- Cities are now home to wildlife like foxes, parrots, monkeys, raccoons, boars, and countless bird species, which are not temporary visitors, but permanent urban residents.
- If we want to support their long-term survival, we need to understand how urban environments shape them at every level, from behavior to bacteria, and this includes their gut microbiome, which shapes behavior and other factors.
- “The microbiome is not a niche scientific curiosity, it is a biological system that influences how animals eat, think, move, and cope with stress. And in a rapidly urbanizing world, it may be one of the most important and overlooked tools we have for understanding how wildlife adapts to human-dominated landscapes,” a new op-ed argues.
- This article is a commentary. The views expressed are those of the author, not necessarily of Mongabay.
Cities are expanding faster than at any point in human history, and wildlife is adapting in remarkable ways. We often talk about visible changes like animals becoming bolder, shifting their diets, or altering their daily rhythms to avoid people. But there is a deeper transformation happening inside their bodies, one that conservation science has barely begun to address: The reshaping of the gut microbiome.
Urban ecosystems expose animals to a completely different set of pressures than their natural habitats. Artificial light, chronic noise, pollution, and human-derived food sources all interact to shape the physiology of wildlife rapidly. These pressures don’t just influence behavior from the outside, they alter the microbial communities that regulate digestion, immunity, stress responses, and even cognition, making key components of how animals evolve and adapt as “pressure cookers,” reducing diversity and decreasing overall health.
When the microbiome becomes disrupted, a state known as dysbiosis, animals may become more anxious, more risk-taking, or more susceptible to disease. Urbanization is forcing this rapid adjustment of species not just through habitat loss, but by fundamentally changing their microbiota, and with that, things like foraging patterns and predator avoidance. In other words, urbanization may be shaping wildlife behavior from the inside out.
Yet conservation strategies rarely consider this internal dimension. We focus on green spaces and habitat restoration, which are essential, but overlook how environmental stressors affect the microbial health of the animals we are trying to protect. If animals such as foxes, raccoons, or cockatoos appear to be adapting well to cities, we often assume it is thriving. But a stable population can still be experiencing chronic physiological stress that only becomes visible years later.
Take birds, for example. Many species readily exploit human food waste, which is calorie rich but nutritionally poor, instead of a fiber-rich diet, which is good for bacteria to ferment and promotes good gut function. This shift in diet can alter gut bacteria, affecting immunity and long-term health, while constant noise pollution that elevates stress hormones can do the same. These internal changes may not be obvious in the short term, but they can accumulate across generations.
Understanding these hidden mechanisms could help conservationists design strategies that directly support healthier wildlife populations. Reducing light pollution, managing waste more effectively, and creating microhabitats with natural food sources are not just aesthetic improvements, they become interventions that stabilize the microbiome and improve its resilience.
Recognizing that wildlife health is multidimensional and that the microbiome is a crucial part of that picture is the next step in conservation, as it has always evolved when new science emerges. We once ignored behavior, for instance, then realized it was essential, then advanced into genetics, and now, the microbiome is the next frontier.
Cities are now home to foxes, parrots, monkeys, raccoons, boars, and countless bird species. These animals are not temporary visitors, they are becoming permanent urban residents. If we want to support their long-term survival, we need to understand how urban environments shape them at every level, from behavior to bacteria.
The microbiome is not a niche scientific curiosity, it is a biological system that influences how animals eat, think, move, and cope with stress. And in a rapidly urbanizing world, it may be one of the most important and overlooked tools we have for understanding how wildlife adapts to human-dominated landscapes.
Conservation begins with seeing the full picture. It’s time we look inside.
João Guerreiro is a biochemist focused on the gut–brain axis and microbiome who is currently completing a master’s degree in neuroscience at the University of Lisbon in Portugal.
Banner image: Sulphur-crested cockatoo on a street lamp in Bondi, Sydney, Australia. Image by Sardaka via Wikimedia Commons (CC BY 2.0).
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