A recently published international study reports there are fewer and fewer large bodied bird species in Africa, Latin America and Asia. Led by a large team of researchers based at Institute of Environmental Science and Technology at the Universitat Autònoma de Barcelona (ICTA-UAB), the study finds that birds living in these regions are considerably smaller than those that predominated in 1940. The study documents the collective ecological memories of 10 Indigenous Peoples and local communities and reports a reduction of up to 72% in the mean body mass of the bird species present in these areas between 1940 and 2020.
“The project began in 2013, during my PhD fieldwork in the Bolivian Amazon,” ethnobiologist Álvaro Fernández-Llamazares told me in email. Dr Fernández-Llamazares works as a senior researcher at the ICTA-UAB. “Knowledge holders of the Tsimané people repeatedly told me that the large birds they had grown up with were rapidly disappearing.”
The Tsimané are indigenous people living in lowland Bolivia. They are primarily a subsistence agriculture culture, although hunting and fishing also contribute to many of the settlements’ food supplies.
“The Tsimané interact with birds on a daily basis through hunting, farming, rituals, and storytelling, which gives them long-term ecological memories that extend far beyond the timeframe of scientific monitoring,” Dr Fernández-Llamazares explained to me in email.
“As I later worked with Indigenous communities in other parts of the world, I realized that remarkably similar observations were being made elsewhere. That convergence made me realize that these place-based memories could reveal large-scale patterns of biodiversity change. This is what motivated me to carry out a global analysis to understand what Indigenous and local knowledge systems can tell us about long-term changes in bird populations.”
F I G U R E 1 : Locations of the ten study sites.doi:10.1017/s0030605325102615
The research is based on a global survey of 1,434 adult participants from 10 place-based communities across three continents (Figure 1). In total, Dr Fernández-Llamazares and collaborators surveyed 1,434 adults in ten communities in Bolivia, Chile, Mexico, Brazil, China, Ghana, Kenya, Madagascar, Mongolia, and Senegal. They compiled 6,914 unique bird reports (Figure 2) corresponding to 283 bird species, and compared the bird species most commonly reported during participants’ childhoods with those currently reported in their territories.
Distribution of bird reports over time in the 10 study sites (Fig. 1) and across all sites combined.
The reported differences in bird species were statistically significant in territories such as Tsimane (Bolivia), Timucuy (Mexico), Vavatenina (Madagascar) and Ordos Desert (China). At the same time, no significant differences were reported for Lonquimay (Chile) and Bulgan soum (Mongolia).
The Indigenous Peoples’ cultural memory strongly contrasts with most people’s memories of environmental conditions, which are continually deteriorating over time, a phenomenon known as the Shifting Baseline Syndrome (ref). Basically, in the absence of past information or experience with historical conditions, members of each new generation accept the situation in which they were raised as being “normal”. This psychological and sociological phenomenon is increasingly recognized as one of the fundamental obstacles to addressing a wide range of today’s global environmental issues.
Dr Fernández-Llamazares and collaborators’ analysis reveals the deeply worrying pattern where large bodied bird species are rapidly disappearing from local environments, only to be replaced by smaller bodied species. For example, this study found that the average mass of reported bird species exceeded 1,500 grams (3.3 pounds) in the 1940s, whereas the average mass in 2020 is reported to be closer to 535 grams (1.17 pounds). This coincides with a significant decline in body mass of 72% over eight decades.
The secretary bird (Sagittarius serpentarius) is a large endangered bird of prey that is endemic to open grasslands and savannah of the sub-Saharan region of Africa. Its body mass ranges from 2.3kg to 5kg (5–11 pounds)
What happened to these large birds? They were likely driven locally extinct because large bird species are more vulnerable than small ones to hunting, habitat destruction and fragmentation, and to infrastructure development, according to Dr Fernández-Llamazares. Further, the loss of these birds threatens biodiversity and environmental health and is accompanied by the loss of key functional roles held by these birds in their ecosystems, particularly seed dispersal, pest control, and forest regeneration.
Dr Fernández-Llamazares and collaborators’ study serves to highlight critically important alterations to the intimate, lived experiences with nature of generations of people within their territories. It also points to the collective impoverishment of Indigenous Peoples’ cultural identity, memory and traditional practices around the world.
“Bird declines are not abstract statistics: they are visible, remembered, and felt by people who live closest to nature,” Dr Fernández-Llamazares stated in email. “When ten Indigenous Peoples and local communities across three continents independently report that birds are getting smaller, it tells us the avian extinction crisis is deeper and more pervasive than we tend to acknowledge with scientific data.”
Source:
Álvaro Fernández-Llamazares et. al. (2026). Indigenous Peoples and local communities report a consistent decline in the body mass of birds across three continents, Oryx | doi:10.1017/s0030605325102615
