Because bird identification guides and mammal encyclopedias usually show images of animals as either “adults” or “juveniles,” we tend to think of other living beings in only these two stages of life.
If you look at almost any bird identification guide or mammal encyclopedia, you’ll typically see two to three images of any one animal: an adult female, an adult male and, perhaps, a juvenile.
That’s extremely helpful if you’re trying to identify a being you see in the wild; but like us, nonhuman animals, in reality, live not only in two ages but in a range of stages of life and social proclivities. And, I think, we’re just beginning to appreciate that fact because a few new studies are demonstrating that humans are not the only animals to change their social behavior as they age.
Red deer
Red deer may become less sociable as they grow old to reduce the risk of picking up diseases, concludes researchers from England’s University of Leeds, who published their study in October 2024 as part of a special issue of the journal Philosophical Transactions of the Royal Society B. This special issue is an international collaboration and looks at how individuals of different species age, how this shapes their social interactions and what this means for their societies across the natural world.
Wild animals—such as red deer—provide a good model for studying the benefits and costs of changing social behavior with increasing age.
Using data from a long-running project tracking a wild herd of red deer on the Isle of Rum in Scotland’s Inner Hebrides, the University of Leeds scientists showed that as older female red deer become less and less social with age, they cut down on competition and reduce their risk of parasitic infections.
While previous research has often considered the process of becoming less social with age—known as “social aging”—as potentially negative, this study shows that changing habits could, in fact, bring benefits. Like older humans who scale back their social interactions to avoid infections such as COVID-19, the less sociable, older does are less likely to pick up certain diseases.
In the wider view, say the researchers, animal populations are a great way of considering the fundamental rules of how aging may shape societies—even ours. Because aging is a universal process and all animals live in some sort of social context, the topics the researchers discuss in the Philosophical Transactions of the Royal Society B special issue can have far-ranging implications. The hope is that in understanding the diversity of aging and sociality across lots of different species, we’ll gain insights on the processes governing our own society at a time when understanding aging is particularly important. According to the United Nations, virtually every country in the world is experiencing growth in the number and proportion of older persons. By 2050, one in six people in the world will be over age 65, up from one in 11 in 2019.
A new study suggests that red deer avoid social interactions as they age because they become more vulnerable to the costs of infections.
House sparrows
Even a common garden bird, the house sparrow, changes its social behavior as it ages, according to another paper in the Philosophical Transactions of the Royal Society B special issue. It’s one of the first to suggest that birds, like mammals, also reduce the size of their social networks as they age; specifically, the number of friendships that they have and their standing in the wider social network.
The house sparrow study was led by researchers at the Imperial College London, who have been conducting a long-term house sparrow study on the English island of Lundy. With no sparrows either arriving in the remote island population or leaving it, researchers can monitor the whole population from birth to death and everything in between in exceptional detail.
Their findings, say the researchers, may be driven by existing friends of the same cohort groups dying as they age and because it takes more effort for older birds to make friendships due to fewer same-age individuals available to bond with. Conversely, the benefits of social connections may be lower than they are for younger individuals, who may come to rely on those connections for things like information or reproduction later in life.
Like us, older house sparrows seem to have fewer social interactions as their peers die off.
The house sparrow study reveals interesting patterns, say the scientists, showing that females and males can respond differently, that the social environment during development or adulthood can have different impacts, and that the age of social partners is important.
Both the red deer and house sparrow studies show that animal systems are now well placed for developing a fundamental understanding of aging societies and why social aging happens, which could eventually lead to new interventions to support healthy aging in humans.
Vultures
If you’d rather be watching TV on your couch than dancing at the club, say some scientists from the University of California, Los Angeles (UCLA), you might have something in common with aging Eurasian griffon vultures (Gyps fulvus). Their new research shows that young griffon vultures move frequently between sleeping sites in different locations and interact with many friends but get set in their ways as they grow older, roosting in the same spots with the same individuals. As schlepping between roosts becomes a grind, older vultures follow the same path, establishing movement routines that are not seen in young vultures.
