Waterbird use of water hyacinth in Lake Chapala, Mexico: Implications for invasive weed management

Lake Chapala, located in the central highlands of Mexico, provides water for more than 10 million people, agriculture, and a regionally important fishery. Among Lake Chapala’s greatest biological assets is its diversity of waterbirds, including many migratory species. The lake also contains water hyacinth, a highly mobile, floating invasive weed that thrives in nutrient-rich waters. At high densities, the weed is problematic to boaters, fishermen, and irrigation systems. Herbicides are currently being applied to the lake to reduce water hyacinth density, but little consideration has been given to how this management approach will affect the resident and migratory bird community. We investigated how Lake Chapala waterbirds use water hyacinth by conducting seasonal surveys at 20 randomly selected sites that vary with respect to water hyacinth density. At each site, we identified bird species and counted individuals present in each of five habitat types: water hyacinth, submerged trees, emergent vegetation, open shoreline, and open water. We found a significantly higher total abundance of waterbirds at sites dominated by water hyacinth (p < 0.0001), although site-level abundance varied by species. Waterbirds were found most frequently in shoreline water hyacinth, and abundance observed in water hyacinth habitats was significantly higher than within other emergent vegetation (p <0.0001), open shoreline (p <0.0001), and open water habitat (p < 0.0001). Our results suggest that a population reduction of water hyacinth may cause changes in lake-wide habitat structure and prey availability that could negatively impact the Lake Chapala bird community.