Hawaiian hoary bats (Lasiurus cinereus semotus) were captured at multiple locations on the east side of Hawaii Island from May 2018 through September 2019. Radio transmitters were affixed to captured bats and, when possible, radio telemetry was used to locate bats in trees used for day-roosts. Detection trials for roosting bats were conducted from June to October 2019. Bats confirmed as present at roosts were used as “targets” to evaluate the efficacy of detecting bats with thermal imaging, and when not effective (i.e., during hotter parts of the day when the technique could not discern bats from warm vegetation), visual searching with binoculars was also investigated. Most bat detection trials (48 of 95; 51%) were limited to searches of a single tree. The remaining trials involved searches of stands composed of 2 to 5 trees. Bats were detected in 30 of 95 (32%) trials. The time spent to detect a roosting bat ranged from 2 to 40 minutes (mean = 15 minutes). The height of a roost where bats were detected ranged from 4 to 24 m (mean = 16.8 m). Thermal imaging was used in 64 of 95 trials, of which 25 resulted in bat detection (40%). In contrast, thermal imaging was not used in 31 of 95 trials, of which 5 resulted in bat detection (16%). For trials where thermal imaging was used within 1 hour of sunrise, bats were detected in 15 of 27 trials (56%), whereas for trials conducted more than 1 hour past sunrise, bats were detected in 10 of 37 trials (27%). For bats at roost heights ≤15 m, use of thermal imaging detected bats in 10 of 23 trials (43%). For bats at roost heights >15 m, use of thermal imaging detected bats in 15 of 19 trials (79%). Bats were detected in 8 of 20 trials (40%) in trees or stands comprised of Eucalyptus species. Bats were detected in 22 of 75 trials (40%) in stands comprised of all other species besides Eucalyptus species. When bats were visually confirmed before the trial, 26 of 41 trials (63%) resulted in bat detection. Bats were detected in 9 of 31 trials (29%) conducted during periods of clear skies or few clouds. During cloudy, partly cloudy or periods with light rain, bats were detected in 21 of 64 trials (33%).