Only recently in their evolution have Little Owls encountered man-made nest sites in which overheating (temperatures above 40° C) threatens the survival of embryos and chicks. Little Owls may not yet be able to distinguish save nest locations from those that are likely to overheat. Here, we selected a variety of Little Owl nest sites to monitor the occurrence of overheating. At potential breeding sites, winter temperatures were measured to investigate whether these could be used by the owls to predict the likelihood of overheating in the breeding season. Nest sites that were sun exposed and/or had little ventilation were prone to overheating, in contrast to shaded and well ventilated locations. Roof cavity temperatures showed a different trend with tree cavity temperature in winter and spring, misinforming the owls about the safety of potential future nesting sites.