Urban Environments Change Animals' Social Skills! The "Non-Human Residents" of the Concrete Jungle — Urbanization Takes More Than Just Their Nests

Urban Environments Change Animals' Social Skills! The "Non-Human Residents" of the Concrete Jungle — Urbanization Takes More Than Just Their Nests

Cities are "devices" that accumulate convenience for us humans. However, other creatures experience the same city as "a place where the noise never stops," "a place where the night never ends," and "a place with few hiding spots." The impact is not limited to the types of food or nesting locations. Who they meet, how they send signals, the sense of distance in living, falling in love, and raising offspring—essentially, the very "way of society" can change.


This point was significantly expanded by an international review study conducted by researchers at Bielefeld University in Germany. They aimed to systematically map the impact of urbanization on animal social behavior, not as individual cases but as a comprehensive overview. The study reviewed 227 papers, and the conclusion was quite strong. It reported that 92% of the studies found that urbanization "significantly affects" animal social behavior.


"Urban Stress" Penetrates Animal "Relationships"

Animals living in cities face not isolated challenges but a combination of factors: traffic noise, artificial light, reduced vegetation due to buildings and pavement, lack of hiding places, chemical pollution, and proximity to humans. These factors overlap and gradually distort daily decisions.


Social behavior includes all interactions between individuals, such as cooperation, competition, maintaining groups, territorial disputes, courtship, and parenting. Therefore, changes in social behavior directly affect survival strategies like "can they reproduce," "can they secure food," and "can they avoid predators." Small discrepancies in urban areas can reverberate across generations, affecting population numbers and distribution.


Noise is the Most Studied—But There's a Significant Bias

The review highlights two important points.


One is that the impact of urbanization is widespread. Changes in social behavior often manifest as "communication disruptions," "changes in aggression levels," and "changes in group (collective) stability."


The other is the significant bias in research. Among urban stresses, noise is particularly well-studied. The reason is straightforward. Birdsong, alarm calls, and courtship sounds—communication that relies on sound is easily observed when drowned out by low-frequency, continuous noise from cars and machinery. For example, birds may be forced to change the frequency or timing of their calls, or the efficiency of communication may decrease. This can lead to social outcomes such as "success rates in courtship" and "frequency of territorial conflicts."


However, the focus on noise means that other factors like light pollution, chemical pollution, and new encounters between species (contact created by urban "density") are not yet fully understood. For instance, artificial light at night can shift activity times, change potential mates or competitors, and even affect the seasonality of reproduction. Yet, comprehensive comparative studies on these aspects are still insufficient.


The Issue of Focusing Mainly on Birds—The More Common "City Regulars" Are Less Visible

A particularly symbolic aspect of the review is the bias in research subjects. Studies are concentrated on birds, which adapt easily to urban environments and are easy to observe, accounting for about 62% of the total. In contrast, insects, reptiles, and even small mammals, which are increasing in number in urban areas, are relatively underrepresented.


There are two risks here.
First, generalizing the impact of urbanization based on what is visible in birds. The way urban stress "penetrates" may differ between birds, which rely heavily on sound communication, and insects and mammals, which rely on smell, touch, and subtle vibrations.


Second, smaller creatures that play crucial roles in urban ecosystems are more likely to be overlooked in urban design discussions. The design of urban green spaces and waterfronts should be evaluated not just for aesthetics but also for their function as hiding places, movement corridors, and breeding sites. However, there is a lack of fundamental data to assess these functions.


Moreover, studies directly addressing interspecies interactions (such as "piggybacking on the alarm behavior of other species," "species competing for feeding grounds," and "sharing resources created by humans") are quite few in the review. Cities are inherently places where "new neighbor relationships" between species are likely to form. If this remains unexplored, we may misinterpret the social reorganization occurring in urban areas.


When Society Changes, Reproduction Changes—The Future of "Unraveling Flocks"

Changes in social behavior do not end with interesting "behavioral diversity." Weakening of group cohesion, changes in hierarchy or territorial rules, shifts in courtship strategies, and breakdowns in cooperative parenting—such changes can affect reproductive success. In cities, invisible bottlenecks like "there is food, but it's not safe to raise young" or "there is a mate, but signals don't get through" can occur. Signs of "social fraying" may appear before a sudden population decline.


Conversely, cities can also become "experiments in adaptation." New social systems that "fit" urban environments may emerge as different courtship strategies are chosen under noise or the form of groups changes. However, whether this is beneficial for species survival in the long term or merely a short-term adjustment is still uncertain. This is the most challenging and crucial point for conservation and urban planning.


From "Human Cities" to "Habitats for Multiple Species": The Homework for Urban Planning

The review study goes beyond biology. Its message is directed toward the future vision of cities: "Future cities should not be designed solely for humans but as habitats."


So, what can be done specifically? The key is not to "eliminate stress" but to "increase escape routes and options."

  • Sound: Green buffers along roads, revising structures that create noise peaks, and limiting nighttime construction.

  • Light: Illuminate only where necessary, consider color temperature and angle of illumination, and preserve dark corridors.

  • Habitat: Networks of small hiding places like plantings, soil surfaces, leaf litter layers, and microtopography of waterfronts.

  • Fragmentation: Connect green spaces not as "dots" but as "lines."
    Such measures not only protect animals but also relate to urban ecosystem services mediated by insects and small animals (pest control, seed dispersal, decomposition, etc.). Consequently, they also enhance human living comfort.


Reactions on Social Media (Trends and "Common Discussion Points")

This topic tends to evoke surprise and agreement on social media as it delves deeper into the image of "animals adapting to cities = resilient." The following points are particularly likely to be shared.

  • "It's striking that it's not the personality that changes with the environment, but the 'way of relating.'"

  • "Communication disrupted by noise and light is a story similar to humans, after all."

  • "I understand why it's mostly about birds. What about insects, mice, and reptiles?"

  • "Aren't human actions like feeding and waste management increasing 'urban stress' too?"

  • "The argument that urban planning should shift from 'human-centered' to 'including ecosystems' should spread more."


※ The above is an organized collection of typical reaction patterns when this theme spreads (examples for introduction). Often, discussions do not fully take off immediately after release, and more discussion points emerge as perspectives from researchers, local governments, and urban residents mix.


Summary: Urbanization Changes "Relationships," and Relationships Change the Future

When discussing the impact of urbanization on animals, we tend to focus on "can they live there/can't they" and "increase/decrease." However, what lies before that is "how they relate." Communication, aggression, group stability, courtship, parenting—if society wavers, so do reproduction and survival.


The review of 227 studies clearly demonstrated that cities significantly alter animal social behavior. However, insights biased towards birds and noise cannot fully capture the "society" of diverse urban creatures. What is needed now is research on more taxonomic groups, complex stresses, interspecies relationships, and studies "translatable into urban planning."


Will future cities remain cities just for us? Or will they evolve into habitats where multiple species can "have societies" and live? The answer will be determined not only in laboratories but also in the design of city lights, sounds, and greenery.


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