A case of infanticide in a recently found gelada population in Arsi, Ethiopia

There have been no reports of infanticide in wild gelada baboons and it has been argued that infanticide is not necessary in geladas, since the birth interval of female gelada can be shortened after takeover of a unit by a new leader male without infanticide. However, we observed an instance of infanticide in a newly-found wild gelada population in the Arsi Region of Ethiopia. After a leader male of the unit was severely wounded by a leopard attack, he was quite weakened. The second male of the unit, a young adult male, became the leader of the unit three weeks later, but the former leader continued to stay in the unit as a second male. After a week, two other adult males joined the unit which, therefore, came to include four adult males. The infanticide took place nine days later. The perpetrator was one of the immigrant males and he showed great interest in the mother of the unweaned victim infant. Although the perpetrator copulated with her after the infanticide, the usurper was found to own all three adult females after two weeks following the infanticide; i.e. the perpetrator could not own any female. The wounded former leader showed conspicuous protective behavior towards the victim's mother and the dead infant. One possible explanation for the occurrence of infanticide in this population of geladas is as follows. Gelada males in this area may be able to join units more easily to form multi-male units but then have shorter tenure in the units. Facing the unstable condition of units, they may sometimes engage in infanticide to increase their breeding opportunities, even before becoming a leader.     

An attempted within-group infanticide in wild chimpanzees

Two high-ranking adult male chimpanzees (Pan troglodytes) of M group in the Mahale Mountains National Park, Tanzania, tried to get a newborn female infant of an adult female who was born in M group. The mother was not seen to mate with these adult males during the probable conception cycle of the infant, but she disappeared from the group during the later cycle, when she may have been inseminated by a male of one of the neighboring unit groups. The adult males failed to get the infant because the grandmother of the newborn and her female friend cooperated to protect the mother and infant from attacks by the males. The sexual selection hypothesis for infanticide by adult male chimpanzees holds for this observed case. The sudden disappearance of another infant, a healthy female, strongly suggests the killing of female infants too. Therefore, the asserted male-biased infanticide in chimpanzees appears to be less tenable.     

Observed case of maternal infanticide in a wild group of black-fronted titi monkeys (<Emphasis Type="Italic">Callicebus nigrifrons</Emphasis>)

A maternal infanticide was observed in a group of unprovisioned wild black-fronted titi monkeys (Callicebus nigrifrons). An approximately 3-day-old male infant was killed by his mother. A post-mortem revealed the infant to be clinically healthy. We considered various hypotheses to explain why this behavior occurred (e.g., reproductive advantage, stress, nutritional, infant viability and population density). It is noteworthy that the mother and not the father killed the infant, since in this species the father provides considerable infant care from a few hours after birth.     

Male Infanticide in the Golden Snub-Nosed Monkey (<Emphasis Type="Italic">Rhinopithecus roxellana</Emphasis>), a Seasonally Breeding Primate

In nonhuman primates, infanticide by adult males can occur when the leader male is ousted from a one-male, multifemale group, or when male dominance rank changes within a multimale, multifemale group. According to the sexual selection hypothesis, this behavior may be adaptive if perpetrators increase their reproductive success by killing unrelated, unweaned infants, thus shortening the interbirth interval of the mother, and then siring her next infant. Under an alternative hypothesis, infanticide is a byproduct of aggressive male–male competition and these predictions do not hold. Direct observations of the context surrounding infanticide in free-ranging primate populations that allow a test of these predictions are rare. Here, we document four cases of male infanticide and report paternity data for a group of golden snub-nosed monkeys (Rhinopithecus roxellana) at Shennongjia, China. Three cases of infanticide by new leader males supported the predictions of the sexual selection hypothesis, while another provides partial support for the sexual selection hypothesis, but can also be explained via a nonadaptive hypothesis. In this latter case, a male from an all-male group killed an infant during an aggressive episode that appeared to be accidental, as it took place 7 mo before a male takeover happened, and the perpetrator did not obtain any reproductive advantage. We conclude that most male infanticide events in golden snub-nosed monkeys are consistent with the adaptive selection sexual hypothesis.     

