In spring 2005 GaiaPark Kerkrade Zoo (the Netherlands) opened its doors to the public. We started with two species of capuchin – the white-throated (Cebus capucinus) and the yellow-breasted (Cebus xanthosternos).The white-throated group consisted of 3.3 animals who were living in the ‘real’ capuchin enclosure, where they shared the outside island area with the capybaras. In the collection plan there was only one species of capuchin, but at this point it was easy to create space for a second species. The group of yellow-breasted capuchins consisted of 1.1 animals who were kept in a smaller enclosure. Both species bred quite well, so in 2007 we decided to give up one of them in order to have room to house one big group of capuchins.

From white to yellow

Because of the fact that it is an EEP species and one of the most endangered primates in the wild, we chose to keep the yellow-breasted capuchins. Moreover, we could get two more females, which would give us the opportunity to build up a nice social group of this species. We were also influenced by the fact that the interactions between the white-throated capuchins and the capybaras were not always very friendly – we even had to keep the new-born capybaras inside for a couple of weeks, because we were afraid that the oldest capuchin male would attack them. The character of the yellow-breasted capuchin seems to be calmer. We found a place for the white-throated group in Wroclaw (Poland). As by now their numbers had grown to 11 animals, they made a very attractive social group to transfer to a new zoo.


In January 2008 we received two female yellow-breasted capuchins. One (Chewbacca) came from Apenheul Primate Park and one (Itapi) from Frankfurt Zoo. They would be introduced to the GaiaPark group, which by that time consisted of 3.1 animals. The breeding male (Eric) came from Colchester Zoo and the female (Choice, full sister of Chewbacca) came from Apenheul. At GaiaPark, Choice had given birth three times. The first infant was stillborn, and the second was a male called Amarillo. The third time Choice had twins, but one of them, a female, died shortly afterwards; the male, Yermo, survived.

When the new females arrived, we put them together in a separate cage within the capuchin enclosure. They accepted each other straight away. The same day we put in Eric without any trouble, and after that we introduced the rest that same day without any negative signs. It was funny, of course, to introduce two full sisters (Choice and Chewbacca); they had lived together at Apenheul and as far as we – people – could tell they recognized each other.

When we fetched Itapi from Frankfurt, however, we saw quite unusual and insecure behaviour. But since she had been separated to be transported, we thought this was the reason for her behaving like that. Shortly after her introduction to the others at GaiaPark, however, Itapi again showed very insecure and almost stereotypic behaviour. We thought it was because of the very strong bonding between Choice and Chewbacca – they sometimes really behaved as only sisters can do!

Of course, we gave things time to settle down: working with animals, we all know that things like this sometimes take a very long time. During the following months, however, there was not a single moment when we were convinced that Itapi was really part of the group. All the time she was the most submissive animal. This was not really a problem – after all, one animal has to take this position. But every day, when the animals had to go inside, we had to force Itapi to do so. On the other hand, we did not see disproportionate aggression towards her. We were used to some aggression with our group of white-throated capuchins, who also had a very clear hierarchy. Moreover, we were still not convinced that Itapi was really afraid of the group or of one of its members. We keepers thought it was sometimes more her own behaviour which gave her this subordinate position.

During these months the other two females came into heat and became pregnant. In August 2008 Chewbacca gave birth. Unfortunately the baby was killed, probably by one of the other group members. Since this is not uncommon in capuchins, we saw no reason for extra stress. A few weeks later, Choice gave birth, again to a son (Mojito). This baby did survive, and after a while we also saw Chewbacca carrying him.

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Yellow-breasted capuchins at GaiaPark.


Summer passed by and, as temperatures dropped, the animals had to spend more time inside. This had a bad influence on Itapi – she lost a lot of weight, got some bald spots, became very stressed and showed stereotypic behaviour. Of course, it took some months for her to reach this stage. During that time, Chewbacca also became very thin and more stressed. We did not know exactly what was best to do, but decided to separate the two females for at least the coldest months of the year and then try to reintroduce them when the weather was better, so that they could spend more time outside again.

Because the capuchin enclosure is quite big and well developed and includes five separate cages, we decided to separate the two females in the same building but in one of the other cages. After two weeks it was clear that this would not work. There was still a lot of stereotypic behaviour (the type which cannot be influenced by enrichment) and stress. So we moved the two females to an enclosure behind the scenes. This enclosure has an inside area and an equal-sized outside area where the animals can see birds and other keepers. It took approximately ten days for them to calm down and start to enjoy life again. Of course we did our best to enrich them and feed them to get on more weight. Luckily this worked out well, and at the end of the winter we had two good-looking capuchin females again.

Boys, boys, boys

Something else that influenced our group was the fact that Choice had given birth only to sons. Our goal was to build up a nice social group. This was still possible with more males – in the wild this species sometimes lives in groups with more than one male. But if we had to separate those males from the group when they became sexually mature, we would lose social enrichment again. With other species, like white-throated capuchins and squirrel monkeys, we had some experience of keeping more males in the groups by castrating them (after discussing it with the EEP coordinator, of course). If we were to do the same with the yellow-breasted capuchins, we would be castrating one of the most threatened primate species in the world. . . On the other hand, there are almost twice as many males as females within the EEP, which isn’t a workable situation either. So after consulting the EEP coordinator, we were allowed to castrate Choice’s three sons. We observed them before and after the castration, but luckily it seems not to have influenced their behaviour at all.


