Introduction. Waterbirds that inhabit seasonal environments often perform migratory movements in response to changes in the landscape, usually to optimize the use of food resources or to nest. Most of our knowledge on migratory movements in waterfowl comes from species that inhabit temperate regions. However, ample evidence show that this type of movement also occurs in tropical birds. Seasonal changes in the landscape created by the flood pulse of Amazonian rivers can result in migratory movements, particularly in beach-dwelling species that find their preferred habitats completely flooded for several months each year. Objective. In this study, we used GPS transmitters to assess the potential seasonal movements in populations of two bird species, the Orinoco Goose (Oressochen jubata) and the Skimmer (Rynchops niger) in northern Amazonia. Methods. The birds were captured in February 2020 and March 2022 in the lower Rio Branco, in the Brazilian state of Roraima. Skimmers were captured using mist nets and geese by snare traps. We placed transmitters on seven Orinoco geese (4 ARGOS and 3 IBIS) and nine transmitters on Skimmers (4 MTI, 4 Lotek and 1 Ikarus). Geographic locations were transmitted every two hours for geese and on variable schedules for skimmers depending on transmitter model. The data was automatically uploaded to Movebank.org and trajectories analyzed with QGIS. Results. The eight transmitters installed in 2020 resulted in between 418 and 710 days of monitoring on the geese and between 2 and 242 days of monitoring on the skimmers (two skimmer individuals provided few days of data in 2020). All monitored individuals left the lower Rio Branco when the beaches were completely flooded (when the fluviometric average was ~3 m). The geese moved ~400 km north to spend the flood season in the rice fields in the savannas of Roraima, along the Tacutú and upper Branco rivers. Data collected from six skimmers allowed us to recognize three different migratory routes: four individuals moved north to the coast of Suriname (2 in 2020 and 2 in 2022), one individual went east towards the coast of the Brazilian state of Pará (2020) and preliminary data from a tagged individual in 2022 indicate southeastward movements to the Rio Solimões, probably en route to the coast. Conclusions. This study revealed novel seasonal movements associated with the fluctuation of the water level of an Amazonian river, suggesting that these kinds of movements are potentially widespread in Amazonian beach-dwelling birds.
Amazon, River beaches, Birds, Migration.