Even in forests considered preserved, the disappearance of various bird species is being observed. Although initial suspicions pointed to traditional causes such as chainsaw use, tractors, pesticides, illegal mining, or criminal fires, the vanishing of these birds was noted in areas that were never deforested or significantly altered, and were frequented only for scientific research purposes.
The uirapuru (Cyphorhinus arada) is one of the species slowly declining, along with the short-billed leaf-warbler (Sclerurus rufigularis), the spotted choquinha (Myrmotherula guttata), the vite-vite-uirapuru (Hylophilus ochraceiceps), and others. The research that documented this decline was published in 2020 and is part of the Biological Dynamics of Forest Fragments Project (PDBFF), which began in 1979.
This project focused on 21 sites located 80 km north of Manaus. The objective was to replicate the previous work of Rob Bierregaard, an American zoologist, who studied birds in 34 locations between 1980 and 1984. The PDBFF data, collected between 2008 and 2016, allowed for a comparison between the two periods.
To capture the birds, mist nets were used, large structures measuring 12 meters long by 2.5 meters high, designed to trap animals without causing injury. Of the 79 types of birds captured and analyzed, 52 showed population decline, 24 showed an increase, and three remained stable. Notably, the uirapuru was no longer found in almost half of the investigated areas.
A comparative study conducted at the Tiputini Biodiversity Station (TBS), within the Yasuni Biosphere Reserve in eastern Ecuador, using the same mist net technique, registered a 40% drop in capture and observation rates between 2001 and 2014. In Panama, monitoring over 44 years in a 220 km² area in Soberanía National Park indicated that about 70% of the analyzed species suffered population decline.
The 2020 investigation, integrated into the PDBFF, led to an analysis of a new database containing 4,264 individual bird captures between 1985 and 2012 in the same region. The results, released in 2025, pointed to global warming as the main responsible factor. It was observed that dry periods became about 1°C warmer and 10 mm drier during the studied period.
The model from the new research suggests that a 1°C increase in the average temperature of the dry season can reduce the annual average survival of the studied community by 63%. Of the 29 species evaluated, 24 showed signs of population decline linked to climatic conditions. A central theory is that elevated temperatures reduce insect populations, which are the food source for insectivorous birds, which are ectothermic and sensitive to climate change.
With less food available, native birds may face physiological stress, resulting in lower reproductive rates, survival difficulties, or migration to areas with better food supply. This redistribution can destabilize established ecosystems. This pattern aligns with the original study, which showed that most declining birds feed on the ground looking for insects, while increasing species are those that benefit from warmer and sunnier climates, such as frugivores.
However, researchers warn that this is only a hypothesis, as no one has directly measured the decrease in insect populations in the study area. Ecologist Vitek Jirinec, one of the authors, classified the hypothesis as 'totally plausible,' given that most studied species are insectivorous and share the warming and moisture reduction with invertebrates.
The 2025 study offers direct proof of the link between hotter and drier climatic conditions and lower bird survival. Intact forests are not immune to the impacts of climate change, whose alterations in climate intensely influence the local microclimate. The loss of insects due to heat and the disappearance of birds due to lack of food are examples of this degradation.
Another relevant point is the scarcity of long-term studies in untouched areas. Data from the Global Nature Watch platform show that the extent of intact forest landscapes worldwide decreased by 15% (1.95 million square kilometers) between 2000 and 2025. The concept of pristine nature is debated, given that humans have always influenced nature, even in ancient indigenous settlements.
Tropical forests are distinguished by climatic constancy, creating a constant warm and humid microclimate, which favors ecological specialization. According to researcher Mario Cohn-Haft, disturbing this climatic constancy leads to the loss of highly specialized species in favor of more generalist ones. He fears that we are entering a phase of great threat and possible species extinction.
The consequences of this scenario are severe, as insectivorous birds control pests, preventing damage to vegetation through a phenomenon called trophic cascade. A 2025 review article confirmed that the combined decrease of insects and their predators can reduce native plant diversity. Thus, the future silence may not be one of contemplation, but rather of the absence of life caused by human-introduced changes.