Of course the situation with the two separated females could not continue for ever. In the spring, we started introducing them again. Since we had decided to keep all the males, Choice’s position in the group is very strong (but, to be honest, she already had the best position because she is Eric’s favourite). We thought the problem would not be the actual introduction (since this happened quite easily the first time), but the way of managing the group afterwards. One idea was to give the animals more room: we thought this might reduce the stress factor for the two females. As mentioned before, our inside enclosure is especially suitable for complex groups: the animals can use several escape routes and five different enclosures. Normally we keep the capuchins inside for the night, but now we decided to let them choose to go outside as well, to give them more space and freedom.

We made a good plan for the introduction – to build it up gradually. But – as always when you plan something with animals – things worked out differently. When we put the females back in the capuchin building, all the animals started to greet each other and there was not a single aggressive action or negative sound. We dropped our plan and just opened all the sliding doors. The sisters Choice and Chewbacca were happy to see each other again and Itapi had most attention from the ‘boys’. Even when they were all together, there was no aggression. They all knew each other and life seemed to be the same as before the separation.

Besides giving the capuchins more space and freedom, we also changed our working methods with them. In the morning they were all locked inside for breakfast. If necessary we separated Itapi and Chewbacca to give them some extra food (a high-protein ‘ball’ which we also give to the gorillas). In the mean time we spread the rest of the food on the island or put it in the feeding baskets which were hanging in the trees. After some 15 minutes, they were allowed to go outside again. We tried to repeat this routine four times every day, which mostly worked out very well (90% of the time they come voluntarily); if not, we tried to spread the food on the island by throwing it over the water moat or fed them inside in all the cages. Three of the five inside enclosures were not visible to the public, so in the past these parts had been shut off during opening hours. But now, when we gave them all the space, we found that though some of them spent time out of sight, there were always some on view to the public. (We had a student observing who confirmed this.)

To summarize: in 24 hours, if the weather was good enough, the animals spent ten hours locked outside on the island (except for the feeding times during the day), and for the other 14 hours they could choose to be inside or outside. Capuchins are tough monkeys and can spend a lot of days locked outside. Since we fed them at least four times a day, a keeper could observe the group behaviour every two and a half hours, which gave us quite a good picture of what was going on.

Calming down

This way of managing the capuchins led to a very calm and stable group. Itapi was still the one who would be picked on in moments of stress, but every social group needs an underdog like that. At the end of the summer we were even expecting three youngsters! Chewbacca and Itapi gave birth first. Although the deliveries went well, the babies were unfortunately killed a few days later. The third to give birth was Choice, and her youngster (another male – Kesi Kesi) survived. (Both the dead infants were also males.) Of course it was very sad that their youngsters died, but the position of Chewbacca and Itapi in the group was better, and that was important. But with winter coming up, we had a new problem. . .

Winter again

Normally in the Netherlands winters are mild, but at times during the last two years the water moat around the capuchin island had been filled with ice. Since we didn’t want to separate the two females again and it was no option to keep the animals inside all winter (because of the stress), we needed a solution to keep the moat from freezing. Our technicians came up with a simple but strong pump, the sort of thing normally used to oxygenate pond water, and by using this we managed to keep the water open.

At the beginning of the winter, we were afraid that Itapi might stay outside on the island all night, while it was freezing cold. To ease our anxiety, we went to the zoo late in the evening and early in the morning, but luckily all the monkeys were sleeping inside. During the day we separated them a bit more than in the summer, so that they had more chance to eat and relax, and things worked out really well.

Table 1. The GaiaPark yellow-breasted capuchin group.

Males Females
Name Place of birth Date of birth Name Place of birth Date of birth
Eric Colchester 09/08/1999 Choice Apenheul 09/03/2000
Amarillo* GaiaPark 08/07/2006 Chewbacca Apenheul 09/09/2002
Yermo* GaiaPark 03/09/2007 Itapi Frankfurt 01/10/2002
Mojito* GaiaPark 05/09/2008
Kesi Kesi GaiaPark 07/09/2009
* neutered

An end to breeding

Itapi’s position in the group is still rather a mystery to us, but at least she is functioning there right now, which is of course most important for such a social primate species. What would be good for her in our opinion is having a youngster. Unfortunately, though, we had to stop breeding with our yellow-breasted capuchins on the request of the EEP coordinator. We did not immediately know how we would solve this problem, but eventually decided to give a hormone implant not to the females but to the breeding male. In September 2009 we gave Eric Deslorin for the first time; this product lasts for six months and seems to work well. The females have a normal oestrus but so far have not become pregnant again. In February 2010 we gave Eric Deslorin again; we did not take out the first one because then there might have been a chance of his becoming fertile for a short period. (So if we need to treat him a third time, we will take out the first implant and leave the second one in, and so on.)If there comes a time when we are allowed to breed again, we have to find out how to manage the group in such a way that we can protect the youngsters from being killed – maybe to separate them for ten to 14 days, or to separate the males and the females. We are not sure, because at present we still don’t know why they were killed, or which animal(s) did it. But we have solved other problems before, so there will no doubt be a solution for this one too.For now, at any rate, we have quite a nice group of 5.3 animals (see Table 1, above) who are living happily together. And for the moment, that’s the most important thing!

Tjerk ter Meulen, GaiaPark, Dentgenbachweg 105, 6468 PG Kerkrade, the Netherlands (