Early Growth and Development of the Common Barn-Owl's Facial Ruff

Abstract

Abstract The ability of the Common Barn-Owl (Tyto alba) to localize sounds produced by potential prey can be explained on the basis of sensitivity to differences in interaural time and intensity. The size of the owl's head is a prime determinant of interaural time differences, whereas the facial ruff is the prime determinant of interaural intensity differences. During the 60 days following hatching, the physical structures that establish these binaural cues undergo massive growth. Barn-owl chicks are altricial and scantily feathered when they hatch. Growth of the head and ruff feathers occur at separate times during early maturation. Between 11 and 30 days after hatching, the diameter of the head approximately doubles. Between 35 and 60 days, facial ruff feathers emerge and grow to nearly adult length (ca. 20 mm). During the first 60 days of life, the barn-owl auditory system would be subject to widely varying binaural cues which eventually stabilize.