Tools and Technology Quantifying Relative Levels of Solar Radiation at Bat Roosts Using Pyranometers KRISTIN J. BONDO, 1,2 University of Regina, Department of Biology, 3737 Wascana Parkway, Regina, SK S4S 0A2, Canada DAVID R. BROOKS, Institute for Earth Science Research and Education, 2686 Overhill Drive, Eagleville, PA 19403, USA R. MARK BRIGHAM, University of Regina, Department of Biology, 3737 Wascana Parkway, Regina, SK S4S 0A2, Canada ABSTRACT Although the amount of solar radiation received at roost sites used by bats has been speculated to be a factor driving roost-site selection and roost switching behavior, few studies have scientifically quantified and recorded it over time. We demonstrated through a field test how silicon-cell pyranometers, which are commonly connected to dataloggers and used in atmospheric studies to measure solar irradiance on a planar surface, can also be used to measure and record relative solar radiation levels at roost trees used by bats and other wildlife. Using commercially available pyranometers might not be feasible for many wildlife studies because they are expensive; we demonstrate how they can be built relatively simply and inexpensively, and calibrated with a commercial silicon-cell pyranometer. Ó 2017 The Wildlife Society. KEY WORDS bat, cavity, Eptesicus fuscus, pyranometer, roost, Saskatchewan, solar radiation, tree. For many animals, microclimate is an important determinate influencing the location of shelter. This is especially true for small endotherms that have a high surface area-to-volume ratio and require relatively high energy to maintain elevated body temperatures (Schmidt-Nielson 1997). Small species such as bats, hummingbirds, rodents, and shrews select shelter (often referred to as roosts) based on microclimate for periods they will be inactive (Calder 1973, Schmidt-Nielson 1997). A meta-analysis and reviews on forest-roosting bats found that temperate bats used roost trees that were taller, had larger diameters, and in areas of more open canopy and greater snag density than other trees in the forest (Hayes 2003, Kalcounis- R€ uppell et al. 2005, Brigham 2007). Large, tall trees that extend high above the canopy may be selected by bats because they are surrounded by few other trees and receive more solar radiation, thus providing warmer thermal regimes (Waldien et al. 2000, Ruczynski 2006). Bats may switch roosts in response to changing microclimates (Kerth et al. 2001, Bartonicka and  Rehak 2007). Previous research postulates that roost structures that receive increased amounts of solar radiation will facilitate growth and development of juveniles in maternity roosts (Crampton and Barclay 1998, Foster and Kurta 1999). Although the amount of solar radiation received has been suggested to influence roost selection by forest-roosting bats, we are unaware of any studies that have quantified and recorded solar radiation received at roosts over time. Our objectives were to 1) determine whether inexpensive self- built silicon-cell pyranometers, which are used to measure solar irradiance on a planar surface, can be connected to dataloggers and used to measure and record relative solar radiation levels at roost trees used by bats and other wildlife and 2) describe how these devices can be built and calibrated with a commercial pyranometer for a fraction of the cost of commercial versions. STUDY AREA We used pyranometers to measure solar radiation at roost trees used by bats from July to August 2007 and from June to August 2008 in the West Block of Cypress Hills Inter-Provincial Park (49834 0 N, 109853 0 W), Saskatchewan, Canada, and on nearby private property. Permission was granted by the park and the landowner to access and climb trees on their property. In Cypress Hills and on the neighboring property, maternity groups of big brown bats (Eptesicus fuscus) roosted in cavities in living and dead trembling aspen (Populus tremuloides) trees infected with heart-rot. They gained access to cavities through entrance holes that were either created naturally or excavated by woodpeckers, including the northern flicker (Colaptes auratus) and red-naped sapsucker (Sphyrapicus nuchalis). Previous research recorded the precise locations of roost trees used by maternity colonies of big brown bats in the area from 1993–2008 (Kalcounis and Brigham 1998, Willis and Brigham 2004, Metheny et al. 2008). METHODS We constructed silicon-cell pyranometers based on educa- tional research pyranometer kits and assembly instructions Received: 1 July 2016; Accepted: 23 February 2017 1 E-mail: kristin.bondo@ucalgary.ca 2 Present Address: Department of Ecosystem and Public Health, University of Calgary, 3280 Hospital Dr. N.W., Calgary, AB T2N 4Z6, Canada. Wildlife Society Bulletin; DOI: 10.1002/wsb.766 Bondo et al.  Technique Measuring Solar Radiation at Roosts 1