A new man of the house: can it succeed?

19 Jul 2019 | Back to News, Publications and Annual Reports

BPRC reveals results of fifteen-year study

The best time to introduce new breeding males into a group of rhesus macaques is when the males are at the peak of their strength. Such introductions have the greatest chance of success in groups with many females, from a maximum of three different families. These are only two of the conclusions from a fifteen-year study conducted by behavioural experts at BPRC.

Primates are extremely social creatures. It is vital to their well-being that they be allowed to live with other members of their species and to engage in natural social behaviour. This is why all animals at BPRC are housed in social groups. In the breeding colony, they live in large social groups that mirror those in the wild as closely as possible. Like in the wild, the female macaques at BPRC always remain with the group into which they are born, while the males are removed from their birth groups at puberty. This type of housing practice is unique among research institutions.

A new breeding male

Every breeding group includes one adult breeding male. This breeding male is moved to a new group every four to five years to prevent him from mating with his own female offspring. In the wild, adult males switch groups every few years as well. While necessary, the act of introducing a new breeding male is not without risk. A new breeding male can be aggressive and may injure females and their offspring. For this reason, the females are often less than pleased to have a new ‘man of the house’. They will attempt to discourage him from joining the group. As a result, the introduction of a new breeding male can lead to aggression, stress and injuries to both male and female animals. Sometimes a male proves unable to join a breeding group at all, despite the fact that he is much larger and stronger than the females.

Research into introductions

For the well-being of the animals, it is important to keep the number of introductions to a minimum and to ensure these transitions go peacefully. The male must also be able to maintain his position in the group over the long term, so that he will not need to be switched out earlier than scheduled. To that end, behavioural researchers at BPRC have conducted research to identify the factors that determine whether an introduction will succeed and whether the male will be able to secure a stable position within the group. In doing so, they examined the timing of the introductions, along with the characteristics of both the individual males and the groups.

The researchers studied a total of 64 introductions that took place between 2003 and 2018; 77% of these introductions were successful. Of the successfully introduced males, some 77% managed to maintain their position within the group in the long term. It turned out that the best time for us to introduce males was at an age where they would also change groups in the wild: when their physical strength is at its peak. Males that remain with their birth group until puberty – as they would in the wild – have the best chance of maintaining their (new) position for the long haul. It is best to introduce the males into groups with a large number of females, from no more than three different families, similar to the groups that exist in the wild. Finally, it is important that we avoid placing new males in groups with pregnant females. Wild males also switch groups in a period when there are no pregnant females – shortly before mating season starts.

The more natural, the better

These results emphasise that replicating life in the wild is better for the animals. The more natural the groups and the introductions of new males, the more successful the introductions and the more stable the groups will be. The findings also show that the unique way in which the primates in BPRC's breeding colony are housed improves the animals’ well-being.

The complete scientific article is available here.