In artificial roost comparison, bats show preference for rocket box style

Abstract

Understanding microhabitat preferences of animals is critical for effective conservation, especially for temperate-zone bats, which receive fitness benefits from selecting optimal roost microhabitats. Artificial roost structures are increasingly being used in conservation efforts for at-risk bat species. To evaluate microhabitat differences in common artificial roost structures and determine if roost selection occurs based on structure type, we installed artificial roosts of three different styles (bat box, rocket box, and bark mimic) in six clusters. We compared size and measured temperature parameters (12 points/roost) while bats were excluded from one cluster. We simultaneously conducted census counts during the active season at five more clusters open to bats for 1–2 years. The rocket box style provided larger entrance area, surface area, and volume versus other roost types. Microclimate varied with roost design. More positions inside the bat box and rocket box stayed within critical temperature limits for bats (0–45°C)—i.e., were usable. The bark-mimic provided less usable space than the rocket box and, often, large proportions of the roost were > 45°C. The rocket box provided the widest temperature availability in a given hour (max range available 7°C) and was more stable than the bark mimic. A maternity colony of Indiana bats (Myotis sodalis) selected the rocket box style; four of five available rocket boxes became primary maternity roosts, with 2–210 bats emerging per night. Future work should aim to manipulate roost size, temperature availability, and temperature stability in isolation to identify which features drive roost microhabitat selection by bats. Comparative studies of artificial roosts account for some inherent irregularity in natural systems, allowing us to study the dynamics of roost microhabitats. We recommend season-long monitoring of microhabitat in novel artificial refuges and comparative studies of artificial and natural roosts, and urge managers to consider potential positive and negative effects when substituting artificial roosts for natural habitat.

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

“…Currently, we lack detailed microclimate profiles for most bat box designs, but several studies have documented temperatures >40°C (maximum roost temperature: >40°C, Bartonička & Řehák, 2007; >50°C, Bideguren et al, 2018; 53°C, Brittingham & Williams, 2000; 54.5°C, Flaquer et al, 2014; 53°C, Griffiths, Rowland, et al, 2017; 61°C for a bark mimic roost, Hoeh, Bakken, Mitchell, & O'Keefe, 2018; >40°C, Kerth, Weissmann, & König, 2001; >50°C, Lourenço & Palmeirim, 2004; 54°C, Tillman, 2019), highlighting that many bat box designs could subject bats to heat stress. Exacerbating this, most published research has focused on novel box designs or modifications, providing data that are less applicable to practitioners and homeowners who are not intent on building or modifying their own boxes.…”

Using mounting, orientation, and design to improve bat box thermodynamics in a northern temperate environment

“…In Portugal, temperatures of artificial roosts painted black (vs. white or gray) were most comparable to building roosts and had the highest use by bats 42 . In the USA, the “rocket” box, which was the largest roost, remained within the critical temperature thresholds the greatest proportion of time 67 . In Australia 68 , found that bat box colour, chamber sequence, construction materials, and vents influenced internal temperatures.…”

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

“…The localised cooling effect in the lower section of the chamber was likely due to the chamber's vent. A previous study conducted in the Midwest region of the USA also documented temperature differences within boxes [61]. They found that two of their box designs could differ by more than 10 • C between upper and lower portions of the boxes during warm and clear days.…”

“…It is unclear if short durations of temperatures over 40.0 • C are detrimental to bats [50,51,66] and likely varies between species and location [19,49]. Some bat box studies conducted in warm climates have raised concerns that bat boxes become lethal during hot ambient conditions [41,56], with Hoeh et al [61] recording box temperatures of up to 61 • C. The data obtained in this study indicates that at the study site, box temperatures experienced in black boxes (with an afternoon sun aspect) installed on poles with a natural groundcover underneath, were suitable for bats on an average summer day (mean maximum: 29.7 • C). However, during spells of very hot ambient temperatures or in climates experiencing warmer ambient temperatures to that at the study site, the availability of box designs buffering from very hot ambient temperatures and providing a thermal gradient are important.…”