The drawing below was based on a photograph - Terry an infant, had apparently been killed by her genetic father. Here her corpse is surrounded by her mother and siblings. Two weeks later her mother had disappeared. Due to the events leading up to this, I guessed the father had killed the mother as well.
Terry's father - Mr Alfie - had moved into this troop a year earlier. It is normal for relationships to become turbulent when a new male moves into a troop and new males generally act more aggressively than long term male residents who are more secure in their relationships with other members.
From the start Mr Alfie had a severely turbulent relationship with Teleka, the top ranking female and mother of Terry. Prior to his move into the troop, the troop had been led by Kaya, an alpha male who had died after being electrocuted on a pylon. Like Kaya, Mr Alfie was the sole adult male in this troop of eleven individuals. He had no male competitors to challenge the aggression he brought to the troop.
Although I do not know the reason why this troop had only one adult male, the small size of the troop and the skew in adult males to females appears to have contributed towards fatalities.
Many troops in South Africa are showing a skew in adult male to female ratios due to the males being targeted by humans. 
After witnessing a number of infanticide - or juvenile attacks which may be related - amongst wild troops of vervet monkeys and chacma baboons, and having once had the unfortunate experience of watching two baby orphan baboons I was fostering killed during an infanticide attack, I have arrived at the conclusion that attacks on infants and juveniles are often motivated by re-directed aggression.
While infanticide committed by new males moving into a troop may be motivated by the need to ensure lactating females come into oestrus more quickly, I suspect this is merely one reason behind the instances of infanticide that occur.
The few baboon infanticide cases I have witnessed have occurred under different and varied circumstances. A number of fatally injured juvenile and infant monkeys have been brought to me with head wounds or severe spinal injuries, clearly caused by adult male monkeys; considering the extent of these injuries, I have assumed that the motivation was to kill. Biting the victim in the middle of the spine ensures paralysis of the lower body, immobilizing the victim. Adult male monkeys sometimes practice this same kind of attack on adult male opponents.
Taking all the cases I have seen into consideration, I have concluded that both chacma baboons and vervet monkeys commit infanticide or attack juveniles to:
1. Bring lactating females into oestrus: this hypothesis is only relevant in the infanticide cases as killing juveniles who are already weaned would be implausible.
2. To fatally wound a helpless young individual that is assumed to be genetically close to one’s adult opponent (re-directed aggression). This occurs during territorial disputes and when new adult males move into a troop.
3. The behaviour of chacma baboons and vervet monkeys in captivity is vastly altered and higher incidences of violence are more likely between adults (of both sexes); infanticide and juvenile attacks would therefore also be more possible as individuals are unable to escape.
Young primates are used as weapons during conflict situations between adult males. Young juveniles who have lost their mother (due to being shot, electrocuted, run over etc), and have too few adult allies, are likely to be prime targets for infanticidal males.
When rehabilitating a troop of vervet monkeys or chacma baboons, the risks of infanticide and fatal attacks on juveniles, need to be taken into consideration. All individuals need to be strongly bonded, with each member having enough adult allies to protect them under risky conflict situations. Sex and age ratios need to be as appropriate as possible. The troop needs to be large as small troops are at great risk of not surviving.
While infanticide committed by new males moving into a troop may be motivated by the need to ensure lactating females come into oestrus more quickly, I suspect this is merely one reason behind the instances of infanticide that occur.
The few baboon infanticide cases I have witnessed have occurred under different and varied circumstances. A number of fatally injured juvenile and infant monkeys have been brought to me with head wounds or severe spinal injuries, clearly caused by adult male monkeys; considering the extent of these injuries, I have assumed that the motivation was to kill. Biting the victim in the middle of the spine ensures paralysis of the lower body, immobilizing the victim. Adult male monkeys sometimes practice this same kind of attack on adult male opponents.
Taking all the cases I have seen into consideration, I have concluded that both chacma baboons and vervet monkeys commit infanticide or attack juveniles to:
1. Bring lactating females into oestrus: this hypothesis is only relevant in the infanticide cases as killing juveniles who are already weaned would be implausible.
2. To fatally wound a helpless young individual that is assumed to be genetically close to one’s adult opponent (re-directed aggression). This occurs during territorial disputes and when new adult males move into a troop.
3. The behaviour of chacma baboons and vervet monkeys in captivity is vastly altered and higher incidences of violence are more likely between adults (of both sexes); infanticide and juvenile attacks would therefore also be more possible as individuals are unable to escape.
Young primates are used as weapons during conflict situations between adult males. Young juveniles who have lost their mother (due to being shot, electrocuted, run over etc), and have too few adult allies, are likely to be prime targets for infanticidal males.
When rehabilitating a troop of vervet monkeys or chacma baboons, the risks of infanticide and fatal attacks on juveniles, need to be taken into consideration. All individuals need to be strongly bonded, with each member having enough adult allies to protect them under risky conflict situations. Sex and age ratios need to be as appropriate as possible. The troop needs to be large as small troops are at great risk of not surviving.
