The impact of human disturbance on nest predation patterns in freshwater marshes.

Abstract

Although predation is the major factor responsible for nest losses in birds, predation patterns in marshes and adjacent uplands are poorly known. This study examined the factors affecting nest predation on marsh-nesting birds found in areas affected by different intensities of human disturbance (urban, agricultural, natural). Artificial nests simulating waterfowl and passerine nests were used for that purpose. The nests, located along transects running from the center of the marshes to the adjacent upland habitats, were set up in the months of May, June and July 1989 and 1990. Eggshell remains were used to identify the predators. Predation was higher on passerine than on waterfowl nests and on nests located in upland habitats. Deep water prevented mammalian predators from foraging deep in the marsh. Predation rates in urban and natural areas were high while nests located in agricultural areas suffered lower predation. Nest camouflage was generally unimportant in reducing chances of predation. Mammals were responsible for most of the predation events. Differences in density and/or diversity of predators in urban, agricultural and natural areas were the main causes of different predation patterns observed in the three areas.