Between 1999 and 2018, researchers carried out audiovisual bird surveys around Belém, on ten farms in the municipality of Igarapé-Açu, and along the Atlantic coast of the Salgado paraense. The observations were woven into three agroecological research projects, allowing nearly two decades of repeated visits under real farming conditions. Observers worked long daily windows, typically from 07:30 to 16:00, using standard 10 × 42 mm binoculars and point-stop counts during weekend excursions. When the dust settled, the compiled lists reconfirmed 300 bird species across 220 genera and 62 families, a remarkable total for a region often written off as biologically depleted.

The central question was deceptively simple: has the bird community of the Bragantina already crossed the threshold from rainforest to savanna? The landscape today looks strikingly open, a process the researchers describe as savannization, in which structural simplification mimics the physiognomy of a savanna even before any full climatic biome shift has occurred. Climate projections for the northeastern Amazon point toward hotter and drier conditions by the end of the century, which could accelerate this transformation. If land-use intensification and climate change had already pushed the region past a tipping point, the avifauna should now resemble that of the savannas of neighboring Maranhão rather than the ancient rainforest biome.

To answer the question rigorously, the team employed a battery of quantitative tools. Non-metric multidimensional scaling, or NMDS, was used to visualize similarities among species lists, based on Bray–Curtis dissimilarity for site-level comparisons and Jaccard presence–absence data for regional inventories. Beta diversity was partitioned into two additive components using the betapart package in R: true species turnover, which reflects the replacement of species between sites, and nestedness, which reflects species loss where one community is a subset of another. Diversity itself was quantified with Hill numbers at three orders of q, capturing species richness, Shannon diversity and Simpson diversity, and integrated rarefaction and extrapolation curves generated with the iNEXT package ensured that comparisons were robust to differences in sampling effort, with 95 percent confidence intervals computed from 200 bootstrap replications.

The results were unambiguous. When the assembled avian data from Igarapé-Açu and Belém were plotted against historical reference lists, they clustered far closer to the rainforest avifauna of the old Bragantina, documented by Forrester in 1993, than to the savanna bird communities of Maranhão or São Luís. The hypothesis of a completed biome shift was therefore rejected. Even more telling was the beta diversity partitioning. Between the historical Belém reference and the current rural landscape, total Sørensen dissimilarity reached 0.320, but this was split almost evenly between turnover at 0.167 and nestedness at 0.154. A genuine biome shift would have been dominated by turnover; the near-equal nestedness component reveals that the rural community remains, to a large extent, an ecologically impoverished subset of the original rainforest avifauna, a degraded rainforest matrix that still preserves its Amazonian history.

Within the rural matrix itself, the picture was even clearer. Comparing Igarapé-Açu with the historical Bragantina list yielded a much lower total dissimilarity of 0.166, almost entirely attributable to turnover at 0.160, with negligible nestedness at 0.006. The Hill number profiles reinforced the message of resilience. Igarapé-Açu recorded the highest observed species richness at 196 species, edging out Belém at 186, and its effective numbers of common species remained high as well. The high values at the Shannon and Simpson orders indicate an unusually even community, meaning the rural mosaic is not dominated by a handful of aggressive generalists but supports a broad assembly of birds. Notably, the confidence intervals for Tomé-Açu, a region with a different land-use history, did not overlap with those of Igarapé-Açu or Belém, confirming significantly lower diversity there and demonstrating how divergent ecological outcomes can emerge within the same Front Yard.

That is not to say the community has escaped change unscathed. Robust, widespread neotropical generalists such as the smooth-billed ani, Crotophaga ani, and the common ground dove, Columbina passerina, have become dominant, while the guira cuckoo, Guira guira, and the white woodpecker, Melanerpes candidus, have established themselves as indicators of the ongoing savannization. Up to 13 nacunda nighthawks, Podager nacunda, were documented at a single farm. Meanwhile, the large understory game birds of pristine rainforests, such as tinamous and the rufous-vented ground cuckoo, are virtually absent, a signature of local extirpation driven by two centuries of colonization and habitat fragmentation. Yet the presence of resilient forest raptors such as the black hawk-eagle, Spizaetus tyrannus, which were not recorded in the historical reference list, hints at a degree of habitat recovery within the rural matrix.

Equally intriguing is what has not arrived. Despite extensive open areas structurally analogous to their native habitats further east, typical semi-humid tropic species have largely failed to colonize the Bragantina. Doves common in Maranhão, Piauí, Ceará and Tocantins, such as Columbina minuta, C. squammata, Uropelia campestris and C. picui, have not expanded into the region, nor have several seedeater species or the red-crested cardinal. This limited invasion, possibly rooted in intrinsic reproductive constraints that limit the offspring surplus needed for territorial expansion, is another factor preserving the region’s Amazonian character. The regional environmental filter, it seems, still favors forest-affiliated taxa even in a structurally simplified landscape.

The study also delivered records of conservation significance. The red-shouldered macaw, Primolius maracana, classified globally as Vulnerable, was recorded across ten distinct farms and sites spanning the area from Salinópolis to Castanhal, with large flocks of up to 34 individuals previously documented, encouraging evidence for the stability of this isolated northeastern Pará population. A single individual of the Vulnerable golden parakeet, Guarouba guarouba, was discovered at the Embrapa facility in August 2007, though it was likely an escaped bird attempting to join a flock of jandaya parakeets. Coastal surveys produced a magnificent frigatebird in September 2007 and a parasitic jaeger in March 2007, both of which predate the earliest previously documented records for Pará, and a Picumnus woodpecker photographed in the mangroves of Algodoal added to a lingering taxonomic puzzle on the northeastern coast.

The authors argue that these findings should reshape conservation strategy in the Bragantina. Rather than concentrating solely on the last remaining pristine forest specialists, it may be more promising to protect robust, common-to-rare Amazonian bird species that can follow dynamic land-use changes. Endemic canopy species such as the white-tipped cotinga, Xipholena lamellipennis, might survive in the region if sufficiently large forest patches and key mast fruiting trees are protected and planted at regular intervals across the whole landscape, as exemplified by the isolated military rainforest patch near Peixe-Boi. Because land use in the Bragantina shifts with fluctuating commodity prices, the researchers call for landscape-level connectivity, a heterogeneous matrix of capoeira successional stages, riparian corridors and agroforestry homegardens, to prevent further biotic homogenization. With smallholders lacking access to Portuguese-language field guides and local bird monitoring groups absent, engaging these critical stakeholders could ensure that the rural Front Yard remains a resilient reservoir of neotropical biodiversity, full of positive surprises.

Subject of Research: Bird community composition and biodiversity patterns in the deforested rural Bragantina region of the eastern Amazon

Article Title: Avian composition in the rural ‘Amazon Front Yard’ still retains its humid tropical identity

Article References: Avian composition in the rural ‘Amazon Front Yard’ still retains its humid tropical identity. (n.d.). https://doi.org/10.3897/neotropical.21.e180457

Image Credits: AI Generated

DOI: 10.3897/neotropical.21.e180457

Keywords: Amazon, birds, biodiversity, deforestation, savannization, Belém, Brazil, conservation, Neotropical Biology and Conservation, Avian, composition, rural