Infanticide in <Emphasis Type="Italic">Cercopithecus mitis stuhlmanni</Emphasis> in the Kakamega Forest,Kenya: Variation in the Occurrence of an Adaptive Behavior

Infanticide by males is widespread across mammals and especially prevalent among primates. Considerable research has examined how fitness benefits can explain the occurrence of this behavior; less is known, however, about intrapopulation variation in its occurrence. We evaluated 10 infanticides by males in wild blue monkeys according to the sexual selection hypothesis. To explore intrapopulation variation in occurrence of infanticide, we compared these cases to 38 cases that were contextually similar but in which infanticide did not occur. We examined male reproductive benefit, infant age, maternal parity, postconception estrus, group defense, available mating partners, and context of takeover. We based comparisons on daily or near daily records of male presence in the study groups, infant birth dates, and male-female sexual interactions. Infanticides followed predictions of the sexual selection hypothesis: males were unlikely to kill their own offspring, the period for the mother’s return to conception was reduced by half, and males increased their chance of siring her next offspring. Difference in male reproductive benefit, costs, and motivation did not fully explain the observed variation in infanticide occurrence. Infants were more likely to be spared if they were older when a male first arrived, or if their mother had mated with the male in the second month after conception. The most important determinant of infant fate, however, was male identity, a finding consistent with 2 scenarios: 1) an infanticidal tendency may be influenced by a genetic polymorphism that is not fixed in this population or 2) infanticidal behavior may be a conditional male strategy. Further research on intrapopulation variation in infanticidal behavior should focus especially on characteristics of males.     

Within-group cannibalism by adult male chimpanzees

In the Mahale Mountains National Park, Tanzania, a young adult male chimpanzee was observed to feed on a 3-month-old male infant of the same unit-group. Four other adult males and an adult female shared the carcass. The mother of the victim had immigrated from a neighboring unit-group four years previously. Circumstantial evidence strongly suggests that the first-observed cannibal male also killed the infant. The adult male and the mother of the victim had been familiar socially and sexually with each other since the female immigrated. Since the mother of the victim had usually been ranging in the peripheral part of the unit-group's range, i.e., the overlapping area of the two unit-group's ranges during pregnancy and soon after birth, the infanticidal male might have had reason to suspect the paternity of her infant. Four such cases of within-group cannibalism by adult males suggest that the female range and association pattern before and after parturition are key factors allowing an infant to survive. The possibility of male-biased infanticide is also discussed.     

Infanticide in Propithecus diadema edwardsi: An Evaluation of the Sexual Selection Hypothesis

Infanticide might be described as a reproductive strategy employed by anthropoid primate males when they immigrate into new groups. But infanticide has rarely been observed in wild prosimian primates. For the Malagasy lemurs this may reflect one or more of the following: strict breeding seasons; relative monomorphism in canine tooth and body size; small group sizes; male–female dominance relations; and male–female dyads within groups. We addressed the following questions: Do prosimian males commit infanticide in circumstances similar to those in which anthropoids do? and Is there any reproductive advantage for a highly seasonal breeder to commit infanticide? To help answer these questions, we describe the death of a 24-hr-old infant male Propithecus diadema edwardsi from wounds received during a fight between his mother, her adult daughter, and a newly immigrant male. Interbirth intervals between surviving offspring are 2 years for Propithecus diadema edwardsi; therefore, a male could dramatically shorten the time between reproductive windows by killing an infant. Whether this tactic would be favored by sexual selection cannot be addressed until more information has been collected on the length of interbirth interval due to infanticide relative to that of infant death by other causes; how social factors such as stability of breeding relationships affect long-term male reproductive success; how effective female counterstrategies are to prevent infanticide and/or whether they choose to mate with males that commit infanticide; and how often males that kill infants subsequently sire infants, particularly in groups that contain a resident male.     

Infanticide risk and infant defence in multi-male free-ranging sooty mangabeys, Cercocebus atys

For years, infanticide by males was thought to be unlikely in multi-male primate species. Recent studies have, however, presented evidence of infanticide in such species and a recent model by Broom and colleagues predicts that males’ age and rank influence the occurrence of infanticide: youngest and highest-ranking immigrant males are more likely to commit infanticide than their older and lower-ranking counterparts if putative fathers fail to protect infants. I collected data on adult free-ranging sooty mangabey females in the Taï National Park, Ivory Coast, over 11 months including a birth and a mating season. Infanticide had been previously reported in captivity for this species, but not in the wild. Several males entered the group prior to and during the mating season. As predicted by the model, only the more dominant immigrant ones attacked mother-infant pairs significantly more often than did other males. Mothers often reacted with counter-attacks. Potential fathers guarded and supported infants and mothers throughout the period of infant vulnerability. Furthermore, as only one of seven infants died despite 136 observed attacks on mother-infant pairs and unattended infants by immigrant males, we conclude that cooperation between putative fathers and mothers represents an effective protection against infanticide.     

