“New Evidence on the Tool-Assisted Hunting Exhibited by Chimpanzees (Pan troglodytes verus) in a Savannah Habitat at Fongoli, Sénégal”: Critical Review
Introduction
The chimpanzee population of Fongoli, Sénégal are the only known non-human primate population to systematically (rather than opportunistically) use tool-assisted hunting techniques to capture vertebrate prey. This study examines the tool-assisted hunting patterns of these chimpanzees by both age and sex classes to test the hypothesis that the hunting patterns of Fongoli chimpanzees differ from other chimpanzee populations. Tool-assisted hunting allows for chimpanzees to obtain prey, who would otherwise be unlikely to do so. This study suggests that the frequency of females engaging in tool-assisted hunting at Fongoli can be explained by the social tolerance among the Fongoli chimpanzees, with prey theft being far less frequent than it is in other chimpanzee populations. The tool-assisted hunting patterns of the Fongoli chimpanzees give insight into the importance of the tool-assisted hunting of early hominins, suggesting that they would have had to enhance the tools that they used to hunt in order to overcome environmental pressures. This study is especially relevant to gaining insight into the hunting patterns of early hominins, as the savannah environment of Fongoli is ecologically similar to the environment they would have lived in.
DISCUSSION
Methodology, Research, and Discussion
The number of Chimpanzees in the Fongoli population ranged from 29-36 over the course of the study, averaging at about 31.7 chimpanzees annually. Some females were only semi-habituated when systematic behavioural observation commenced. Adult males were the focal subjects of the study and adult female hunting behaviour was only analysed in mixed-sex hunting groups. The age-classes studied were defined as: infants (less than 4 years), juveniles (4-7 years), adolescents (7-15 years males or females before giving birth) and adults (males 15+ years or females after giving birth). Hunting was classified as: capture (when a hunt was observed), capture out of sight (when a hunt was not observed but possession occurred after an observed chase or when tool-assisted hunting was heard), and possession (when no hunt was observed, but chimpanzee had a prey’s carcass in its possession). The tool-assisted hunting methods that chimpanzees use in order to capture vertebrate prey, such as Galago prey, is considered hunting, as the prey is mobile, hostile, and chimpanzees show an aversion to being attacked by them. In most analyses, infant and juvenile data was combined, as no successful hunt was ever recorded for this age group, and their skill level was deemed insufficient for hunting.
Over the course of the study, a total of 99 hunting cases were observed, including both tool-assisted and non-tool assisted hunting. There were 41 hunts classified as capture, 50 as possession, and 8 as captured immediately out of sight. Female chimpanzees accounted for 30% of the hunts and made up 40% of all successful hunters. Galago prey accounted for over half of all vertebrate species the chimpanzees hunted, and tool-assisted Galago capture made up 21% of all hunts. Adult males captured 52% of all Galago prey obtained, however Galago made up a larger proportion of the prey profile of female chimpanzees than males (75% compared to 47%). 308 tool-assisted captures were recorded, making an annual average of 30.8 hunts per year over the course of 10 years. About 95% of tool-assisted hunts occurred during the wet or transitional season. Although males accounted for 61% of the group composition on days when tool-assisted hunting was observed, only 39% of tool-assisted hunts were executed by males. Out of the 44 potential chimpanzee hunters, 35 were observed to hunt with tools over the course of the study. The median number of tool-assisted hunts per individual was 11, with females averaging at 10.6 hunts each, and males at 6.8. The overall tool-assisted hunting success rate at Fongoli was 7.5%, with the overall probability of successful tool-assisted hunting increasing with age. Adult male chimpanzees were the second least-likely of the age-sex class groups to partake in tool-assisted hunting, yet had higher rates of success in this area. This pattern is surprising, as males tend to be the primary hunters among other chimpanzee populations. Galago prey make up most of the prey caught by females, but less than half of the prey caught by males. The low tool-assisted hunting rates of Galago prey in male chimpanzees can be explained by the low effort return it yields, as Galago are relatively small in comparison to the other prey that can be caught by Fongoli chimpanzees. Male hunting of Galago prey can be seen as opportunistic rather than targeted, as they tend to prey on Galago that have already been drawn out of sleeping cavities through the use of tools by other chimpanzees. Fongoli chimpanzees exploit prey typically ignored by chimpanzees at other sites, as the preferred prey of chimpanzees, the red colobus monkey, is not found in the savannah environment. The social tolerance among the Fongoli chimpanzees is surprising, with prey theft occurring less than 5% of the time, compared to 25% of the time at other sites. Therefore, it is more advantageous for females at Fongoli to hunt than at other sites, as the probability of their prey being stolen by a more dominant individual is relatively low. Tool-assisted hunting at Fongoli enables chimpanzees who would otherwise be far less likely to obtain prey to hunt. The information obtained through this study supports the hypothesis that early hominins enhanced the tools they used to hunt in an effort to overcome environmental pressures. It is likely that early hominins engaged in tool-assisted hunting behaviour, as shown through the data obtained at Fongoli.
