Digestive bottleneck affects foraging decisions in red knots Calidris canutus. II. Patch choice and length of working day

When prey occur at high densities, energy assimilation rates are generally constrained by rates of digestion rather than by rates of collection (i.e. search and handle). As predators usually select patches containing high prey densities, rates of digestion will play an important role in the foraging ecology of a species. The red knot Calidris canutus shows tremendous inter- and intra-individual variation in maximum rates of digestion due to variation in the size of the processing machinery (gizzard and intestine), which makes it a suitable species to study the effects of digestive processing rate on foraging decisions. Here we report on patch use, prey choice, and daily foraging times as a function of gizzard size in free-ranging, radio-marked, red knots. As knots crush their bulky bivalve prey in their gizzard, the size of this organ, which we measured using ultrasonography, determines digestive processing rate.

JAN A. VAN GILS, ANNE DEKINGA et al., Journal of Animal Ecology 74 (1), 120-130