Background

Each year, migratory waders link ecosystems across the world, impacting their structure and functioning with consequences in the diversity and stability of local communities. Surprisingly, the role of migrants in ecological networks is poorly understood. Migratory shorebirds are seasonal in their over-wintering and stopover areas, but often occur in exceptionally large numbers, making them highly relevant predators of benthic invertebrates in most intertidal systems. Migrants can exert top-down regulation on prey populations or promote enough selective predation pressure to change prey population dynamics. Through cascading effects these changes can impact multiple trophic levels as well as nutrient regimes, potentially affecting the whole ecosystem. The link between predators, biodiversity maintenance and ecosystem resilience has been recently highlighted, with increasing evidence on the role of predators in deterring prey dominance and competitive exclusion, thus promoting diversity through top-down processes. Predators are often the first to disappear, threatening ecosystem stability and resilience. Half of all migratory shorebird populations are declining worldwide, mainly in result of human activities, representing a matter of international conservation concern. In spite of this, their role of shorebirds along their migratory routes has mostly been underappreciated, hindering to quantify the impacts of their potential loss.