bat, Chalinolobus tuberculatus, in New Zealand

Abstract

Summary1. Cavity quality is important for the productivity and survival of many species of treedwelling wildlife. Intensive land management practices, such as logging and agriculture, frequently reduce cavity availability and potentially affect the long-term viability of populations. 2. The New Zealand long-tailed bat Chalinolobus tuberculatus selects roosts in small knot-hole cavities with specific structural properties relative to available cavities. They also change roosts daily among a large pool of different roosts. Such behaviour is likely to make C. tuberculatus vulnerable to human-induced deterioration in roosting habitat. 3. This study represents a case study of the degree of sophistication sometimes required to assess availability and quality of roost sites, by testing whether roosts selected by C. tuberculatus also have specific microclimates. 4. Selection for microclimate was demonstrated by comparing temperature and humidity inside unoccupied maternity roosts with available, apparently unused, knot-hole cavities, large trunk-hollows and ambient conditions. 5. Compared with ambient conditions, roost and available knot-hole cavities had stable microclimates displaying only small ranges in temperature and humidity. Temperature inside cavities was lower than ambient temperature in the day and was warmer (and peaked) at night. Humidity in cavities was constantly high. Mean temperatures within trunk-hollows (not known to be used by C. tuberculatus ) were cooler than mean ambient and roost temperatures, and temperature ranges in hollows were large and fluctuated similarly to ambient temperatures. 6. Compared with available cavities and hollows, roost cavities had higher minimum temperatures, and maximum temperatures occurred significantly later in the day and continued for significantly longer. Humidity ranges were less and high humidity was maintained for longer. 7. The results suggest that C. tuberculatus selects maternity roost sites with microclimatic conditions that are likely to accrue substantial energetic benefits. Predicted energy savings for adult bats using roost cavities compared with available knot-holes were 1·1-3·3%, and compared with hollows 3·4-7·3%. Greater energy savings would occur at night and benefit non-volant young. 8. In order to evaluate adequately and mitigate the full impacts of land-use practices, there is a need for wider tests to provide direct evidence of interactions between habitat management, cavity provision and survival of cavity-dependent wildlife.

Resting and nesting in a small mammal: sleeping sites as a limiting resource for female grey mouse lemurs

“…The observed preference for tree holes with thick walls and large volumes, both factors that increase the insulation capacities of tree holes (Kunz 1982;Sedgeley 2001;Gibbons & Lindenmayer 2002;Kunz & Lumsden 2003), further supports the hypothesis that thermoregulatory needs are largely responsible for the choice of sleeping site in the study animals. Furthermore, mouse lemurs have only been observed to enter torpor during the dry but not the wet season (Schmid & Speakman 2000).…”

“…Ardia et al 2006;Velky et al 2010). It is well documented that tree holes can buffer against temperature fluctuations (Schmid 1998;Sedgeley 2001;Willis & Brigham 2007;Isaac et al 2008) and the change in sleeping site usage that we observed may thus indicate the lower thermoregulatory constraints experienced by the females during the wet season. During the dry season, the lower minimum temperatures, greater temperature fluctuations and low food availability mean that females must expend more energy to maintain a high body temperature.…”

“…At the same time, entrance height for these tree holes was markedly lower than for nests or open sites. It has been suggested for cavity-nesting birds and bats that the risk of predation decreases with increasing entrance heights (Sedgeley 2001;Fisher & Wiebe 2006). Similarly, there is evidence that tree holes experience lower temperatures when located at greater entrance heights (Isaac et al 2008) and thus allow for larger energy savings as the animals can remain heterothermic for longer periods.…”

“…Sleeping sites can provide substantial thermoregulatory benefits for an individual since they afford shelter from adverse weather conditions and buffer against variation in ambient temperature and humidity (Schmid 1998;Speakman et al 1999;Roper et al 2001;Sedgeley 2001;Gibbons & Lindenmayer 2002). This is particularly important for small mammals that experience high heat loss as a result of an unfavourable volume-to-surface ratio (SchmidtNielsen 1997).…”

The importance of exotic plantation forest for the New Zealand long-tailed bat (Chalinolobus tuberculatus)

“…For the long-tailed bat, which relies mainly on roosting trees (Sedgeley & O'Donnell 1999b), roost quality is lower in pastoral areas compared with that in native forests (Sedgeley & O'Donnell 2004), although the quality of roosts in plantations is currently unquantified and so cannot be compared. Declines in roost quality associated with logging and agriculture are likely to affect bats' reproductive success and survival by increasing energetic costs and diminishing long-term population viability (Sedgeley 2001). Past declines in native fauna, and specifically longtailed bats, have been associated with a reduction in forested habitat (O'Donnell 2000b).…”