More light, more nature

01 Mar 2019 | Back to News, Publications and Annual Reports

Report on the new marmoset enclosures

‘Hi girl, do you want to take a look? How nice.’ Animal care worker Marit is standing in front of a renewed outdoor enclosure for the smallest primates at the BPRC site: the common marmosets, known for their striking white ear tufts. ‘We usually call them marmo’s.’

Suddenly, a brief chorus of whistles rings out from other cages. ‘A crow just flew over,’ says Marit, who is also the Enrichment Coordinator at BPRC. ‘The whistling is how they warn each other.’

A few years ago new, modern enclosures were constructed on this site for all primate species at BPRC, thanks to a major investment by the Ministry of Education, Culture and Science. This has resulted in all primates used for breeding purposes currently being housed in spacious and social living environments. ‘However, there is always potential for making things better and more pleasant,’ says Marit, pointing to what is now a full glass facade. ‘The thick crossbars have been completely removed, allowing in much more natural light. They really love it, and it benefits their vitamin D levels as well.’

When the sun shines

The breeding marmosets have been housed at BPRC since 2003. They are distributed over 34 enclosures, half of which have now been completely rebuilt and the other half of which are nearing completion. Each enclosure houses one breeding group, which always consists of one family: father and mother – ‘marmosets are highly monogamous!’ – and their offspring, often twins. There are usually four to eight animals in total, with a maximum of ten. The marmoset enclosures are half indoors and half outdoors; both sections are and will remain about three metres deep, two metres wide and three metres high. ‘The higher the better, because they are naturally used to living high up in trees.’

In this way, the animals can always choose for themselves whether they want to be indoors or outdoors. ‘When it’s as cold as it is today, they prefer to remain inside, where it’s pleasantly warm and humid. That’s why not everything outside has been completed, as you can see, because we want to have all the indoor elements completed first. But you can see them staring behind the glass, do you see?’ Marin points to one of the little primates. ‘They do actually go outside in winter, certainly when the sun is shining. They are so curious that they can’t resist popping out to size up the situation, like now.’ She nods at a marmoset that has climbed up a branch from the passageway. ‘Hello dad, coming for a quick look?’

Always room for improvement

Thanks to focused training sessions, the animal care workers are now able to handle the animals with greater confidence. This helps when weighing marmosets and, for instance, taking a closer look to see how they are doing. ‘You can use a net or a fabric sleeve to catch the primates, but it’s much more efficient to train them so that they come to you by themselves. So that’s what we teach them, first of all by letting them take a reward out of our hands. That works really well, but we felt there was still room for improvement. One very impractical aspect, for instance, was that they had to travel an unnatural route to get to us, so we had to address this during the renovation work. There are quite a few things that we have altered to facilitate training.’

Marit explains the need to weigh the marmosets: ‘The animals only weigh around 350 grams, so you can’t tell just by looking at them whether one of them has lost or gained 35 grams. However, this is still 10% of their body weight, so it’s incredibly important to be able to monitor this. This applies particularly to pregnant females. Sometimes you don’t know that they’re pregnant until they suddenly give birth. That’s very awkward, of course, so that’s another reason why we started weighing training. The inconvenient thing was that we always had to keep open the front door to the enclosure.’

Marmosets are naturally very territorial and don’t normally wander, unless there is conflict or unrest in the group. ‘Just like in nature. There, the older animals leave their birth group when they reach sexual maturity. This is why we would prefer to have closed cages, which would allow the marmosets to stay on their own turf.’

More natural behaviour

Marit shows a ‘before and after’ video, for which she provides her own commentary. ‘The new enclosure gives us the option of shifting several boxes from the front side of the cage, so we no longer have to open the entire door. I can now move a slider upward and insert a box at four locations in the same cage. That is the signal for the animals that there’s a tasty treat in store. It’s much easier for me to put them on the trolley and onto the scales, without them jumping off again. Now you can observe and note down everything without stress. What’s very nice for the marmosets themselves is that they can get used to the idea of going into a box, with little doors that open and close. If their first encounter with this is in the lab, the process can acquire a negative association, because many more things are happening to the animals in that setting.’

This new approach gives the marmosets a head start with regard to future actions, especially in the sense of reducing stress. ‘We used the renovation as an opportunity to change the layout of the enclosures.’ Marit walks past the enclosures and stops by a space that has now been fully equipped outside as well. It’s full of natural materials. She points out the plants, bushes, bamboo and figs. ‘The animals love it. You see them moving between these plants, hunting for flies. That wasn’t possible before, because the flies didn’t really have anything to land on. There was a tree trunk there, but after a while all the bark had been gnawed off, so it wasn’t much use. And that fig tree doesn’t have any leaves now because it’s winter, but normally it has lovely big leaves. The marmosets love figs – they like to eat them straight out of the tree.’

Besides this, Marit and her colleagues went in search of all kinds of different materials, because they felt that wood alone wasn’t enough. ‘The structure of wood and the feeling of walking over it are very natural, but you want to offer more. That’s why we have those nice, thick ropes and those fun hammocks. Marmosets like to curl up against each other when they sleep, so we’ve made it possible for them to do so. Ultimately, we’ve created a very natural whole, which is nonetheless uncluttered enough for us to retain a good view of all the animals. This achievement is mostly down to my colleague Marlies. By the way, there’s a whole bamboo field further back to provide replacement plants, because they chew them bare in no time at all.’

Light and open

To conclude, Marit walks round to the back of the building to provide a glimpse of the indoor world through the windows of the rear door. As today’s reporter hasn’t undergone a Mantoux test (for tuberculosis), entry is strictly forbidden. Even from this point, however, you can get a good view of the interior, which is very light and open. A cleaner is thoroughly scrubbing the shining floor of the hall between the enclosures, which are set up symmetrically opposite each other. The floors of the enclosures themselves are covered with a carpet of sawdust, in which the marmosets can forage for little blocks of gum and other foods that the animal care workers have ‘hidden’.

One other striking element is the blue cards on the doors, with names such as Fabian, Floris, Fenna and Francisca to the left. ‘All the animals, including the rhesus and long-tailed macaques, are given an animal number and a name,’ explains Marit. ‘The principle for the marmosets is that the names of offspring all start with the same letter as the names of their parents. That way, we always know who belongs to whom. This is also useful for recognising certain character traits – because just as with people, the apple doesn’t fall far from the tree!’