We report the first observation of a chimpanzee with albinism in the wild, describe interactions between the infant & other group members, & describe the subsequent infanticide of the individual with albinism by his conspecifics

First observation of a chimpanzee with albinism in the wild: Social interactions and subsequent infanticide. Maël Leroux, Gideon Monday, Bosco Chandia, John W. Akankwasa, Klaus Zuberbühler, Catherine Hobaiter, Catherine Crockford, Simon W. Townsend, Caroline Asiimwe, Pawel Fedurek. American Journal of Primatology, July 16 2021. https://doi.org/10.1002/ajp.23305

Research Highlights

Observations of wild non-human primates with albinism are extremely rare

We report the first observation of a chimpanzee with albinism in the wild

We describe interactions between the infant with albinism and other group members

We describe the subsequent infanticide of the individual with albinism

We discuss these observations in light of our understanding of chimpanzee behavior

Abstract: Albinism—the congenital absence of pigmentation—is a very rare phenomenon in animals due to the significant costs to fitness of this condition. Both humans and non-human individuals with albinism face a number of challenges, such as reduced vision, increased exposure to ultraviolet radiation, or compromised crypticity resulting in an elevated vulnerability to predation. However, while observations of social interactions involving individuals with albinism have been observed in wild non-primate animals, such interactions have not been described in detail in non-human primates (hereafter, primates). Here, we report, to our knowledge, the first sighting of an infant with albinism in wild chimpanzees (Pan troglodytes schweinfurthii), including social interactions between the infant, its mother, and group members. We also describe the subsequent killing of the infant by conspecifics as well as their behavior towards the corpse following the infanticide. Finally, we discuss our observations in relation to our understanding of chimpanzee behavior or attitudes towards individuals with very conspicuous appearances.

4 DISCUSSION

We describe here, to our knowledge, the first observation of a chimpanzee with albinism in a wild ape population. Importantly, we provide a unique account of interactions between the community members and the infant with albinism (and its mother) upon initial encounter and during the day of the infanticide.

The initial reaction of community members towards the infant appeared to be different from a typical situation in which chimpanzees encounter females with a newborn for the first time. Community members of both sexes often show signs of curiosity towards a newborn upon first sighting, such as grooming the mother or looking attentively at the newborn, touching, or grooming it (Goodall, 1986; Gideon Monday and Pawel Fedurek, personal observation). While individuals can respond to such events with excitement or aggression, particularly in the study community where infanticides are common (Lowe et al., 2019), interactions which included apparent fear towards a newborn are unusual and have not been observed to the same extent as seen on this occasion.

Although it is not possible to draw firm conclusions from this one observation, it appears that the encounter with the infant with albinism had an arousing effect on most adult community members. For example, even though some individuals responded calmly to the infant, most adult individuals seemed to react with fear upon encountering the newborn by keeping distance and producing alarm hoos and waa barks. In chimpanzees, these two call types are associated with risky, and potentially deadly situations, such as encountering snakes, bush pigs, or unfamiliar humans (Crockford et al., 2017; Goodall, 1986; Schel et al., 2013). Notably, this initial, apparently fearful, behavior was followed by physical aggression towards the infant and eventually death. In this respect, our observation shares similarities to those recorded in some bird species, where agonistic behaviors towards individuals with albinism were observed (Roberts, 1978).

The captive infant female chimpanzee Pinkie, the only other known chimpanzee with albinism, was captured alive in the wild as a newborn. However, it is not possible to establish how the original community members had reacted to, or interacted with, her before her capture (or whether they had seen her in the first place) as no such records before the capture exist. Similarly, the account of the successful introduction of Pinkie to a group of captive chimpanzees has not been published, which makes it difficult to establish whether and how an introduction of an infant with albinism to a group of stranger chimpanzees differs from an introduction of an in-group chimpanzee infant. We consider, therefore, our descriptive account of interactions of several conspecifics with an individual with albinism from the same wild community as unique.

The Sonso community has a history of infanticide committed by both adult males (Newton-Fisher, 1999) and, more rarely, females (Lowe et al., 2019; Townsend et al., 2007), which includes frequent within-community killings (Lowe et al., 2019). It is, therefore, possible that the infant with albinism would have become a victim of infanticide regardless of its appearance. The way the body was mutilated did not differ considerably from the way bodies of chimpanzee victims of within-community killings are often afflicted (Lowe et al., 2019; Wilson et al., 2014). For example, fingers of the right hand were bitten off, so was (partially) the left foot (see Supporting Information Material 3). However, the magnitude of the reaction some of the community members exhibited towards the infant with albinism makes it likely that the infant was not considered as a typical chimpanzee. The vigilant and even fearful behavior including alarm calling by individuals upon the initial exposure to the infant seems to support this idea.

