CENSUSING TAWNY OWLS STRIX-ALUCO BY THE USE OF IMITATION CALLS

Tawny Owls respond well to imitation or playback of conspecific calls. In 94% of known territories a response to imitation was obtained within 30 min. No measured temporal or weather variable had any effect on response time. The only factor that appeared to influence response time was population density, with birds in open farmland responding faster and more vigorously than those in continuous woodland. This is considered to be due to lack of exposure to other owls in open farmland. Female owls respond more to imitated male calls in autumn than in winter and spring. This may be due to the fact that autumn is when pair formation occurs, and females may be investigating new males. Alternatively they may be defending their territory at a time when juveniles are searching for vacancies. The findings suggest that censusing should be conducted for 30 min, at any time throughout the winter and in any reasonable weather conditions.