Antwerp ZOO’s research staff spent an impressive 430 hours observing the zoo’s owl-faced monkeys and gorillas as the animal experts prepared these two primate species to share an enclosure. ‘This is one of the most significant behavioural observation projects we have ever conducted’, explains Animal Welfare Research Coordinator Marina Salas. ‘Thanks to the vast amount of information we’ve collected, experts from all disciplines can collaborate in a scientifically substantiated manner. We can make predictions about improvements to the animals’ wellbeing in the run-up to their actual cohabitation.’

It takes a great deal of preparation before two species of animals can share an enclosure. Curator Sarah Lafaut explains: ‘Carefully considered mixed enclosures are the future, and we are seeing this more and more often in our zoos. The natural behaviours ensuing from such cohabitation have a favourable effect on social species. Just as in the wild, co-housing will enrich the lives of both the owl-headed monkeys and the gorillas and promote their general wellbeing.’ She continues: ‘In theory, these two primate species are very compatible. But how will this work out in practice, in our zoo? To find out the answers, behavioural observations like these are invaluable.’

“Theory is one thing; putting it into practice is another. To find out the answers, behavioural observations like these are invaluable!” - curator Sarah Lafaut

Hours of watching

It was definitely a marathon, not a sprint: two students from different university colleges spent nine months observing the owl-faced monkeys and gorillas via the ZOOmonitor app between September 2023 and May 2024. During this period, the owl-faced monkeys were moved into the Primate Building to allow them to become better acquainted with their future neighbours while still safely separated by a glass wall and to explore the large outdoor enclosure, as a first step towards cohabitation. Marina Salas: ‘We observed the behaviour of each owl-faced monkey for 50 hours. For three animals, that comes to 150 hours. The gorillas took even more time: 57 hours of observation per gorilla meant 280 hours in all.’ According to post-doctoral researcher Jonas Verspeek, the zookeepers also contributed to the project. ‘During the same period, they spent many hours in their turn observing the animals via the Akongo App, which uses a principle called the Akongo Welfare Assessment. In addition to behaviour, this application also takes a wealth of other indicators into account and works on the basis of streamlined questionnaires.’

During their lengthy observations, the scientists investigated various aspects. ‘Our primary concern is clear: how will moving the owl-headed monkeys into the gorilla enclosure affect behaviour and social dynamics among the two species? In concrete terms, we are examining what is referred to as an “activity budget” based on a number of key indicators. What activities can be observed, and how are these organised in terms of ratio and frequency? In what parts of the enclosure do the the animals perform which activities? Do they move about a lot, how are their eating habits, are they displaying natural behaviour? In addition, we are specifically interested in any stress-related reactions and their frequency. We are also compiling a “social networking analysis” and observing which animals prefer to be in proximity to one another, the sizes of these groups and if they interact with one another.’

“Nothing” to see, lots to do

Marina Salas is excited about the preliminary results: ‘In general, we saw relatively few changes in both species’ behaviour prior to their introduction to one another. Which is great news! Our greatest hope was that there would be no increase in negative reactions. The gorillas have noticed that the owl-faced monkeys have moved into their enclosure, but are not moving about more frequently than otherwise, including for stress-related reasons. The owl-faced monkeys are huddled more closely together and are a lot more active, which may be attributed to the fact that they now have an outdoor enclosure at their disposal as well. The difference is clearly more pronounced for them, as confirmed by our observations of their behaviour.’

According to Jonas Verspeek, observation is only a first step. ‘It has always been our intention to monitor the wellbeing of these animals. The next step is to set to work with the data – the output – we have obtained. We want to do everything in our power to ensure that cohabitation in a mixed enclosure enhances the wellbeing of both primate species. As a preventive measure, we will be placing a few puzzle boxes in the enclosure to keep the gorillas occupied and distract them from the owl-faced monkeys exploring their new enclosure. Observation has shown that this helps. Our actions can also be reactive. If we notice any stress building up, we will adapt the situation accordingly. The youngest owl-faced monkey was afraid to leave the tunnel, for example, so we helped by putting in a few additional climbing structures at the place where he tends to stop. If that leads to positive changes in his behaviour, we will know we did the right thing!'

Indispensable link

Through this project, the welfare researchers are bringing various teams at the zoo together. ‘Our students and our research staff share their data with other researchers working at the Antwerp Zoo Centre for Research and Conservation (CRC). In consultation with the curators for the various species and the animal care coordinators, recommendations drawn from the data are shared by all parties concerned, including the zookeepers, who contribute information from their own observations in turn’, explains curator Sarah. But that’s not all: if they see anything that could be improved in the enclosure, they can call on the technical service department or landscaping for assistance. And when it’s finally time to genuinely introduce the owl-faced monkeys to the gorillas, they will inform the press office.

'The information contributed by these animal welfare researchers has a significant international impact!' - curator Sarah Lafaut

The information collected by these welfare researchers has a significant international impact. ‘Thanks to this vast amount of data, we can offer advice and even assistance to other zoos. Breeding programmes for gorillas, such as the European Endangered Species Programmes (EEP), are extremely interested in this information. We are happy to share our expertise, whether that concerns the behaviour of our owl-faced monkeys and gorillas, co-housing or the introduction between the two species – which will be taking place soon. Our research continues, as we will be conducting new behavioural studies to see how the primates interact with one another once they are truly cohabiting. We are also continuously engaged in observing other species’ behaviour with a view to measuring, improving and safeguarding their wellbeing. In short: To be continued!’