Relationship between species abundance and food distribution.

Models were fitted using a COZIGAM with a Poisson link function and measuring the joint effects of distance to the nearest feeding source (distance) and human presence (slope in Europe and cattle in Africa) on the spatial abundance of Egyptian Vultures and blackkites in their summering (Europe) and wintering (Africa) groundsResults for each spatial unit are shown for all seasons pooled in a single model. The table shows the proportion of 0 counts (% 0) in the dataset for each spatial unit. A linear model with a logit link function relates the probability of Zero-inflation (pi) to the covariates through the estimated spatial abundance in the GAM; in this model α is a constant and δ is a parameter measuring the homogeneity of Zero-inflation. The column for the “Effect of covariates” contains the estimated degrees of freedom (e.d.f) for each non-parametric term in the GAM, unless a parametric (functionally linear) term is selected; in these cases, denoted with the symbol ‘*’, the parametric estimate is shown instead. Statistically significant terms are shown in bold. Human density was measured as the density of cattle in Africa and the slope of the terrain in Europe. †The BIC denotes the Bayesian Information Criterion; the model minimizing this quantity is selected as the best descriptor of the dataset within the pool of fitted models, and is shown in bold type.