Visit the Asunción Bay Management Plan webpage
Asunción Bay is located on the border between the eastern region and the Chaco, along the banks of the Paraguay River. It has a surface area of approximately 375 hectares and is only two kilometers from downtown Asunción. It is one of the most important stopover places for Nearctic and austral migratory birds.
Migratory birds come from different places on the globe, travelling along different routes. They are subdivided into various groups based upon the seasonal movements. The Nearctics come from North America during the austral summer; the australs come from different points in South America during various seasons. All of these may only “pass through”, but in some cases some may stay for an entire season.
Asunción Bay has a wide variety of habitats, although their occurrence may change due to large seasonal fluctuations in the water level of the Paraguay River – the depth and the floodplains of the bay vary considerably. During the austral winter, with high water levels, the bay is largely underwater, but at the end of the season, as the water level falls, sand and clay beaches (marshes) appear. If the water continues receding, the “marshes” dry up and become grasslands, although some wetlands do remain. The majority of the records of aquatic birds correspond to these fluctuations, and their number rises notably with the fall of the water level. Many species that do not depend directly upon an aquatic habitat occur more frequently during the ebb tide.
A total of 258 bird species have been recorded, including 7 species under threat of extinction on a worldwide level and 28 species that nest in North America and migrate to the south of South America. More than 3% of the global population of one of these species, Buff-breasted Sandpiper (Tryngites subruficollis), passes through the bay during its southern migration, making Asunción Bay an Important Bird Area (IBA).
In Asunción Bay, one can find two types of migratory birds: Nearctic migrants and austral migrants. The Nearctics are species that reproduce in North America and pass the boreal winter in South America. Forty-two species of Nearctic migrants have been documented in Paraguay, with twenty-eight of these being recorded in the bay. The majority of these 28 species are Nearctic shorebirds that use the Paraguay River as a migration corridor on their path south, stopping in the bay to rest and feed.
In general, the austral migratory system is oriented south-to-north. It basically consists of birds from the south of South America that move further north, away from the cold climates of the austral winter. Forty-seven austral migrants have been identified: sixteen are true “Austral Migrants”, nineteen are “Northern Reproducing Austral Migrants” and twelve are “Southern Reproducing Austral Migrants”. The majority of the austral migrants are from the family TYRANNIDAE, with a total of 21 species. Regular monitoring in Asunción Bay was initiated by Floyd Hayes and Jennifer Fox, studying the migratory Nearctic shorebirds and the resident aquatic birds.
In September, 2000, Guyra Paraguay continued the monitoring of the bay (principally the “San Miguel Bank”) to investigate the importance of the site for Nearctic shorebirds, but also evaluating the importance of the area for other bird species. To date, more than 150 censuses have been conducted by Guyra Paraguay, resulting in greater knowledge of the birds of Asunción Bay.