Estimating size of populations of bats during nocturnal emergence from caves relies on techniques of visual counting that are subjective and highly dependent on skill of the observer. A noninvasive technique, using thermal infrared-imaging and digital picture processing, was developed and tested at two caves in northern Alabama. A comparison of estimates between this technique and that of a skilled observer with a night-vision scope revealed a difference of <6%. This semi-automated technique and its applicability are discussed.