Variation in Summer and Winter Microclimate in Multi-Chambered Bat Boxes in Eastern Australia: Potential Eco-Physiological Implications for Bats

Niels Rueegger

doi:10.3390/environments6020013

Abstract

Bat boxes are commonly used as a conservation tool. Detailed knowledge on the influence of box elements on microclimate is lacking, despite eco-physiological implications for bats. Summer and winter box temperature and relative humidity patterns were studied in narrow multi-chambered plywood and wood-cement boxes in eastern Australia. Box exteriors were black or white and plywood boxes comprised vents. Relative humidity was higher in white boxes than black boxes and box colour, construction material, chamber sequence and vents influenced temperatures. Maximum box temperature differences between designs varied by up to 9.0 °C in summer and 8.5 °C in winter. The black plywood box consistently recorded the warmest temperatures. This design comprised a temperature gradient between chambers and within the front chamber (influenced by vent). During the 32-day summer sampling period, the front chamber rarely recorded temperatures over 40.0 °C (postulated upper thermal tolerance limit of bats), while the third and fourth chamber never reached this threshold. At the study site, the tested black boxes are considered most thermally suitable for bats during average summer conditions. However, during temperature extremes black boxes likely become too hot. Wood-cement, a durable material not previously tested in Australia should be considered as an alternative construction material.

Highlights

Microhabitat selection can be critical for small-bodied animals [1,2]
The climate experienced at the site during the monitoring of the box microclimates was warm during summer 2015 and relatively cool during winter 2014
During the day-period, white boxboxes temperatures followed ambient temperatures closely, whereas the temperatures of the black temperatures followed ambient temperatures closely, whereas the temperatures of the black boxes were warmer than the white boxes and ambient temperatures (Figure 2)

Summary

Introduction

Microhabitat selection can be critical for small-bodied animals [1,2]. One animal group where microclimate is central to their life cycle is echolocating bats, with many species using tree cavities for roosting [11]. Few studies have been conducted on microclimate roost selection by heterothermic tree-cavity roosting bats. Studies reported the selection of thermally unstable roost sites and roosts that allowed for passive rewarming [12,13]. During the maternity season, energy requirements of females are likely to be high due to milk production, so roost temperatures close to or within the TNZ may be favoured to maintain normothermia and facilitate the growth of young [14,15,16]. Studies on artificial roosts using bat boxes in the Northern

Objectives

Methods

Results

Conclusion