The Eurasian griffon vulture is the most populous and social of Europe’s four vulture species, feeding in groups and roosting in large colonies of hundreds of individuals. Following a 20th-century decline due to decreasing food supplies, hunting and poisoning, today there are about 35,000 breeding pairs.
Younger vultures shy away from the most popular roosts, suggesting they might be intimidated by the older vultures or that there’s a vulture equivalent of “Hey, you kids, get off my lawn,” conclude the UCLA researchers, who published their paper in the Proceedings of the National Academy of Sciences in August 2024. They show that like many older people, elderly vultures tend to have fewer, more selective friendships with stronger bonds. The birds may also have a more thorough knowledge of where to find food resources.
Eurasian griffon vultures are large vultures that live in India, the Mediterranean region and the Middle East. With wingspans up to nine feet, they’re much larger than North American turkey vultures and bigger than bald eagles.
Finding food can be tricky for vultures because it depends on locating animal carcasses—an unpredictable and ephemeral source. When Eurasian griffon vultures find a carcass, they tend to sleep or roost nearby and feed on it over a period of days. Roosting sites can thus be “information hubs,” where vultures that recently fed signal to others about food sources; they then follow each other to carcasses and form friendships that help them stay in the loop about food.
Older vultures may have a more thorough knowledge of where to find food resources and less need to learn about them from other vultures at busy roosts.
The UCLA researchers set out wanting to know if an individual griffon vulture’s movement patterns and social behavior changed over the course of its life. They used GPS data from 142 individually tagged birds in Israel to cross-reference the vultures’ ages with their movements and social interactions at roost sites.
It was found that as they age, the vultures’ loyalty to certain roost sites increases. Young vultures check out many different roosts; but in middle age, they start going repeatedly to the same places.
The study showed young vultures sometimes returned to the same roost but usually chose different ones, rarely spending two nights in the same place. From young adulthood at around five years old through middle age, they spent about half their nights at the same “home” site and half elsewhere. In old age, they became true homebodies.
The number of individuals vultures interacted with didn’t change with age; if they had three friends when young, they still had three when older. But the amount of time they spent with vultures outside of their close-friend group plummeted.
When the vultures are old (from the age of 10 onward), say the researchers, they no longer have the energy to be out and about, and they return consistently to the same site. Even those who were adventurous at the age of five became more sedentary by age 10.
As the vultures grew older, the strength of their social bonds decreased, as well, for at least part of the year. The number of individuals they interacted with didn’t change with age; if they had five friends when young, they still had five when older. But the amount of time they spent with vultures outside of their close-friend group dropped dramatically. Older vultures spent most of their time with and roosted mostly with these close friends. Their movements also became more routine, eventually following a predictable pattern.
The study is unique because the researchers were able to track the movements and social behaviors of the same vultures for up to 12, nearly consecutive years over a 15-year period. They were able to show that the trends of individuals becoming more loyal to the same sites with age is not because the more exploratory individuals die earlier and live shorter lives, and the older, more sedentary individuals live longer. Individuals change their behavior with age, and this has rarely been shown in nature for long-lived birds due to the difficulty of tracking individuals for such an extended period of time.
Individual vultures change their behavior with age. A new study demonstrates this and is notable because that’s rarely been shown for long-lived birds in nature due to the difficulty of tracking individuals for such a prolonged period.
The research backs up findings from studies in other species that, with age, animals become more faithful to their known routines and sites—and potentially become more selective in their social relationships. These behaviors are commonly attributed to aging in humans and can help improve understanding of how animal populations move about in their environments and relate to other members of their species, as well as identify better ways to protect them from threats. For Eurasian griffon vultures, this could mean better protection of important roosting sites and using knowledge about their social interactions to reduce the risk of poisoning.
Humans
It’s clear that many nonhuman animals experience aging similar to how we do, and, as a result, they provide an excellent opportunity to study a natural process that most living beings go through.
Some nonhuman animals experience aging like we humans do; and, as a result, provide an excellent opportunity to study a natural process that most living beings go through.
But even more than providing a chance to study a common life course, learning more about the social aspects of aging in nonhuman animals also, I think, puts them on the same plane as us.
For they are, after all, our equal, fellow travelers on planet Earth.
Here’s to finding your true places and natural habitats,
Candy
