Why Apenheul's new gorilla leader must be introduced to the group slowly

13 Apr 2018 | Back to News, Publications and Annual Reports

Breaking news from Apenheul Primate Park last week: A new gorilla leader has arrived at the zoo. As part of an international breeding programme for gorillas kept in captivity, 33-year-old Bao Bao will be introduced to the zoo's female gorillas over the next few weeks. You see, male gorillas cannot be introduced to females without thorough preparation. But why is that?

In other words, Bao Bao is being gradually introduced by Apenheul. Which, as we know all too well at BPRC, is the only way to do it. While we do not accommodate any apes, such as gorillas or chimpanzees, we know that even with the monkeys in our colony (rhesus macaques, crab-eating macaques and marmosets), new males must be introduced into a group very carefully.

Not all primate species are similar

‘The main reason why new males must be introduced gradually is because they can kill the group's young,’ explains animal care worker Marlies, who is quick to emphasise that not all primate species act the same way. ‘It's vital that you don't lump all primate species together. The various species are simply too different from each other for that, in terms of their social organisation, how they interact, and what requirements they have vis-à-vis each other. Therefore, how to carefully introduce a new primate to a colony is completely dependent on the species and its environment. What is true for gorillas may not be true for macaques, but the risk of infanticide (i.e., males killing the group's young) is an overlapping theme.’

Making females fertile sooner

The risk of infanticide causes female primates to become very protective of their young, just like lionesses grow very protective of theirs. ‘For this reason, males cannot be introduced to a new group just like that,’ says Marlies. ‘They have to be introduced very gradually. As for why a male would kill pre-existing young, well, because the female gets fertile sooner after losing her young, meaning the male can get his own offspring and spread his genes more quickly. In other words, infanticide is a very effective means of procreation, but the females do take precautions of their own – they tend to become very aggressive. Macaque females may bite a male to death. I'm not sure what gorilla females may be capable of.’

Fooling the male

New males should also be weary of pregnant females, as these are are good at fooling males. They may mate with him ad nauseam and treat him to endless grooming rituals, thus making him believe that the young which will be born is his. ‘Guarding the safety of their unborn young is the main reason why these females act that way. Females without young may be more genuinely interested in a new male, but this very much depends on how their sisters and cousins respond to him. If they act very aggressively towards him, the young females will follow the herd and act aggressively to him, too.’

Gradual approach

In other words, a gradual introduction of the new male is the way to go. But what does ‘gradual’ mean in this context? What are the main areas of concern with regard to introducing a male to a new group? Says Marlies, ‘It is important to look at the interactions between the male and the females. Their body language, their gestures. If they are friendly to each other, you can move on to the next step fairly quickly. For instance, you can put the animals together for a few moment, instead of keeping a fence between them. But if they behave aggressively towards each other, leave the fence in place. Wait until they start flirting with each other a little, and be sure to give them plenty of time. Time to get used to each other, and to see where they stand in relation to each other. And be sure to take into account that all monkeys have personalities of their own – just like humans.’

How to win a female's heart

Obviously, the male's response to the female is an excellent indicator in this introduction procedure. ‘In order to win a female's favour, a male primate can basically use two strategies,’ Marlies explains. ‘Either he can be very kind and modest, to the point of aloofness, or alternatively, he can try to rule the roost with an iron fist right from the get-go. Some females respond better to the former strategy, others to the latter. Both of these strategies must have been successful in the past, or else they would no longer exist. But really, each time a strategy has to be chosen is like a first time. Just like we're seeing at Apenheul at present!’