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. 2018 Oct 31;13(10):e0205701.
doi: 10.1371/journal.pone.0205701. eCollection 2018.

In Artificial Roost Comparison, Bats Show Preference for Rocket Box Style

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Free PMC article

In Artificial Roost Comparison, Bats Show Preference for Rocket Box Style

Julia P S Hoeh et al. PLoS One. .
Free PMC article

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.

Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Photo of clustered roosts and map of roost clusters installed at site.
(A) One of six artificial roost clusters installed near Plainfield, IN. Each cluster contained one bark mimic (left), one rocket box (center), and one bat box (right) placed 2 m apart and randomly installed in a west to east line. (B) Map of roost clusters; dark gray indicates the roosts in this cluster were open to bat use, light gray indicates bats were excluded from roosts in the cluster for detailed temperature recording. Clusters 30, 40, and 50 were installed in 2015 and clusters 20, 60, and 70 were installed in 2016.
Fig 2
Fig 2. Two-day sample of temperatures recorded at each of 12 positions in artificial roosts.
Weather station air temperature (black) recorded for two days in 2016 (29 June and 4 July), and same-day temperatures recorded by each of the iButton thermochrons in the bat box, rocket box, and bark mimic. Bats were excluded during temperature recording at this cluster of roosts in Plainfield, IN.
Fig 3
Fig 3. Temperatures recorded on sample cool and warm days, and portion of roost usable based on temperature data.
Data loggers recorded temperature at three heights (top, middle, or bottom) and at four intercardinal directions (southeast, southwest, northwest, and northeast), as illustrated by the 12 sections for each roost (A and B). The data logger failed in the middle northeast of the bark-mimic roost. (A) Cool day example (16 May 2016) indicating minimum daily temperature recorded. (B) Warm day example (12 June 2016) indicating maximum daily temperature recorded. (C) Percent of cool days (mean air temperature < 10°C, n = 20 days) when portions of each roost type were ≤ 0°C and considered not usable. (D) Percent of warm days (mean air temperature ≥ 10°C, n = 151 days) when portions of each roost type were ≥ 45°C and considered not usable. Data collected at three adjacent artificial roosts from which bats were excluded, near Plainfield, IN, 21 March–7 September 2016.
Fig 4
Fig 4. Interaction plots for predictor variables that significantly interacted with box type, with regression lines and 95% confidence intervals based on those interactions.
(A) Roost temperature availability increased significantly with air temperature daily range (Trange) and interacted with roost type (S2 Table). (B) Variability significantly decreased with increasing daily percent cloud cover, but this varied by roost type (S3 Table). Data collected from three adjacent artificial roosts from which bats were excluded, near Plainfield, IN.

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Grant support

The Indianapolis Airport Authority (https://www.indianapolisairport.com; Grant to JO), Indiana Space Grant Consortium (https://insgc.spacegrant.org; Grant to JH), Indiana State University (indstate.edu; Grant to JH), and Hendricks County Parks (http://hendrickscountyparks.org; Grant to JO) funded this study. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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