Spatio-temporal responses of a migratory shorebird community reflect complex trade-offs among overabundance of predators and disturbance

Animal selection of foraging grounds is a trade-off among available feeding resources, intra and interspecific competition, disturbance and predation risks. The present study was carried out at Kadalundi-Vallikkunnu Community Reserve on the West coast of Kerala (India) in the Central Asian Flyway. The Reserve hosts different coastal habitats, including mudflats, mangroves and sand beaches, and although 31 species of shorebirds are commonly present, it is heavily impacted by human activities. The findings highlight the necessity of robust management of anthropogenic waste and reveal the detrimental impacts of human activities on species communities of conservation concern. We investigated how the densities and intake rates of nine migratory shorebird species responded spatially and temporally (9 years) to a complex situation where different levels of disturbance, prey density, densities of predators and shorebirds were found among three habitats. Human activities, specifically waste disposal, acted as a continuous over time anthropogenic resource subsidy and significantly affected predator density, resulting in overabundant predator density and high attack rates. The densities of all shorebirds were positively regulated by shorebirds and prey densities and affected by habitat type and year. The density of predators and attack rates negatively affected the densities of shorebirds. Despite this, all species continued to concentrate to feed at the beach, the habitat with the second highest density of predators but also of prey. It is hypothesized that the high predator density and attack rates were above a natural upper threshold, making the three habitats equally dangerous. Most of the intake rates of the different shorebird species were positively regulated by the density of shorebirds and affected by habitat type, season, and year. Nearly half of the shorebirds' intake rates were negatively affected by the density of predators or predator's attack rates. Our results showed that non-lethal effects (reduction of energy intake) were at play in a situation where a continuous anthropogenic resource subsidy resulted in overabundant predator density and high attack rates. Practical implication: In the context of overabundant predation pressure and disturbance, shorebirds used public information and habitat structure/cues to congregate in the habitat that was signalled as the best feeding and safest habitat, the beach. In a system where a clear situation of anthropogenic resource subsidies to predators exists resulting in overabundant predator density and high attack rates and with signs of non-lethal effects (reduction of energy intake), it is urgent to upgrade significantly the waste management plan in order to decrease overabundant predators and improve habitat quality for migratory shorebirds. Under the situation where shorebirds use public information and habitat cues to concentrate in specific feeding grounds, they can be attracted to areas that can act as ecological traps. And migratory species that are under high energetic demands and depend on few high-quality habitats scattered along their migratory routes are particularly at risk.