- Areas dominated by humans are home to fewer species, with similar ecosystem function and proximity in the evolutionary family tree, a recent study in Nepal’s southern plains suggests.
- Human activities act like a filter, letting only certain birds survive. Even natural areas show signs of such filtering when logging and hunting remove sensitive species, leaving behind only closely related groups of birds that are resilient and adaptable.
- A mosaic landscape provides more “homes” and more ecological roles for birds, helping them survive even amid human disturbances.
KATHMANDU — Birds prefer to live in a mix of forests, fields and wetlands, but human activities such as logging, hunting and sand and gravel mining are taking a toll on such mosaics in Nepal’s southern plains, a recent study shows.
The research, published in the Journal of Environmental Management, suggests such a mosaic of connected habitats coupled with a reduction of disturbances from human activities such as extraction may help boost not only the numbers of birds, but species as well.
“We found that while birds seek heterogeneity in their habitats, human activities are increasingly homogenizing the landscapes at the cost of bird habitats,” said Hem Bahadur Katuwal, assistant professor at Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences.
As part of the study, researchers studied the diversity, ecological traits and functions (habitat, diet, mobility and body size) and ancestry of 238 randomly selected bird species in an anthropogenic (farmland and settlement) and a natural (forest and riverine) habitat within the Parsa-Koshi Complex (PKC) in southern Nepal for more than a year.
“We chose the study area because it is not only rich in natural habitat, but it also has the highest population density in Nepal,” Katuwal said.
Katuwal and his team then used computer models to compare this data with the level of human activity and landscape patterns in the same area, aiming to see if human activities acted like a “filter” that only allowed certain types of birds to survive.
The study found that human activities potentially reduce the number and variety of birds, making communities simpler. On the other hand, landscapes that have lots of different habitats such as forests, rivers and open areas mixed together support more bird species. This could be attributed to the availability of varied “homes” and roles for birds, helping them survive even when humans change the land.
The authors of the study also found that due to activities such as farming, deforestation and infrastructure development, human-dominated habitats could be losing their unique bird species and ending up with the same kinds of birds in terms of species diversity, ecological functions and phylogenetic clustering patterns.
Co-author Hari Prasad Sharma, associate professor at Central Department of Zoology, Tribhuvan University, said that in the study area, anthropogenic pressures in fragile landscapes have pushed bird communities toward reduced resilience and increasing homogenization.
In terms of species diversity, the study found that natural habitats had little “nestedness,” indicating they may not have lost many species and had their own unique mix of species. But in human-modified places, high nestedness suggested loss of many species and supported the notion that the surviving ones were just a subset of birds found in healthier, more natural areas.
The study found that in natural habitats, in terms of function and evolutionary traits, natural habitats support many species that perform a wide variety of ecological roles (such as eating insects, dispersing seeds) and come from diverse evolutionary lineages. But settlements and other human-altered areas have far fewer species, fewer ecological roles and simpler bird communities.
Katuwal said the study found that forests offered significant habitats for distinct bird species such as collared scops-owls (Otus lettia) and Western hooded pitta (Pitta sordida) that were rare in other habitats.
In terms of community assemblage and clustering patterns, researchers found strong functional clustering among birds in human-dominated habitats, hinting that the birds share similar ecological roles or traits. This, according to the study, suggests that heavy human disturbance acts like a filter only allowing birds such as pigeons, doves, mynas and crows that can tolerate people to survive. In contrast, natural habitat mosaics provide space for birds with different ecological roles and traits, reducing functional clustering.
The study also threw up an unexpected result. Phylogenetic clustering, a measure assessing the proximity of species that remain in an area in the evolutionary family tree, was found to be strongest in natural habitats, especially forests, even though the researchers expected the opposite.
The most likely reason is that human activities, even inside forests, remove the more sensitive bird species, the authors said. This leaves behind groups of birds that are closely related and tough enough to handle disturbance, such as flycatchers, babblers and warblers. These birds survive because they share similar traits and adaptations that help them live in the same kinds of environments, according to the study.
Sangeet Lamichhaney, associate professor at the Department of Biological Sciences, at Kent State University in the U.S., said he agrees with the findings of the study. Lamichhaney, who wasn’t involved in the study, said landscape heterogeneity also provides a wider range of food resources, nesting sites, microclimates and shelter opportunities, allowing different species with different ecological requirements to coexist.
“Heterogeneous habitats also help birds adapt to environmental change by offering alternative resources or refuges when one habitat type becomes degraded,” Lamichhaney said.
The study’s findings are important, as they show that when forests are conserved, bird species thrive, increasing the potential for other species to occur and coexist, Sharma said. These findings also suggest that Important Biodiversity Areas (IBAs) should be maintained with national priority forests managed properly with the community people’s participation.
The most important step, Lamichhaney said, is protecting and restoring habitat quality by controlling deforestation, regulating sand and gravel extraction and preventing unmanaged road expansion.
“Strengthening and reconnecting habitat corridors, particularly along river systems and forest ridges, is essential for maintaining metapopulation connectivity and ensuring that birds can move freely in response to seasonal needs and environmental stressors.”
Banner image: Lesser adjutant fledglings in the Parsa-Koshi Complex. Image courtesy of Hem Bahadur Katuwal.
Citation:
Katuwal, H. B., Bhattarai, B. P., Regmi, S., Nepali, A., Kc, S., Gautam, R., Rokka, P., Pradhan, N., Koirala, S., Mandal, D. N., Sharma, H. P., & Quan, R. (2025). Anthropogenic pressures drive the multidimensional homogenisation of bird diversity in a South Asian landscape. Journal of Environmental Management, 394, 127628. https://doi.org/10.1016/j.jenvman.2025.127628
As Kathmandu’s birds get used to humans, biodiversity suffers, studies show
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