Table 2. Performance of logistic regression models at predicting presence of a breeding Wood Thrush at a study site, given either the biomass of calcium-rich prey, without slugs, or the biomass of myriapods. The measures of performance are based on the confusion matrices tabulating actual and predicted presences (Guisan and Zimmermann 2000). Cohen’s Kappa measures the improvement in number of correct classification to the above the number expected to be correctly classified by chance (Cohen 1960). Area under the curve values (AUC) were computed from receiver operating characteristic curves (ROC). Predicted = Predictor Present Actually Present Absent Actually Absent Present Actually Absent Absent Actually Present Present Correct Absent Correct AUC Total % Correct Cohen % Kappa Calcium-rich Invertebrate Biomass 15 9 10 4 0.789 0.474 0.65 63.2 26.3 Myriapod Biomass 14 9 10 5 0.737 0.474 0.69 60.5 21.1