Nest box design for a changing climate: The value of improved insulation

Abstract

Summary Mean air temperatures and the frequency, intensity and duration of extreme weather events such as heatwaves are increasing due to climate change. Nest boxes experience more variable and extreme temperatures than natural cavities, which may reduce survival and reproductive success of the species which utilize them, but little is known about the factors which drive nest box temperature profiles. We quantified the potential for retrofitted insulation on nest boxes to modify internal temperatures and to mimic the thermal characteristics of natural cavities more closely. We tested three types of materials with insulative or reflective properties which were easy to retrofit to nest boxes: 3‐cm‐thick polystyrene, pleated foil batts and reflective paint. We found that polystyrene and foil batts reduced mean nest box temperatures during the day by 0.31 ± 0.01°C and 0.17 ± 0.01°C, respectively (but up to 5.84°C and 4.02°C). The effects of all insulation types were dependent on the time of day, and only polystyrene had a significant effect at night, with a greater capacity to retain heat (mean 0.21 ± 0.01°C warmer). Contrary to expectations, reflective paint caused a small increase in temperature during the late afternoon. In our study, the temperature modulation provided by insulation was able to match or exceed that due to variation in nest location and surrounding vegetation canopy cover. Our findings show that polystyrene and foil batts may offer effective and tractable means to mitigate the effects of extreme temperatures in nest boxes and thereby help achieve temperature profiles more similar to natural cavities.

Avoiding a conservation pitfall: Considering the risks of unsuitably hot bat boxes

“…The dangers to bats from climate change are manifold; in addition to heat stress, changes in phenology, physiology, and distribution can be expected (Jones & Rebelo, 2013). With 2019 being the second warmest year on record (mean global temperature anomaly of +0.95°C above average; NOAA, 2020), temperatures expected to increase 0.4–2.6°C by mid‐century (IPCC, 2014), and heat waves expected to increase in frequency, intensity, and duration (Meehl & Tebaldi, 2004), overheating events in bat boxes may become more common (Bideguren et al, 2018; Larson, Eastwood, Buchanan, Bennett, & Berg, 2018). Currently, we lack empirical research on the impacts of climate change on bat box designs and deployment strategies (but see Bideguren et al, 2018; Larson et al, 2018).…”

“…For example, Doty, Stawski, Currie, and Geiser (2016) found maximum temperatures in white, single‐chamber bat boxes were 7.5°C cooler than in black bat boxes; notably, however, bats preferentially selected black bat boxes in their wintertime study, likely due to the thermal benefits of a warmer microclimate (Wilcox & Willis, 2016). Using dense construction materials with low thermal conductance could also reduce overheating risk (Bideguren et al, 2018) and lead to more stable microclimates (Larson et al, 2018). For example, black, four‐chambered bat boxes made of wood‐cement (a molded mixture of wood shavings and cement) buffered high temperatures better than an identical design made out of plywood; the wood‐cement design was up to 3.2°C cooler during the summer (Rueegger, 2019).…”

Breeding birds actively modify the initial microclimate of occupied tree cavities

“…These findings were in stark contrast to the expectations of greater heat retention in tree cavities that insulate most efficiently. Such expectations were based on observations from nest boxes, where those with improved insulation resulted in a greater internal temperature increase in response to an artificial heat source within, compared to those nest boxes without additional insulation (Kearney et al 2011;Larson et al 2018). Following installation of heat pads, Grüebler et al (2014) recorded only a slightly greater temperature increase in empty tree cavities compared to nest boxes, which insulated less effectively.…”

“…Moreover, the amount of heat generated by endothermic animals and retained inside cavities might differ between sites, with presumably greater amount of heat retained in those that insulate more efficiently, i.e. more effectively reduce heat loss from inside (Kearney et al 2011;Larson et al 2018). Thus, the microclimate of occupied cavities might depend on a combination of ambient temperature, cavity insulation and the heating activity of endothermic occupants.…”

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

“…This study indicated that: white boxes, box materials that buffer warm ambient temperature (e.g., wood-cement over plywood) and box designs that comprise a temperature gradient within the box (e.g., multiple chambers with vents) can negate hot ambient temperature to some extent. Consideration of these box design elements and identifying other design elements to further improve the buffering capacity from extreme heat [56,67] may be particularly important given the predicted climate warming and increased periods of extreme heat [68].…”