Lonely Old Deers: Ageing Red Deer become less social as they grow old
New social network analysis of wild red deer in the Isle of Rum, Scotland, shows that ageing deer tend to adopt a life of solitude as they reach their elderly years.
A multidisciplinary team from scientists at the Universities of Oxford and Edinburgh has revealed that wild red deer become less sociable with age.
Dr Greg Albery, lead author of the study and currently a Postdoctoral Fellow at the University of Oxford said:
We found that deer’s social networks shrink as they grow old and begin associating less with others. This ‘social ageing’ appears to be driven by older individuals choosing to live in more isolated locations, and engaging with fewer other deer within these sparser areas.
Building a general understanding of how individuals change their social behaviour as they age is useful for research across many different species, including humans. Such research sheds new light on the consequences of senescence for ageing individuals, as well as potentially providing insights into how societal structure and function might change as the population ages.
The team applied novel social network analysis methods to a large, 43 year long, dataset made up from over 200,000 census observations of >3500 female deer over their lifetimes.
As deer grow older, they begin to interact with less other individuals within their home ranges. They also shift their locations to less populated areas of their habitat.
Alongside becoming less central in the social network, older individuals were generally found with smaller home ranges, farther from the centre of the population, in areas of lower density, and with lower-quality grazing.
Josh Firth, a Research Fellow at Oxford University and senior author on the study said:
This new evidence of social ageing in the wild shows the value of long-term datasets. By tracking many individuals simultaneously over their entire lives, we can understand how and why their social associations with one another change over time.
While earlier work has shown that older wild animals in other species may be less sociable than younger animals, it was previously difficult to determine whether this was due to demographic changes or to more sociable individuals dying sooner. However, using this long-term dataset, the new research shows that social ageing happens at the individual-level, where individuals actively become less sociable throughout their lives.
The research also highlights that further work is now needed to understand exactly why ageing deer become less social. The authors suggest this social ageing may be due to a combination of many factors, such as moving to areas that are easier for older individuals to forage in, or changing their behaviour to become more ‘socially selective’ with whom they associate with.
Dr Albery added “Combining social networks with spatial data allowed us to disentangle the potential causes of these age-related declines in social behaviour, and to show how individuals change their behaviour over the course of their lives.”
The researchers now hope that bringing these scientific approaches to other long-term data sets of wild animals will help generate a broader view of the fundamental rules that may govern ageing and social behaviour in natural populations.
To read more about this research, published in Nature Ecology & Evolution: https://www.nature.com/articles/s41559-022-01817-9