Similarly, the careful and repeated inspection of the carcass by several individuals ranging from infants to adults of both sexes does not seem to be a typical behavior that chimpanzees direct towards a dead infant. Indeed, in contrast to our observation, most studies report that mainly the mother, and sometimes kin, initiate extended contact with a dead infant, sometimes displaying affiliative behaviors towards it, such as grooming (Biro et al., 2010; Cronin et al., 2011; Lonsdorf et al., 2020). Furthermore, in our study, one adult male was seen using his lips to pinch the hair of the dead infant, and several other individuals were seen stroking the hair of the carcass. Such behaviors have not been reported before in the context of infanticide in the Sonso community (Lowe et al., 2019; Catherine Crockford, personal observation), and could have been elicited by the unusual pigmentation of the infant. Indeed, the behavior of the chimpanzees towards the corpse of the infant with albinism resembles that of chimpanzees when presented with a novel object: Chimpanzees usually engage with such objects with initial caution followed by examining it carefully and touching it (Russell et al., 1997). However, some of the behaviors of group members towards the carcass of the infant with albinism, such as grooming it—a behavior previously described in this context in non-human primates including chimpanzees (Gonçalves & Carvalho, 2019), clearly indicate that the infant was not perceived by them as an object, but as a conspecific of an unusual appearance. However, since observations of chimpanzees interacting with individuals of atypical appearance are very rare, more data of this kind are needed to explore the cognitive mechanisms behind this behavior. Likewise, although our unique observations are potentially relevant to the understanding of chimpanzee death perception (e.g., Gonçalves & Carvalho, 2019), more data of this kind are needed to investigate the cognitive processes underlying it.

The inspection of the carcass by individuals often focused on the anogenital regions, with several individuals inserting their fingers into the anus of the carcass. To our knowledge, only one observation of this kind has been made in chimpanzees before: An adult female inserting a digit in the anus of the former alpha male dead body (Pruetz et al., 2017). In our study, both adult and infant males were seen inserting a digit in the anus of the infant with albinism. Several mammal species possess anal glands that play a role in olfactory communication. For example, anal gland secretion conveys information about kinship in beavers (Castor canadensis) (Sun & Müller-Schwarze, 1998) and lemurs (Lemur catta) (Charpentier et al., 2010). In spotted hyenas (Crocuta crocuta), individuals discriminate identity and social status of a conspecific through anal gland scent (Burgener et al., 2009), whereas black rhinoceros (Diceros bicornis) can differentiate sex and age using gland scent (Linklater et al., 2013). Chimpanzees also use olfactory communication when identifying the recent presence of individuals from other communities in their territory (Henkel & Setchell, 2018). Furthermore, another study on chimpanzees reported an observation of the mother and another adult female bringing their hands towards their face after touching a dead infant as if to gain information about its body (Cronin et al., 2011). Our observation potentially indicates that olfactory cues were used to gain information about the infant with albinism because, for example, it was not perceived by conspecifics as a typical individual or an individual from their own territory.

Although in some species individuals with albinism tend to have smaller body sizes (Slagsvold et al., 1988), the size of the infant in this study was normal considering its estimated 3 weeks of age. Autopsy results did not reveal any apparent major health issues and, during the initial encounter, the infant appeared to behave normally. Thus, we have no observations that suggest that the peculiar behavior of the chimpanzees towards the infant, or its carcass, were driven by any potential morphological abnormalities of the body except its coloration. It is important to note, however, that histopathology tests on the carcass were not conducted, and therefore, we do not have detailed information about the infant's health. The white coloration of the infant bears similarities to that of black and white colobus monkey (Colobus guereza) infants that Budongo chimpanzees often prey on (Reynolds, 2005). Therefore, another intriguing possibility is that the infant's pattern of coloration matched features of this community “prey image” (Uehara, 1997), but with the form and odor of a chimpanzee and this incongruence could explain the behavior of some of the individuals towards the infant.

To conclude, we provide a unique account of behaviors of wild chimpanzees towards an infant with albinism before and following its death. Our observations provide insights into chimpanzee behavior in extremely rare social circumstances.