ECR Feature: Thiago Laranjeiras on avian diversity in Amazonian floodplains

Thiago Laranjeiras is an an environmental analyst at Instituto Chico Mendes de Conservação da Biodiversidade. He is a biogeographer with a keen interest in the ecology and biodiversity of birds. Thiago shares his recent work on transitions in avifauna communities across floodplain habitats in the Amazon.

Name. Thiago Orsi Laranjeiras

Personal links. Web page | ResearchGate | Flickr

Institute. Instituto Chico Mendes de Conservação da Biodiversidade (Chico Mendes Institute for Biodiversity Conservation)

Current position. Environmental analyst.

Major research themes. Biogeography, ecology, natural history, ornithology, and conservation.

Current study system. I studied Amazonian birds during my PhD, especially those that inhabit floodplain forests. Amazonia is home to more than 10% of all known bird species, yet most of them are poorly studied and are data deficient. Many of the birds that inhabit the Amazonian floodplains are habitat specialists and have restricted distributions. They are conspicuous, with loud beautiful songs that can travel far distances over river water. Listening to a dawn-chorus while drifting down the river in a boat is an incredibly peaceful activity.

Klagesi’s antwren, Myrmotherula klagesi, one of the floodplain forest bird specialists that best represent the effects of the confluence of the Negro and Branco rivers for the floodplain avifauna

Recent paper in JBI. Laranjeiras TO, Naka LN, Leite GA, Cohn-Haft M. Effects of a major Amazonian river confluence on the distribution of floodplain forest avifauna. J Biogeogr. 2021;48:847–860.

Motivation behind this paper. One of Amazonia’s most striking features is the diversity of “colors” of its many rivers. Different drainages associated with distinct geological features (the Andes, the sandy-soil lowlands or the Brazilian and Guianan shields) create ‘white’, ‘black’, and ‘clearwater’ rivers. These different river types are also associated with varying biodiversity. Previously, comparing distinct rivers in the Rio Negro basin (in northwestern Brazilian Amazonia), the world’s largest blackwater river, it became clear that these nutrient-poor waters create floodplain forests that contain distinct avifauna from those found in sediment-rich whitewater rivers. However, not everything was “coffee au lait” or “weak black tea”. We found “intermediate” avifauna in some of the rivers. Also, rivers of distinct water types can meet and such river confluences, as critical hydrogeological phenomena, may have important implications for floodplain systems. Those who are familiar with the “meeting of the waters” of the Rio Solimões and the Rio Negro itself, in front of Manaus (the largest Amazonian city), can easily notice the magnitude of such confluences. The relevance of mixing distinct water types on floodplain terrestrial fauna has so far been largely overlooked. So, we went to the Rio Negro at the confluence with its largest tributary, the sediment-rich whitewater river, the Rio Branco, to characterise diversity variation between mixed and unmixed water types.

The meeting of two Amazonian rivers, showing the contrasts in the water and in the floodplain forests (the blackwater Rio Canumã and the whitewater Paranã do Urariá, in the Brazilian state of Amazonas)

Key methodologies. To investigate how the entrance of the Rio Branco affects the avifauna along the Rio Negro, we implemented a rapid and standardized avian sampling of floodplains of both riverbanks and nearby islands, above and below the confluence of the two rivers. Focusing on the commonest bird species that are easily identified by song, this rapid and standardized sampling allowed us to cover a huge area in a relatively small time period (stretching more than 400km of rivers). It took us a few field expeditions to sample 52 sites. More complete and traditional avian inventories would take decades. In a similar way, we retrieved estimates of sediment concentration in river water (a main parameter in Amazonian water type classification) using satellite imagery. Covering a 15-year time-series, these estimates avoided the limitations of direct measures of sediment concentration in the field in a single period and allowed us to better understand the variation throughout the confluence of these two rivers.

Major results. We found a mixed and richer avifauna along the Rio Negro below its confluence with the Rio Branco. Bird species that are typical of whitewater floodplains occurred predominantly on the left riverbank or nearby islands of the lower Rio Negro, on the same side into which the Rio Branco sediment-rich waters seem to be channelled. Rather than just representing a potential blackwater barrier between whitewater systems, the lower Rio Negro comprises a unique biogeographical transitional zone. These results indicated the importance of the dynamics and distribution of nutrient-rich sediments and that confluences of large Amazonian rivers not only affect aquatic species, but also the distribution of floodplain terrestrial fauna. Several other confluences of contrasting large rivers occur throughout the Amazon and these phenomena emerge as a key factor explaining boundaries of species’ distributions and geographic patterns of Amazonian floodplain biodiversity.

Wire-tailed Manakin, Pipra filicauda, a typical floodplain forest bird species of the Rio Negro basin

Challenges you overcame. Despite our rapid approach, sampling all the 52 sites along the confluence still had its challenges. To optimize the time in the field, we had to navigate at night from one site to another, including along stretches away from the main channel of the river. Given water level of the river was descending, some sandbars were still submerged, but close to the water surface. Navigating in this situation requires a lot of experience from the boat driver and the use of the sonar to avoid hitting the sandbars.  However, one time we miscalculated, and our boat literally jumped out of the water! Fortunately, it was a small sandbar, so we narrowly missed a stranding that would have been disastrous for continuing our field work!

Thiago boating between sampling sites.

Next steps. To look at other dimensions of the diversity than taxonomic (phylogenetic and functional) is a natural next step for understanding heterogeneity of the Amazonian floodplains and the importance of major river confluences. Investigating other confluences will also shed light on the generality of the patterns we found. Overall, synthesis of avian geographical patterns in Amazonian floodplains would offer a new background for future studies on the evolution of these ecosystems, providing new guidelines for conservation of Amazonian avian diversity. I hope such work is conducted in the near future.

If you could study any organism on Earth, what would it be? Birds are organisms hard to let aside. Their diversity and geographic patterns are captivating. Rather than other organisms, I feel that I would study birds from other regions. Amazonia is deeply fixed in my dreams. There are other huge and interesting rivers confluences and even poorly explored rivers, filled with poorly known birds and communities. I have been talking to myself for years about a long-term expedition, navigating through several Amazonian rivers from the mouth to their headwaters. Also, on my radar are the remote, almost untouched Amazonian mountains, the tepuis. Recently, I also had the opportunity to explore some of them, but this is another subject. Altogether, I feel that Amazonia is where we arrived with one question to leave with ten or to never more leave.

Sun rise provides an incredible background for listening to the dawn-chorus of birds in the floodplain forest of Anavilhanas in the lower Rio Negro.

Anything else you’d like to add? I would like to say that this research, as well as my journey as a biologist, would not be possible without support from many important people and institutions. To study birds in the remote Amazonian floodplains is a privilege. I feel that I am worth of such privilege by making Amazon my home for more than 15 years. As an environmental analyst, I also have the opportunity to apply and put in practice the ecological and biogeographical concepts into biodiversity conservation, especially regarding the protected areas in the Brazilian state of Roraima. To put these concepts into conservation practice is a duty that I am happy to deal with. Finally, I think we still need to improve our ability to communicate our results from biodiversity research with the general public, using all available media. I hope here we make greater progress in this area.

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