Which components of diet quality affect retention time of digesta in seabirds?

Abstract

1. The nature of the diet can affect the gut retention time of food consumed by an animal, and a theoretical framework has been developed to explain this in terms of optimal digestion rates. However, diets may differ in a number of different attributes, all of which may separately affect the optimal length of time that they are retained in the gut. 2. Here an attempt is made to elucidate which of these features are important in determining gut retention time of different fish species when fed to nine north Atlantic seabird species, and discuss the different potential optimization criteria for retention time in seabirds. 3. Retention times of Lesser Sandeel (Ammodytes marinus Raitt.) were shortest, and this species was also rapidly broken down in vitro. Sprat (Sprattus sprattus (L.)) took longer to be broken down in vitro than Whiting (Merlangius merlangus (L.)), and also had a high energy and lipid content, which might be expected to result in slow digestion; yet retention times of the two species were similar. 4. Meal size also had an important effect on gut retention times, large meals being retained for longer in the gut than small meals, apparently because of an upper limit on the peak excretion rate. 5. Diet and meal‐size related characteristics are important factors influencing prey profitability, prey selection and foraging patterns in seabirds.