Marine birds of Golfo Dulce: What do we know about them?

Bird watching is perhaps one of the most popular activities undertaken by visitors to Playa Cativo Lodge. In the area, which includes the surroundings of the Osa Peninsula, the Piedras Blancas National Park, and Golfito, you can observe more or less 400 species of birds of the more than 930 recorded to date for Costa Rica. If we think about birdwatching in Costa Rica our mind immediately takes us to a terrestrial trail, with the binoculars focusing on toucans, tanagers and hummingbirds. But how about   marine birds? Which species in particular can we refer to?

A recent study provides a general overview of the marine birds status of the Golfo Dulce. The results of “An updated checklist of the marine birds (Aves) of Golfo Dulce, southern Costa Rica” indicate that the marine avifauna of the Golfo Dulce is composed of 73 species in 16 families. Twenty species are resident and 50 are Neartic migrants. Two species have resident and migratory populations, and one is a breeding migrant. In this list obtained between 2007 and 2023, four species are classified as globally Near Threatened by the International Union for Conservation of Nature (IUCN).

  • Sea birds are colonial species that feed in salt waters and often migrate long distances from their breeding grounds to their wintering grounds. In some cases, these birds can connect geographically different marine environments. This group includes tropic birds (family Phaetontidae), petrels and shearwaters (family Procellariidae), frigates (family Fregatidae), boobies (family Sulidae), cormorants (family Phalacrocoracidae), pelicans (Pelecanidae), oystercatchers (family Haematopodidae), skuas (family Stercorariidae), and gulls and terns (family Laridae).
  • Shorebirds spend their lives on sandy beaches, salt marshes, and shores of rivers and lakes, and generally only interact with the edge of the marine environment. This group includes the avocets (family Recurvirostridae), the plovers and lapwings (family Charadriidae), and the curlews, sandpipers, turnstones and phalaropes (family Scolopacidae).
  • Aquatic birds live and feed mainly in fresh water and generally interact with the marine environment only in the coastal zone. This group includes storks (family Ciconiidae), anhingas (Anhingidae), herons and egrets (family Ardeidae), and ibises and spoonbills (family Threskiornitidae). 

According to the study, the family of curlews, turnstones, sandpipers, and phalaropes (Scolopacidae) was the most abundant, which is expected due to the suitability of the coastal habitats in the Golfo Dulce as a feeding ground for this group of birds. These birds congregated in river mangroves, with highest concentrations at the mouths of the Esquinas, Coto Colorado and Tigre rivers, and at Playa Azul, a long sandy beach near Golfito Bay. Furthermore, the four species whose IUCN conservation status is classified as Near Threatened were observed in these congregation sites; the Reddish egret (Egretta rufescens), the Elegant tern (Thalasseus elegans), the Semipalmated sandpiper (Calidris pusilla) and the Snowy plover (Charadrius nivosus).

A list of species, something that all bird watchers do every time they go out to observe, seems very simple but hides a unique value when it provides information over time. Birds, as indicators of the quality of the environment, allow us to analyze changes in ecosystems, whether of natural or anthropogenic origin. The effects of climate change, which are expected to impact marine and coastal areas, make it essential to understand the distribution of birds in these environments in a time frame. Species lists can provide reliable information on changes in bird populations, phenology, and geographic and climatic patterns, which is information required to formulate management and conservation strategies.

There are several studies regarding terrestrial birds in the adjacent forests of Golfo Dulce, in addition to well-established monitoring programs. However, marine bird studies and research in Golfo Dulce are marginal, despite its biological importance for birds. The only information available until 2023 was a list of species compiled by the former Instituto Nacional de Biodiversidad through the Unidades Básicas de Información (UBI) in 1998; a list that was already 25 years old!

Thanks to modern tools of citizen science, such as the eBird digital platform, and data obtained from the Golfito Bird Counts (on two marine routes), it was possible to collect information, update, compare, and verify the species registered on the UBI list. In addition, data from incidental observations were used to document rare species3. These three methods made it possible to update the  marine birds checklist of the Golfo Dulce, a study that not only fills an information gap, but also demonstrates the scope of citizen science when it is correctly managed.Citizen science can conveniently contribute to the generation of knowledge, while addressing social dimensions. This highlights the relevance of projects such as the Golfito Bird Counts, from which most of the data for this study was obtained. The Golfito Bird Counts - an axis of Aves de Golfito - are an annual monitoring project, supported by community participation. It allows obtaining information to monitor environmental changes in the marine-coastal ecosystems of the Golfo Dulce, and analyze the long-term population dynamics of birds at the local level. This project also promotes that scientific knowledge should be accessible and beneficial to the community.

On your next visit to Playa Cativo Lodge, don´t forget to contribute to the monitoring of marine birds in the Golfo Dulce by recording your observations on the eBird platform.  On a kayaking tour to the Esquinas river mangroves, snorkelling, whale watching, or simply on your way to Playa Cativo you will notice marine birds around you. Share your bird observations through eBird with the user AvesDeGolfito, or by sending an email to Your contribution from the sea is very valuable!

To read the full study and download the list of species visit the following link:
Aves de Golfito thanks Playa Cativo Lodge for addressing its benefits to the local community by being one of the main sponsors of the Golfito Bird Counts. 


By: Alejandra Rojas-Barrantes Tropical biologist, Nature interpreter