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The effects of diet switching and mixing on digestion in seabirds
Hilton, G.M., Furness, R.W., & Houston, D.C. (2000) Functional Ecol. 14(2):145-154
1. Animals modulate digestive function in order to optimize digestion of their current diet. Two seabird species were used to test the idea that, as a result, changing and mixed diets might adversely affect digestive performance.

2. When switched from an energy-dense fish diet (Sprat, Sprattus sprattus (L.)) to an energy-dilute diet (Whiting, Merlangius merlangius (L.)), Lesser Black-backed Gulls, Larus fuscus L. had a worse digestive performance than birds that were acclimated to Whiting, indicating a cost of diet switching. However, when switched from Whiting to Sprat, Lesser Black-backed Gulls had better digestive performance than birds acclimated to the Sprat diet.

3. When switched from a Whiting to a Sprat diet some Common Guillemots, Uria aalge (Pont.), developed diarrhoea, although after acclimation birds were able to digest Sprat normally.

4. Common Guillemots, but not Lesser Black-backed Gulls, showed a reduction in digestive efficiency when given both diets in a mixed meal.

5. Common Guillemots appear to have a less flexible digestive system than Lesser Black-backed Gulls. This difference in response of the two species may be related to differences in their ecology.

6. Subtle diet shifts may affect digestive performance of animals, and therefore digestive effects, as well as factors such as prey availability and ease of capture, might affect food choice.

Keywords: Digestion rate, digestive efficiency, Larus fuscus, retention time, Uria aalge


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