Tips for making bat boxes safer for bats

Roost cluster for research study in Indiana, Photo by Joy O’Keefe

Decreasing overheating risk

  • Avoid dark-colored bat boxes as dark colors substantially increase overheating [1,2] and bats may preferentially select dark-colored boxes [3–5], which increases the risk.
  • We recommend lighter colors (than have traditionally been recommended) as light colors absorb less solar radiation and will be cooler, thus decreasing overheating risk [1,6].
  • High solar exposure can increase bat box temperature and increase overheating risk [1,4,7]. Because bats maternal bats typically select solar exposed bat houses over shaded alternatives [8,9], we recommend that boxes be placed so that they receive some shade during the hottest part of the day.
  • Small bat houses with low mass may overheat more readily and not offer bats saftey from high temperatures [10,11]. We recommend tall bat houses with four sides as these structures provide large temperature gradients [7,12,13], which allows bats to move to avoid high temperatures.
  • We recommend larger bat boxes for bat species that form larger groups. If a larger group forms in a small bat box, there likely will not be room for some individuals to move down and, thus, bats at the top may be exposed to lethally hot temperatures.
  • We also recommend larger bat boxes made of dense materials with low thermal conductance as they will have a higher thermal mass and thus take longer to heat [2,6].
  • Adding insulating layers is also a good method to reduce bat box temperatures [14].
  • Adding extra vents to your bat box will reduce overheating risk and make the roost cooler for bats [2,13].
  • Adding additional shading features (e.g., large or elevated roof) to your bat house can also reduce overheating risk [13,15].

References

1.        Griffiths SR, Rowland JA, Briscoe NJ, Lentini PE, Handasyde K, Lumsden LF, et al. Surface reflectance drives nest box temperature profiles and thermal suitability for target wildlife. PLoS One. 2017;12: 1–22. doi:10.1371/journal.pone.0176951

2.        Bideguren MG, López-Baucells A, Puig-Montserrat X, Mas M, Porres X, Flaquer C. Bat boxes and climate change: testing the risk of over-heating in the Mediterranean region. Biodivers Conserv. 2018. doi:10.1007/s10531-018-1634-7

3.        Doty AC, Stawski C, Currie SE, Geiser F. Black or white? Physiological implications of roost colour and choice in a microbat. J Therm Biol. 2016;60: 162–170. doi:10.1016/j.jtherbio.2016.07.015

4.        Kerth G, Weissmann K, König B. Day roost selection in female Bechstein’s bats (Myotis bechsteinii): A field experiment to determine the influence of roost temperature. Oecologia. 2001;126: 1–9. doi:10.1007/s004420000489

5.        Lourenço SI, Palmeirim JM. Influence of temperature in roost selection by Pipistrellus pygmaeus (Chiroptera): Relevance for the design of bat boxes. Biol Conserv. 2004;119: 237–243. doi:10.1016/j.biocon.2003.11.006

6.        Rueegger N. Variation in summer and winter microclimate in multi-chambered bat boxes in eastern Australia: potential eco-physiological implications for bats. Environments. 2019;6: 1–19. doi:10.3390/environments6020013

7.        Crawford RD. Bat boxes as mitigation tools: Factors impacting microclimate and Myotis sodalis roost seletion. Eastern Kentucky Universty. 2020.

8.        Brittingham MC, Williams LM. Bat boxes as alternative roosts for displaced bat maternity colonies. Wildl Soc Bull. 2000;28: 197–207. doi:10.2307/4617303

9.        Whitaker JO, Sparks DW, Brack V. Use of artificial roost structures by bats at the Indianapolis International Airport. Environ Manage. 2006;38: 28–36. doi:10.1007/s00267-005-0117-2

10.      Flaquer C, Puig-Montserrat X, López-Baucells A, Torre I, Freixas L, Mas M, et al. Could overheating turn bat boxes into death traps? Barbastella. 2014;7: 46–53. doi:10.14709/BarbJ.7.1.2014.08

11.      Rowland JA, Briscoe NJ, Handasyde KA. Comparing the thermal suitability of nest-boxes and tree-hollows for the conservation-management of arboreal marsupials. Biol Conserv. 2017;209: 341–348. doi:10.1016/j.biocon.2017.02.006

12.      Hoeh JPS, Bakken GS, Mitchell WA, O’Keefe JM. In artificial roost comparison, bats show preference for rocket box style. PLoS One. 2018;13: 1–16. doi:10.1371/journal.pone.0205701

13.      Tillman FE. Bat box design affects microclimate and suitability as habitat. M.S. Thesis. Indiana State University. 2019.

14.      Larson ER, Eastwood JR, Buchanan KL, Bennett ATD, Berg ML. Nest box design for a changing climate: The value of improved insulation. Ecol Manag Restor. 2018;19: 39–48. doi:10.1111/emr.12292

15.      Alcalde JT, Martínez I, Zaldua A, Antón I. Conservation of breeding colonies of cave-dwelling bats using man-made roosts. Barbastella. 2017;10.

Clay roost in Catalonia, Photo by Joy O’Keefe