Nestlings of aerial insectivores adjust their energetics, behavior, and development of internal organs in response to food shortages and subsequent improvements in feeding conditions. Here, we present results of laboratory refeeding of Bank Swallow (Riparia riparia) nestlings, which were undernourished between 4 and 7 days of age. During a subsequent three-day-long refeeding, their body mass did not catch up with that of individuals continuously fed ad libitum. However, refed young managed to compensate for delayed growth of pectoral muscles, small intestines, and fully restored fat reserves. Their resting metabolic rates and body temperatures increased to values similar to those of nestlings fed ad libitum. In contrast, digestive activity of their guts (quantified as carrier-mediated intestinal brushborder uptake rate of L-proline) was reduced, as compared with the period of undernutrition. Likewise, high locomotor activity observed during food shortage was significantly reduced upon refeeding. Furthermore, differences in body mass between nest mates, which had earlier modulated both locomotor activity and physiological responses to food shortage, had no effect on mobility and physiology of refed nestlings. Our results indicate that even a short, three-day period of refeeding triggered conspicuous acceleration of growth and development of vital internal organs in previously undernourished nestlings. However, that was not accompanied by significant compensatory whole-body growth (defined as a period of above-normal rapid growth, relative to age).
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Vol. 121 • No. 4