Adult male replacement and subsequent infant care by male and siblings in socially monogamous owl monkeys (<Emphasis Type="Italic">Aotus azarai</Emphasis>)

Owl monkeys (Aotus azarai) are small, territorial, socially monogamous primates that show intense infant care by the adult male in the group. It has been hypothesized that male care may be adaptive because it increases offspring survival and/or reduces the metabolic costs to the female of raising the offspring. Alternatively, males may provide care even when they are not related to the infants to increase future reproductive opportunities. We describe changes in infant care patterns that took place after the eviction of the resident male by a solitary male in an owl monkey population in the Argentinean Chaco. The resident male and mother provided all infant care during the first month of life of the infant, until the male was evicted. During the three-day male replacement event, care of the infant was shared among the mother, a four-year-old sister, and a one-year-old brother. The new male began contributing to infant care soon after entering the group, carrying, and interacting socially with the infant in much the same way as any male regularly does. However, despite receiving biparental care from both the original and new resident males, the infant disappeared at the age of four months and was presumed dead. These are the first reports of care by sibling and by non-putative fathers in wild owl monkeys. Given the significant amount of time that new pairs of owl monkeys spend before reproducing, it is possible that male care in owl monkeys functions as mating effort as much as or more than parenting effort.     

Infanticide following male takeover event in Verreaux’s sifaka (<Emphasis Type="Italic">Propithecus verreauxi verreauxi</Emphasis>)

Two infanticides occurred after a male takeover in a population of Verreaux’s sifaka (Propithecus verreauxi verreauxi) at Beza Mahafaly Special Reserve, Madagascar. The first infant was found dying from wounds received to the chest and groin after three adult males had immigrated into the group. The second infanticide was directly observed 2 weeks later when one of the immigrant males targeted and attacked the infant after it was separated from its mother. The directed nature of the attack suggests that the infant’s death was not a result of generalized aggression during a period of increased group instability. Although the sexual selection argument does not fully explain infanticidal events in seasonally breeding lemurs, such as Verreaux’s sifaka, it is clear that transferring males present a measurable threat to infant survival and female reproductive success in this species.     

A fatal attack on an unweaned infant by a non-resident male in a free-ranging group of Japanese macaques (Macaca fuscata) at Katsuyama

A non-resident male attacked a 4-month-old unweaned infant in a free-ranging group of Japanese macaques (Macaca fuscata) and it died 2 days later from a severe wound. When the infant was alone at the feeding site, the non-resident male rushed at it. The infant ran away as soon as it became aware of the male, but was captured. The male bit the infant on its hand, foot, and arm, while continuously scanning his surroundings. He did not kill the infant immediately and, after the infant escaped, he did not chase or attack it at all. Although the infants right arm was bleeding heavily, it survived until the following day. The infanticide occurred a few weeks before the mating season began, so the victims mother soon resumed estrus and the subsequent inter-birth interval was shortened. The first-, second-, and fourth-ranking adult males had died or disappeared a few months before this infanticide, and there were no other group members near the infant when the infanticidal male appeared. The infanticidal male had not been observed before this incident. Compared to one-male groups, the occurrence of infanticide in multi-male groups of Japanese macaques is extremely infrequent. However, in other reports of infanticide in Japanese macaques as well as in this case, it has been noted that infanticide is likely to occur in the pre- or early-mating season, when there are no resident males to defend the infant against attacks, and when a threatening male is least likely to be the infants father.Electronic Supplementary Material Supplementary material is available for this article at     

Infanticide in a group of wild saddle-back tamarins, Saguinus fuscicollis

An infanticide was observed in a group of wild saddle-back tamarins, Saguinus fuscicollis. The newborn singleton was killed by its mother after it had fallen from the carrier several times. This infanticide may represent a case of parental manipulation: the mother terminated investment in an offspring that probably had a low chance of survival. Also, stress associated with the simultaneous pregnancy of another adult female in the group may have played a role.     

