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  • Brogan Stewart

Monkey Disability and the Quest for Behavioral Complexity

Updated: Mar 8, 2023


Japanese macaque (Macaca fuscata) named Chonan with congenital limb malformation eating sweet potato at Awajishima Monkey Park. Photo Credit: Brogan Stewart

How does disability affect monkeys in the wild?

Does the complexity of a monkey’s environment determine how complex its behaviour can be?

For my PhD research, I am investigating how Japanese macaques – also known as snow monkeys – respond behaviourally to physical condition and environmental context. Like most projects in the Zooentropy sphere, I’m doing that by examining behavioural complexity using fractal analysis.

Fractal analysis provides a mathematical framework for examining, among so many other things, animal behaviour. It helps us detect subtle changes in behavioural complexity and will help give us insight into these challenging questions I posed at the top.

For more information on complexity in animal behaviour patterns, browse this Zooentropy website.

As for me, I began my research in 2019, at the Awajishima Monkey Centre (AMC) on the island of Awaji in Japan. The Japanese macaques that live in this mountainous forest are free-ranging, which basically means that they are wild but are provision-fed by the AMC staff and by tourists who visit the center. The AMC is run by owners Mr. and Mrs. Nobuhara (check out her Instagram feed here).

The monkeys on this island are unique, where a relatively high proportion of them (around 16%) are born with malformations. These disabilities range from fused fingers to missing hands and feet. Many of the disabled individuals in this group have long lives and can keep-up with the movements of the group. But they may still face various challenges, both known and unknown to us.

Japanese macaque (Macaca fuscata) named Ribbon at Awaji island with congenital limb malformation. Photo Credit: Brogan Stewart.


Japanese macaque (Macaca fuscata) named Monmo at Awaji island with congenital limb malformation. Photo Credit: Brogan Stewart.


Here’s a fun story about some work done by my PhD supervisor, Dr. Sarah Turner, on these Awajishima macaques:

I am visiting the AMC this summer, 2022, for additional behaviour data collection. I am comparing disabled monkeys with non-disabled controls to identify whether the disabled individuals are experiencing differences in their behavioural complexity signatures.

“Complexity signature” is just a term we use to describe a sequence of behaviour produced by an individual monkey. It’s a useful analogy because, like real signatures, each monkey’s sequences of behaviour might produce patterns unique to itself. And that’s something I’m looking for in my data.

If complexity signatures are pretty much the same between disabled and control monkeys, that could indicate that disabled individuals have grown accustomed to their disabilities. On the other hand, if the signatures are much different, that could indicate that they are potentially experiencing higher stress levels than nondisabled individuals, or that their behaviour may be somehow less efficient than control animals.

This is an important question. It can give us insight into the behavioural plasticity of animals in response to disability. This could help us better understand injury and illness, which are key features in animals’ lives in the wild.

In 2020, I also collected behavioural data on the captive Japanese macaques at the Zoo de Granby in Granby, Quebec, Canada. These monkeys have lived in captivity their whole lives, are well-fed in a nice enclosure, and are given some environmental enrichment. This year, I will collect samples from Japanese macaques in other captive conditions to be able to compare the behavioural complexity between the different groups in different environments.

Japanese macaques (Macaca fuscata) named Ionka and Zoe groom at Granby Zoo, Granby, Quebec.


I hope to compare the behaviour of captive Japanese macaques with that of the free-ranging group at the AMC and to a wild population on Yakushima, Japan. I am interested to see if the monkeys in different environmental contexts display a range of behavioural complexity signatures that can somehow be linked to those conditions.

Specifically, I’m curious to know whether the Japanese macaques display less behavioural complexity as their external environment decreases in heterogeneity, as would be the case in captivity.

Complexity in, complexity out.

This research is important because it will help inform our understanding of the behavioural complexity signatures needed for macaques in captivity to live more natural lives. Investigating differences caused by variation in environmental heterogeneity can also contribute to improving captive animal welfare by indicating what degree of environmental enrichment is needed, and as a possible application to monitor stress levels over time.

At the core, I’m really interested in how animals respond to change.

In addition to this work with Andrew MacIntosh and Zooentropy, I also study behavioural changes of primates in response to human-induced climate change. I am presently investigating whether the diurnal activity budgets of Japanese macaques have shifted in response to current climatic changes. My past work analyzed potential primate habitat shifts in response to cumulative carbon emissions.

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