Young Eurasian Scops Owls make individually distinctive vocalizations

Abstract

Vocal distinctiveness is expected to occur more often in colonial-breeding species as the parents need to recognize their offspring in a large group of conspecifics. Territorial species like the Scops Owl are expected to exhibit low distinctiveness. Contrary to what was expected, spectrographic analysis of the food-begging calls of young Scops Owls revealed previously unknown, complex acoustic structure. Within recording sessions, call duration exhibited the highest repeatability (average R 0.82), followed by the peak frequency in the last third of the call (0.61). Other spectral measures showed low to moderate repeatability (0.32 - 0.57), while the time between subsequent calls was the least repeatable (0.15). When comparing recordings made on different nights, Linear Discriminant Analysis assigned 55.7% of the calls to the correct individual, and 73.1% when restricting analysis within broods. When analyzing variability across recordings, individuals explained most of the variation in Call duration and Peak frequency in the last third of the call (89.5 % and 81.2 %, respectively), while recordings explained little variation (3.4 % and 1.3 %, respectively), suggesting that those acoustic features were the most important in vocal stability and distinctiveness. The calculated information capacity HS was 4.48 bits, i.e. within the range of values found in loosely-colonial species. The results suggest that the vocalizations of young Scops Owls show moderate individuality that could only help offspring recognition among a small number of individuals. However, the functional significance of call distinctiveness remains unclear; a few hypotheses are discussed. Keywords: Acoustic signature, coloniality, fledglings, individuality, Otus scops, repeatability.