GROWTH AND FOOD REQUIREMENT FLEXIBILITY IN CAPTIVE CHICKS OF THE EUROPEAN BARN OWL (TYTO-ALBA)

The growth and the food requirements of the European barn owl (Tyto al ba) were studied in three groups of captive chicks. One group of chick s, raised in ad libitum food conditions by their parents, was used to measure body mass and linear growth of a number of structural body com ponents at their characteristic growth rate. A second group of chicks, hand-raised with food ad libitum until hedging, was used to measure f ood requirement at the characteristic growth rate. A third group, hand -raised with restricted feeding, was used to specify the plasticity of growth and food requirements still compatible with a normal developme nt at fledging. Chicks of both sexes of the first two groups experienc ed an overshoot in body mass (maximum of 391 g) when approximately 40 days old, followed by a decrease (to a mass of 314 g) until fledging a t 60 days old, giving a mass distribution with age in the form of a be ll-shaped curve. The daily food intake also showed a bell-shaped curve with a peak value of 80 +/- 10 g of fresh mice/day when the body mass was maximum. The decrease of food intake preceding fledging was spont aneous. The average daily food intake was 67 +/- 17 g/day between the ages of 20 and 60 days. In the restricted feeding group, however, the same timing for linear growth and hedging was achieved with a 17% redu ction of daily food intake. For the same fledging body mass as the ad libitum fed group, there was a flattening of the body mass curve. The significance of the overshoot in body mass and food intake is discusse d in terms of the chick's and brood's advantages and in terms of paren tal investment in this species with hatching asynchrony.