δ13Ccorri = (δ13Ci - δ13Cinv )/CRinv
where δ13Ccorri is the corrected carbon isotopic ratio for individual i, δ13Ci is the carbon isotopic ratio for individual i, δ13Cinv is the average carbon isotope ratio of macroinvertebrates and CRinv is the carbon range (δ13Cmax − δ13Cmin) of macroinvertebrates. δ13Ccorri is hereafter used as an indicator of reliance on terrestrial prey (i.e., increasing value suggests increasing reliance of an individual on terrestrial prey).