Latitudinal Gradients and Local Variations in Species Richness and Structure of Bird Communities on Raised Peat-Bogs in Sweden

Abstract

Bird species richness increases strongly with bog area. Slopes of log-log area-species regressions (z-values) on raised bogs are high (0.35-0.62), even when only large (> 100 ha) bogs are considered. The density of most waders is higher on larger (> 50 ha) than on smaller bogs. Wader density increases northwards and also as bogs become rounder and wetter. It is suggested that variations in wetness, predation pressure and food density are the causes of these patterns of wader density. The density of passerines decreases northwards but for other groups the reverse trend is present. The increasing wetness northwards on raised bogs and the higher density of rodents are possible causes of these trends. From a conservation point of view, one large bog is on average more valuable than several small bogs with the same combined area.