Ardea
Official journal of the Netherlands Ornithologists' Union

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Zwarts L. & Blomert A.M. (1990) Selectivity of Whimbrels feeding on Fiddler Crabs explained by component specific digestibilities. ARDEA 78 (1-2): 193-208
Whimbrels feeding on crabs took food with a low rate of return because half of the mass was inorganic, and 30% of the organic mass within the skeleton itself was not digestible. The digestibility of this prey (65%) was therefore below the average efficiency with which birds usually digest fish or flesh. The Whimbrel is able to metabolize 99% of the fat, 74% of the protein (correcting for urinary nitrogen production) and 1% of the carbohydrates (found mainly in the skeleton). The apparent and true metabolizable energy content of crabs was 7 and 8 kJ g-1 dry mass, respectively. When more food was available, the bird became more selective by refusing a greater part of the skeleton. As a consequence, the relative amount of flesh in the food increased. Food digestibility decreased when more food was ingested per day. This was probably due to a third factor: intake rate increased with the amount of food taken and a higher intake rate reduced prey digestibility. However, since the decrease in digestibility was less than the increase in intake rate, ingesting food at the higher rate was a profitable strategy.


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