Jan A. van Gils, Bernard Spaans, Anne Dekinga, and Theunis Piersma. 2006. Foraging in a tidally structured environment by red knots (Calidris canutus): ideal, but not free. Ecology 87:1189–1202.

Appendix C. On the calculation of risk of predation μ_is.

Risk of predation μ_is over a 50-min time step depends on the action i taken (resting or feeding) and on the gross intake rate b_is obtained (which in turn depends on i (obviously b_is = 0 when i = rest) and on current location s). When the bird decides to rest (i = rest), then μ_is = μ_non-foraging (Fig. C1). When the bird decides to feed (i = feed), then μ_is = μ_foraging in case gross intake rate b_is is not constrained by rate of digestion in the gut  (given by Kvist and Lindström 2003), i.e., when b_is < . In case gross intake rate is constrained by rate of digestion, i.e. when b_is ≥ , the proportion of time actively foraging is given by / b_is (i.e., when averaged over the full 50-min interval b_is =  ), hence μ_is = μ_non-foraging+  (μ_foraging-μ_non-foraging).

FIG. C1. Risk of predation μis as a function of the proportion of time actively foraging.

LITERATURE CITED

Kvist, A., and Å. Lindström. 2003. Gluttony in migratory waders – unprecedented energy assimilation rates in vertebrates. Oikos 103:397–402.