GAM models for the probability of detection compared by AIC.

POD = probability of detection, d = distance, m = mass, surf = surface dry/wet, alt = altitude, spec = species. df gives the (estimated) degrees of freedom of the model. “:” indicates an interaction of all the variables and factors appearing in the term. The degrees of freedom for the mass smooth term was restricted to 5. Stars indicate the significance of a model comparison according to a Chi-squared test between each model and the best (first) model (under assumption of df), ***p<0.001, **p<0.01, *p<0.05.