A case study of mother-son transfer in mountain gorillas

In mountain gorillas (Gorilla g. beringei), male immigration in bi-sexual units is rare. This paper presents the case of a nearly weaned male infant gorilla who followed his mother in her transfer. This case was recorded in the study population at the Kariske Research Center in 1988. The data come from observation in Group B (on 12 days just prior to the transfer and on 54 days after the transfer over a period of 6 months). The situation of the infant did match the conditions in which infanticide occurs in gorillas, but he was not killed, despite receiving male aggression and being wounded twice. In fact, both the mother and the infant received male aggression more frequently than the long term residents in the group. The aggression received by the mother decreased after she mated with the males and after she weaned the infant. The aggression received by the infant, however, did not decrease after his mother mated with the males, and increased in intensity. The infant reacted fearfully to male aggression, in marked contrast to his mother, who reacted either with indifference, or by simply avoiding the males. The aggression eventually stopped, and the infant became a blackback in Group B. Evolutionarily, the death of the infant would not have markedly accelerated the mother's return to estrus, but the death of the infant could still have benefitted the males, by decreasing the reproductive output of a competitor. Adult male gorillas are also presumably selected to resist male immigration. Proximately, the aggression directed towards the infant was not related to mating access to the mother. The sex of the infant may contribute to explain the post-transfer male aggression, but data on the integration of old female infants in a new group is needed to test whether the sex of the infant has an effect on their vulnerability to infanticide. Also, the intense fear displayed by the infant may have played a role in prompting male aggression.     

New records of within-group infanticide and cannibalism in wild chimpanzees

Two cases of within-group infanticide and cannibalism were observed among the M Group chimpanzees of the Mahale Mountains, Tanzania. In both cases, victimized infants were male, 5 – 6 months of age, and in good health when killed. Four to five years have passed since the mothers of the victims immigrated into M Group as nulliparous immigrants. In one case the 2nd-ranking male was observed to detach the infant from the mother's belly. Both infants were finally killed by the alpha male after several adult males scrambled for the bodies. There was no evidence that the mothers had mated with males other than those of M Group. Nor was there evidence that the mothers had restrictive mating relationships with some of the M Group adult males. What little evidence is available shows that the mothers had mated mostly with adolescent and other immature males during their conception cycles. However, at least in one case, the mother began to mate more with adult males rather than with immature males after the infanticide. It is proposed that the function of within-group male infanticide can be explained by the male-male competition hypothesis developed for hanuman langurs and other nonhuman primates.     

Infanticide in chimpanzees: Review of cases and a new within-group observation from the Kanyawara study group in Kibale National Park

A prolonged attack on a mother and 2-year-old infant that resulted in the death of the infant was observed in the Kanyawara study group in Kibale National Park. The mother was a border-area resident who was first observed associating with unit-group males six years previously. The attackers were an adult male and an adult female with a 6-week-old infant clinging ventrally to her. The attack was unusual in several respects: it is the first time a male and a female chimpanzee have been observed cooperating closely in an infanticidal attack; the adult female initially attempted to intervene in the victim's behalf, but later joined in the attack after receiving aggression from the male; and the episode was longer in duration than other reported cases. In the year following the incident, the mother did not increase her association with community males, but was seen with the male who killed her infant. The relevance of these observations to sexual selection-based explanations for infanticide in chimpanzees is discussed.     

The variable social organization of hanuman langurs(Presbytis entellus), infanticide,and the monopolization of females

Data from 24 wild populations of hanuman langurs (Presbytis entellus)in south Asia are used to test hypotheses seeking to explain variation in troop structure and the incidence of infanticide. The occurrence of infanticide is associated with a one-male troop structure and not with a high density. The density, predation, and economic-advantage hypotheses, as explanations for the occurrence of one-male and multimale troops, are not supported by the review. However, the monopolization hypothesis is not contradicted; the number of adult males per troop is significantly correlated with troop size and with the number of adult females per troop. Therefore it is suggested that a one-male troop structure will arise if a male is able to monopolize a group of females, a multimale troop if he cannot. One-male troops may predispose to infanticide because of high variance in male mating success and high intermale competition between groups rather than within troops. If female dispersion determines troop structure, it is speculated that females could manipulate males to form a multimale society if the advantages in terms of infant survival and intertroop conflict exceeded the costs in terms of not producing infanticidal “sexy sons.”     

