Human-driven changes to landscapes, such as urbanization and agricultural expansion, are reducing the ecological services provided by wild birds, according to a new global study. Researchers analyzed data from nearly 3,700 bird species across 1,200 sites worldwide and found that habitat modification leads to fewer species performing essential roles like pollination, seed dispersal, and predation.
This reduction in what scientists call "functional redundancy" means that fewer species are available to back up these roles if others decline or disappear. In natural environments, multiple species often perform similar ecological functions, which helps ecosystems remain stable during disturbances.
The findings were published in the journal Nature. Using computer simulations of extinction events, the research team demonstrated that land-use change removes this buffer effect and leaves ecosystems more vulnerable to further biodiversity loss.
Thomas Weeks, a PhD student at Imperial College London and lead author of the report, stated: “The decline in bird diversity after land-use change is well known, but until now it was generally thought that enough different types of birds survived for those degraded ecosystems to continue functioning as required. Our analyses challenge that idea by showing that humans modify landscapes in a way that tends to remove all the slack in the system, meaning that any future environmental shocks can potentially cause a collapse of the essential services provided by wildlife.”
Professor David Edwards from the University of Cambridge’s Department of Plant Sciences and Conservation Research Institute added: “A variety of bird species play key roles in supporting the ecosystems that we rely on, yet we are damaging habitat quality and thus the potential for species to fulfil their critical roles. It’s time that more is done to safeguard the future of biodiversity."
By examining characteristics such as diet, body size, beak shape, and wing shape among bird species, researchers assessed how birds contribute to ecosystem functions. They found disturbed habitats are often dominated by a few disturbance-tolerant species occupying similar niches. This results in lower overall functional diversity and leaves some key ecological roles unfilled.
Such simplification can have cascading effects on forests' ability to regenerate naturally, reduce carbon storage capacity in vegetation systems globally (https://www.nature.com/articles/s41586-025-09788-0), and increase crop pest populations.
The study also highlights that even when there appears to be high numbers of bird species present ("species richness"), losing functional redundancy still exposes ecosystems to greater risks from global environmental changes—a pattern observed worldwide from tropical forests to polar regions.
Senior author Professor Joseph Tobias from Imperial College London commented: "With land-use change accelerating worldwide, our study highlights the urgency of managing and preserving functional diversity to ensure that future ecosystems continue to function in ways that help support human life and economic stability."
The research introduces a framework for evaluating ecosystem fragility aimed at guiding conservation policies. By focusing on vital ecological roles played by different species within an ecosystem rather than just counting total numbers or types present—policymakers may better identify risks and work toward maintaining both wildlife populations and broader ecological stability.
Reference: Weeks TL et al., ‘Land-use change undermines the stability of avian functional diversity.’ Nature (November 2025). DOI: 10.1038/s41586-025-09788-0