Winter Starvation in Captive Common Barn-Owls: Bioenergetics during Refeeding

Abstract

The bioenergetics of eight captive Common Barn-Owls (Tyto alba alba) acclimated at 5-degrees-C were studied during the restoration of a 30% reduction in body mass following a period of total food deprivation. The eight-day period during which body mass was restored (Refeeding I) was compared with a five-day prefasting period (Feeding), corresponding to steady body mass and a six-day period (Refeeding II) of stabilization at a new steady state. Food was given ad libitum throughout the feeding periods. During Refeeding 1, the rate of increase in body mass (13.9 +/- SD of 1.0 g/24 h in females and 9.2 +/- 0.8 g/24 h in males) was close to the maximum value for growth of captive or wild owlets. It was achieved by a 1.63-fold increase in gross energy intake and daily metabolized energy, respectively, of 370 +/- 42 and 275 +/- 31 kJ/d during Feeding. In contrast to the clear increase in food assimilation efficiency observed in other species during refeeding, the high rate of energy intake and body mass restoration in the Common Barn-Owl was associated with only a slight increase in assimilation efficiencies: 52.0 +/- 2.2% versus 49.1 +/- 1.0% during Feeding for dry mass; and 75.5 +/- 1.1% versus 74.1 +/- 0.6% for energy. This slight increase could only be attributed to a reduction of the energy lost in pellet production (i.e. to a higher effectiveness in gastric digestion). The energetic cost of daily change in body mass was estimated in both sexes and both feeding periods, and appeared to be constant (10.8 +/- 1.1 kJ/g fresh body mass). Using this value, the part of the daily metabolized energy invested in the existence metabolism was calculated. After four days of refeeding, existence metabolism paradoxically appeared similar or even higher than before fasting, while the body mass was still lower than the initial value. Thus, in contrast to the laboratory rat (Rattus norvegicus) or humans, the Common Barn-Owl is unable to enhance restoration of body reserves by minimizing existence requirements when refed ad libitum after a period of starvation. This might be partly due to the maintenance of a high locomotor activity throughout starvation and refeeding.