The social behavior of adult male-infant pairs of Rhesus macaques in a laboratory environment

Adult males in nonhuman primate societies exhibit a wide range of behaviors toward immature members of their social group, ranging from virtually continuous nurturance to systematic infanticide. Among macaques, rhesus monkey males in the wild display perhaps the least degree of paternalistic behavior toward conspecific infants. But adult male-infant rhesus attachments have not as yet been explored in a controlled longitudinal study, even though the mother-infant bond has received careful attention for several decades. In the present study two pairs of adult male and infant rhesus macaques were housed together without the mother for a period of at least seven months. To minimize the probability of physical harm to the infants, one adult male was present at the birth of the infant with whom it was paired and the other was visually familiarized with the infant for several weeks before being paired with it. Both pairs have shown much less ventral-ventral contact than mother-infant pairs and the infants have rarely attempted to gain nipple contact. The female infant now initiates and maintains ventral-ventral contact much more frequently than the male infant in spite of the higher degree of aggression directed toward her by the male. The adults frequently groom their infants and exhibit varying degrees of both tolerance and aggression. Rough-and-tumble play appeared quite early in both pairs and is much more vigorous than mother-infant play. Recently the male-male pair has exhibited reciprocal mounting and thrusting. Comparisons are made with data obtained in an earlier study of mother-infant pairs conducted under nearly identical experimental circumstances. The effects of separating the adult males and infants at seven months are also described.     

First occurrence of twins in provisioned free-ranging Tibetan macaques (Macaca thibetana) at Huangshan, China

A first case of newborn Tibetan macaque (Macaca thibetana) twins was observed in a free-ranging group at Huangshan, China. The female that gave birth to the twins was studied during their first 5 months post-partum, and her activity budget was compared to those of adult females with single or no offspring in order to assess her behavioral changes. Our report shows that female Tibetan macaques can produce twins, and that twins can successfully survive. The adult female with twins spent more time foraging and resting, but less time moving and engaged in other social behaviors than adult females with a single infant or no infant. Our report provides a case of successfully surviving twins in a wild environment and suggests that the mother modified her behavior patterns to adapt to the heavy burden. We conclude that both food provisioning and the mother’s behavioral strategies facilitated the survivorship of twins. This expands our understanding of the reproductive biology of Tibetan macaques.     

Evidence for sexually selected infanticide in captiveCercopithecus mitis,Cercocebus torquatus,andMandrillus leucophaeus

Adult resident males of one-male-multi-female primate groups housed at the Hannover Zoo exhibited aggression, when confronted with nonadult individuals, which were fathered by other males: (1) a new adult resident male in a group of blue monkeys killed a 5.8-month-old female infant: (2) a new adult resident male in a group of white collared mangabeys injured a 24.0-month-old female and an 18.9-month-old male severely; they would have died without veterinary care; and (3) the resident male of a group of drills threatened an 1.8-month-old foreign female infant seriously; efforts to introduce the infant were discontinued. Pathological explanations are unlikely because the adult males showed no aggression towards own nonadult offspring under the same captive conditions. By and large, the events support the theory that infanticide is the result of sexual selection among males.     

Are demographic correlates of white-faced capuchin monkey (Cebus capucinus) “Gargle and Twargle” vocalization rates consistent with the infanticide risk assessment hypothesis?

Zahavi's “Bond Testing Hypothesis” states that irritating stimuli are used to elicit honest information from social partners regarding their attitudes towards the relationship. Two elements of the Cebus capucinus vocal repertoire, the “gargle” and “twargle,” have been hypothesized to serve such a bond-testing function. The greatest threat to C. capucinus infant survival, and to adult female reproductive success, is infanticide perpetrated by alpha males. Thus, we predicted that infants (<8 months), pregnant females and females with infants would gargle/twargle at higher rates than the rest of the population, directing these vocalizations primarily to the alpha male. Over 16 years, researchers collected data via focal follows in 11 habituated groups of wild capuchins in Lomas Barbudal, Costa Rica. We found some support for our hypothesis. Infants and females with infants (<8 months) vocalized at higher rates than the rest of the population. Pregnant females did not vocalize at relatively high rates. Infants (age 8–23 months) were the only target group that vocalized more when the alpha male was not their father. Monkeys gargled and twargled most frequently towards the alpha male, who is both the perpetrator of infanticide and the most effective protector against potentially infanticidal males.