EFFECTS OF THE ALQUEVA DAM RESERVOIR ON DISTRIBUTION OF STEPPE BIRDS

Abstract

The aim of this article is to describe the effects of the Alqueva dam reservoir on the Steppe bird’s pattern distribution, measuring the bird’s pattern before and after flooding using point-pattern analysis. To this end, we made use of sampling points from the dam biological monitoring program, which included data from winter and breeding seasons. To quantitatively assess spatial patterns, we tested the bird’s point-pattern, applying 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 bird’s suitable habitat. A gradient surface of probabilistic abundance with Kernel Density Estimator was developed and compared with the Kappa Index of Agreement.