Roofvogels in de Nederlandse wetlands VI : Energie opname en groei van nestjongen van de bruine kiekendief Circus aeruginosus#een functionele verklaring voor afwijkende sex ratiosa

The questions in this study are: 1. Do female Marsh Harrier nestlings have a higher total food intake than their male siblings? The hypothesis postulated here is: the larger than 50% sex ratio in Marsh Harrier populations results from the fact that female nestlings have a higher energy requirement than male nestlings. In order to anser this question, the food intake of 13 hand-reared Marsh Harrier nestlings of both sexes was measured; 2. What is the energy budget of male and female Marsh Harrier nestlings? Gross and metabolizable energy intake of the nestlings were established. The energy expenditure was estimated by means of respirometry; 3. Does the doubly labeled water technique give a correct estimate of the energy expenditure in growing Marsh Harrier nestlings? Estimates of energy expenditure obtained by respirometry are compared with estimates acquired with the DLW technique. Study areas were Flevoland and the Lauwersmeer.