Habitat-mediated influence of water-level fluctuations on waterbird occurrence in floodplain wetlands of the Parana River, Argentina

Abstract

Responses of waterbirds to habitat variation could account for their responses to fluctuations in river levels because hydrological fluctuations influence habitat availability across floodplains. Relationships between water level and waterbird occurrence were examined in floodplain wetlands of the Middle Paraná River to assess (a) whether occurrences of waterbird species were associated with water-level fluctuations of the river, (b) which habitats were associated with species that showed a relationship with water level, (c) the influence of water level on these habitats, and (d) whether influence of water level on these species was related to water-level influence on habitats. Through the use of regressions and structural equation models, we assessed whether direct relationships between each species and water level remained important after considering the influence of habitat variation. Of 21 species analysed, occurrences of 12 species showed an association with water-level fluctuations. Indirect effects of water level through habitats fully accounted for this association in 5 species. Variation in habitat conditions did not, however, fully account for responses of 6 species, suggesting that although habitat variation can be an important factor, other variables are necessary to explain responses of some species to water level. One species was not associated with any habitat and therefore was not included in this analysis. Our results agreed with the idea that an important fraction of waterbird responses to hydrological fluctuations is related to the effects of these fluctuations on the availability of habitats across the floodplain. Our results provide data that help delimit groups of waterbird species that respond in similar ways to hydrological fluctuations.