Male crested macaques respond to the screams of infants during conflict

In a recent study published in the International Journal of Primatology, scientists have revealed that male crested macaques (Macaca nigra) are more likely to respond to the screams of their own offspring during combative conflicts. 

The research was led by behavioral ecologist Professor Anja Widdig from Leipzig University and the Max Planck Institute for Evolutionary Anthropology, as part of the Macaca Nigra Project (MNP).

The study was conducted over a period of 24 months, from 2008 to 2010, in the Tangkoko Nature Reserve on Sulawesi, Indonesia. The research is featured in a special issue of the journal dedicated to crested macaques, marking the 17th anniversary of the MNP.

Focus of the study

Primate infants are known to be dependent on help for survival, especially during their first year. While mothers bear the main burden of parental care, the survival of offspring is essential for males as well, for the transmission of their genes. This led the researchers to question how males respond when infants scream for help during conflicts. 

“Many primate species live in groups of several males and females. Promiscuous mating raises the question of whether males can even recognize their genetic offspring. The aim of this behavioral study was therefore to investigate how males respond when infants scream for help,” explained Professor Widdig.

How the research was conducted 

The team observed conflicts involving infant crested macaques, who often scream to solicit support. During over 3,600 hours of observation across three study groups, more than 2,600 infant screams for help were registered and analyzed in relation to the responses of male crested macaques.

What the researchers discovered 

Interestingly, the researchers found that males were more inclined to respond to an infant’s screams if they were the father, a friend of the infant, or a friend of the mother. 

Additionally, high dominance rank males, or those likely to have sired many of the infants themselves, were more likely to react to screaming offspring, as were infants and mothers of low dominance rank, who are particularly dependent on help. 

Notably, the presence of the mother at the conflict site did not influence the males’ response to the infants’ screams.

Investing support

The results suggest that male crested macaques might possess some cues to gauge which infants they have fathered. However, they generally seem to intervene infrequently and even help unrelated infants. 

For example, the data showed that infants screaming for help were mainly involved in conflicts with adult males or females from their social group (42 and 46% respectively), suggesting that males might assess the risk of intervention to avoid potential conflicts with rivals.

“Although previous studies on this primate species have found that fathers do not specifically establish social relationships with their offspring, this study shows that fathers do invest in supporting their offspring, albeit in a very limited way.” 

Parental care is limited

This confirms findings from other studies that males form social bonds with or tolerate their young at feeding sites, but rarely actively support them in conflict situations. 

The researchers believe that any form of paternal care in crested macaques is subtle and limited to certain situations, potentially evolving due to high infant mortality rates.

The reasons for this paternal restraint are multifaceted. It could be that crested macaque offspring do not benefit from spatial associations and social bonds with their fathers, so neither invest in such relationships daily. 

Defending their alpha status

Another explanation could be the lack of time; fathers might be unable to spend much time with their offspring as they can only defend their alpha status for an average of twelve months. 

This leads males to invest their time in mating with as many fertile females as possible before migrating to another group. 

“It is still unclear whether the support of young macaques by unrelated males is actually an active male strategy or a misjudgement of paternity by the male,” said Professor Widdig.

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