Summary: New research on zebra finches reveals that stress spreads within social groups, even affecting individuals not directly exposed to stressors. Birds in groups with more stressed members showed reduced movement and changes in social behavior, such as fewer social bonds. This contagion effect can impact resource access and group cohesion, suggesting stress in one individual can have far-reaching consequences.
The findings highlight how environmental challenges, like urbanization and climate change, may ripple through animal communities. Such stress contagion could reshape group dynamics and individual fitness, affecting survival and reproduction.
Key Facts:
- Stress spreads to group members who have not experienced the initial stressor, reducing activity and altering behavior.
- Stressed groups have weaker social cohesion, with unexposed members relying on fewer, stronger social bonds.
- Lower activity among unexposed group members may limit resource access, affecting survival in the wild.
Source: University of Konstanz
Animal habitats are currently changing extremely rapidly and extensively due to urbanization and climate change. As a result, animals are increasingly exposed to stressors.
However, until now, little research has been conducted on how individual stress levels affect the group and the behaviour of other group members that may not have experienced a stressor themselves.
Hanja Brandl, a behavioural biologist from the Cluster of Excellence Collective Behaviour at the University of Konstanz, and her colleague Damien Farine (now at Australian National University) conducted experiments with 96 zebra finches.
Their aim was to find out whether and how the stress responses of individual birds affect other members of their group.
In three rounds of experiments lasting four weeks each, some members of groups of zebra finches were exposed to different disruptions resulting in stress.
Cameras then recorded in fine detail how stress affected the behaviour the exposed individuals and—importantly—how these changes in turn affected the behaviour and reproduction of other members of the group that had not experienced the disruptions.
In addition to this, the researchers measured the level of the stress hormone corticosterone in the animals’ tail feathers.
Stress is contagious
“Our experiments show that stress responses can spread beyond individuals to other members of their social group, even to those who are not exposed to stress themselves”, Hanja Brandl says.
“In groups where a larger proportion of birds experiences stress, we observed this effect even more strongly”.
The social environment impacted both the activity and the social behaviour of the zebra finches that had not experienced stress. Their response was similar to that of the zebra finches that had experienced stress.
The researchers observed that unexposed birds in groups that had a large proportion of its members experience stress moved less.
“For birds in the wild, this reduced level of activity could, for example, mean that they explore their environment less and limit their range of movement, which, in turn, means that they could have access to fewer resources”, Brandl explains.
The experiment also showed that the presence of stress-exposed group members altered the social behaviours of other group members. Individual birds that were not exposed to the stressor maintained fewer social bonds and tended to rely more heavily on existing relationships.
“This means that stress in a group could impact its social cohesion. At the same time, a reduction in weak social ties would, in turn, reduce the risk of stress transmission”, Damien Farine says.
Thus, stress transmission can have profound effects on both the dynamics of social groups as well as the fitness of individual members.
About this social neuroscience and stress research news
Author: Helena Dietz
Source: University of Konstanz
Contact: Helena Dietz – University of Konstanz
Image: The image is credited to Neuroscience News
Original Research: Open access.
“Stress in the social environment: behavioural and social consequences of stress transmission in bird flocks” by Hanja Brandl et al. Proceedings of the Royal Society B Biological Sciences
Abstract
Stress in the social environment: behavioural and social consequences of stress transmission in bird flocks
The stress response helps individuals cope with challenges, yet how individual stress levels shape group-level processes and the behaviour of other group members has rarely been explored.
In social groups, stress responses can be buffered by others or transmitted to members that have not even experienced the stressor first-hand. Stress transmission, in particular, can have profound consequences for the dynamics of social groups and the fitness of individuals therein.
We experimentally induced chronic stress within replicated colonies of zebra finches and used fine-scale tracking to observe the consequences of stress-exposed colony members for the behaviour and reproduction of non-manipulated colony members.
Non-manipulated individuals in colonies containing stress-exposed individuals exhibited reduced activity, and fewer—but more differentiated—social bonds.
These effects were stronger in colonies with a greater proportion of stress-treated individuals, demonstrating that the impact of stressors can reach beyond directly exposed individuals by also affecting their group mates.
We found no evidence that socially transmitted stress affected reproduction or long-term physiological measurement in unmanipulated birds, even though the stress-exposed demonstrators laid slightly fewer eggs and showed stressor-dependent changes in feather corticosterone. Social transmission of these effects, if occurring at all, might be more subtle.
