Colony persistence in waterbirds is constrained by pond quality and land use

Abstract

Summary The conservation of wetlands, many threatened by human activities, is paramount to sustaining global biodiversity. Yet the protection of targeted wetlands may not be sufficient to protect the species they host because some species may also be impacted by alterations to the surrounding landscape. Some black‐headed gull (Chroicocephalus ridibundus: Laridae) populations have experienced a sharp decline in population size and number of colonies. Here, we investigated the relative contributions of wetland and its surrounding landscape to two major determinants of population dynamics, i.e. habitat selection and reproductive success, using 37 years of monitoring data. Our analyses revealed that large areas of cultivated land surrounding ponds and high vegetation cover of helophytes promote longer occupation of a pond by gull colonies, probably because they allow better reproductive success. We also found that both agricultural practices in surrounding landscapes and pond vegetation cover have sharply changed over the past 30 years in the study area, with an intensification of the former and a general decrease of the latter. These alterations are likely to have led to the observed decrease in the number of breeding gulls. The decrease in helophyte cover may have reduced their ability to construct nests in vegetation that protects them against flooding, and agricultural intensification may have decreased food availability during the crucial period of reproduction. Our study provides additional evidence, from long‐term changes in habitats and reproductive success, that in order to be effective, waterbird conservation plans should consider the terrestrial landscape surrounding wetlands, in addition to the quality of the wetland.