The development of daily rhythmicity in Barn Owls (Tyto alba)

The development of biorhythms is an important aspect of the dynamic interaction between the young animal and its environment. The study of such phenomena gives an insight into general evolutionary characteristics of development as well as into species-specific features. Biorhythms depend on a maturated intact central nervous system which works as a pacemaker and on fully developed sensory organs which give the synchronising input for the neuronal rhythm generator. While there is extensive knowledge of adult biorhythms, information on the ontogeny of such rhythms is limited. Video records of Barn Owl nestlings were analysed with regard to their development of rest/activity rhythms. Barn Owls are altricial birds; at birth they are nearly immobile, their eyes are closed and they are unable to feed by themselves. The analysis was made on nestlings of different age classes. At the age of 20 days the share of the 24h-period taken up by the locomotory activity of the nestlings was 11 - 13 %. A lot of ultradian rhythms were detected. They caused the typical polymodal pattern of the daily activity. In 30 day old nestlings the share of the 24h-span was 16 - 18 % and at the age of 45 days it was 20 - 22 %. This increase within the 24h-period is typical of the ontogeny of locomotory activity and is described in literature in mammals as well as in birds (Lumineau et al. 2001,Cousse et al., 1995).