24 Hours || The oystercatcher faces a new breeding season in the Maipo River Wetland

The Río Maipo Wetland Nature Sanctuary, one of the most valuable ecosystems on the central coast, is once again the site of a new breeding season for the American oystercatcher (Haematopus palliatus), a keystone species in Chilean coastal biodiversity. However, its survival continues to be threatened by predation, storm surges, and the presence of uncontrolled dogs.

The wetland, managed by the Cosmos Foundation, is home to more than 190 species of birds, which is equivalent to 40% of the national avifauna, and is an essential refuge for migratory birds that arrive from the northern hemisphere to the southern Pacific coast.

In this environment, where fresh, brackish and marine waters converge, each nesting season of the common oystercatcher becomes an indicator of the ecological balance of the place, recognized as a site of regional importance by the Western Hemisphere Shorebird Reserve Network (WHSRN).

Between 2020 and 2024, monitoring by the Chilean Network of Bird and Wildlife Observers (ROC) and the Cosmos Foundation recorded between 21 and 46 nests per season, with an average of 45 eggs annually. However, only three nests hatched during the entire period, and only one chick fledged.

During the last season (October 2024 – April 2025), 30 nests and 47 eggs were recorded, but none hatched—a situation the teams hope to reverse this year. The common oystercatcher is classified as “Near Threatened” under the Species Classification Regulation (SCR).

Predators, storm surges, and uncontrolled dogs

The main threats identified include natural predation, storm surges, and the presence of unleashed dogs in nesting areas. Human disturbances, such as traffic on dunes or recreational activities, also have an impact, causing nests to be abandoned and breeding pairs to be displaced.
“The common oystercatcher is one of the most characteristic species of the Maipo River Wetland, and its reproduction reflects the challenges of this ecosystem. That’s why, along with scientific research, we are promoting concrete actions such as the Responsible Pet Ownership Program, which seeks to reduce the impact of uncontrolled dogs on biodiversity,” explained Diego Urrejola, executive director of Fundación Cosmos.

Conservation and science in the field

Since 2020, the Cosmos Foundation and the ROC have been developing a comprehensive conservation program for the common oystercatcher, which includes ringing individuals, periodic resightings, systematic monitoring of nests, annual survival assessment, and the installation of exclusion fences to protect critical nesting areas.
Thanks to this work, today there is the first population database on the common oystercatcher at the mouth of the Maipo River, which has allowed for a better understanding of its behavior and threats.

This collaborative effort reaffirms the Maipo River Wetland as a strategic site for the conservation of coastal and migratory birds in Chile. In a context marked by urban pressure and climate change, the continuation of these programs represents a concrete opportunity to protect a unique ecosystem of the central coast and ensure that the song of the Chilean oystercatcher remains part of the Chilean coastal landscape.