Pereira, M. & Figueiredo, D.

The effects of the Alqueva Dam reservoir on the distribution of steppe birds (before and after flooding) was quantified using point-pattern analysis. Sampling points from the dam biological monitoring program, which included data from winter and breeding seasons, were used. To quantitatively assess spatial patterns, the point-pattern was tested using a sequence of statistical methods. Autocorrelation was measured using Ripley's L-function and O-ring, and was validated by a complete spatial randomness null model in the birds' suitable habitat. A gradient surface of probabilistic abundance was developed with a Kernel Density Estimator and compared with the Kappa Index of Agreement. The results indicate a decline in the absolute abundance of steppe birds in both seasons, but it is more evident in the breeding season. The results also show an increase in the mean distance between the point surveys, some evidence of a global trend toward the northeast, a decrease of patch values, and a disaggregation of continuous patches.