Effects of the Surrounding Landscape on Waterbird Populations in Estuarine Ecosystems of Central Chile

Waterbirds have high potential as bioindicators of the status and functioning of estuarine ecosystems, because they respond to multiple stress factors in a wide range of spatial scales. The objective of this study was to analyze the dependence of the population size of waterbird species with different degrees of association with waterbodies (High: HAW, Low: LAW) on attributes of the surrounding landscape. This was accomplished by long-term monitoring (2006–2015) of the populations of waterbirds in three estuaries of central Chile; the Itata, Mataquito, and Reloca Rivers. We acquired data on the composition and structure of the landscape for each site from satellite sensors (Landsat TM5, ETM + 7 and OLI 8), specifically the normalized difference moisture index (NDMI). We also obtained the covers of grassland and crops, bare soil and shrubland annually (summer) using a supervised classification. Using point-count data (2013–2015) from the landscape surrounding the Itata estuary, we compared the proportion of the population of different species present within and outside the wetland. The negative temporal correlation (p < 0.05) between the number of Yellow-billed pintails (Anas georgica) inside and outside the estuary strongly suggests the movement of individuals between these two habitats. We found that the abundance of many species in in the estuaries was affected by the variation of some landscape attributes. However, that proportion of LAW and HAW species showing such relationships did not differ significantly. The most important attributes of the landscape for waterbird populations were moisture (flooded sites) and vegetation photosynthetic vigor, shrubland cover. The growing use of waterbird population data as an environmental monitoring tool requires a deep understanding of the factors that drive the changes in both population numbers but also in the data describing the latter. This study highlights the importance of incorporating into waterbird population assessments information from both inside the waterbodies and from their surrounding landscapes.