Discussion of Positive Aspects
I found this article to be extremely interesting. The research they presented was unique, and they showed this by stating that the chimpanzees at Fongoli are the only known non-human primate population to systematically engage in tool-assisted hunting to capture vertebrate prey. I thought that the specification of systematic tool use was especially important, as there are other chimpanzee populations that have been observed to hunt using tools, such as at the Mahale site, where two instances of tool-assisted hunting occurred (Nakamura and Itoh 2008, 3). The authors went beyond simply making this specification, and actually acknowledged the study at Mahale, where tool-assisted hunting was observed. They explained that the rarity of tool-assisted hunting at this site makes this behaviour opportunistic rather than systematic. I thought that the specification of vertebrate prey was also important, given that chimpanzees have been observed to deliberately fashion sophisticated brush-tipped termite fishing probes using herb stems in the Goualougo Triangle, in Congo (Sanz, Call, and Morgan 2009, 294-295). Termite fishing is incredibly similar to the tool-assisted hunting of Galago prey, as both require drawing out prey from cavities, using tools (Hunt 2015). However, the authors prove that the tool-assisted hunting of Galago prey is indeed hunting, by stating that the prey is mobile, can be aggressive, and chimpanzees express aversion to being bitten. Although a lot of the methodology was beyond my level of understanding, aside from the highly complex statistical methods used, I found it relatively easy to understand. I found it extremely helpful that they defined terms such as what is a “successful hunt”. This made it much easier to understand how they obtained their data. They clearly defined the age-sex classes they used to categorize chimpanzees, and the categories of observed hunting. In general, I found this article relatively easy to understand.
Discussion of Negative Aspects
The authors of this paper stated that the environment that the earliest hominins would have lived in is ecologically similar to that of the Fongoli chimpanzees. I thought this was incredibly interesting, however, they did not elaborate on this point whatsoever, making it a rather vague statement. The source they provided does not mention any similarities between the two environments at all, making it confusing where they drew these similarities from (White et al. 2009, 75-86). They provided no comparison of the two environments and did not list the ways that the environments are similar, making these ecological similarities they spoke of very difficult for the reader to see if they are not familiar with both the environments of early hominins, and the Fongoli chimpanzees. The authors described Fongoli as a savannah environment with a “mosaic of woodland, grassland, bamboo and gallery forest habitats” (pg 2). I found this description rather vague, and had a hard time comparing it with the environment described in the source they provided. The authors of this study noted that when systematic behaviour observation began, many female chimpanzees were not fully habituated, expressing distress and agitation around observers when male chimpanzees were not present. The hunting behaviour of adult female chimpanzees was only analyzed when they were in mixed-sex hunting groups, in an effort to prevent the poaching for their infants in the pet trade. Habituation is essential for accurate observations to be made. The behaviour of unhabituated primates differs greatly from habituated primates, as shown in a seven-month study from 2014-2015 of the behavioural changes in moor macaques (Macaca maura) during the habituation process. The macaques in this study went from ignoring the observers less than 20% of the time at the beginning of the habituation process, to ignoring the observers more than 80% of the time towards the end (Hanson and Riley 2017, 10). Given this drastic change in behaviour exhibited by the macaques, I find it highly unlikely that the female chimpanzees would not show any signs of nervousness around the observers when in mixed-sex groups. This would evidently influence their hunting data. Furthermore, it is possible that the hunting behaviour of female chimpanzees would differ in all-female hunting groups. The concerns of habituating the female chimpanzees are valid, however the researchers could have explored other alternatives to physically observing them, such as camera traps, which have been used for behavioural observation in other studies (Pebsworth and LaFleur 2014, 828-829). I felt that some of the conclusions drawn about early hominin behaviour were very unclear and did not have enough information to support them. The authors mentioned that their data supports the hypothesis that environmental pressures caused early hominins to enhance their tool-assisted hunting technology. Although they cited sources they used, I would have liked them to have been more direct, describing which environmental pressures early hominins would have experienced, and how that related to the tool-assisted hunting patterns at Fongoli. Overall, the lack of elaboration of vague points and the failure to completely habituate female chimpanzees makes it rather difficult for me to completely trust the results of this study. The authors must include more evidence on the environment of early hominins and the environmental pressures that they would have experienced and specifically state it in their article, making direct comparisons to the data that they collected in their research, rather than tacking a citation onto the end of a vague statement. In addition, further research on female hunting patterns in all-female groups at Fongoli is required, using either fully habituated chimpanzees, or alternative observation methods.
Conclusion
The purpose of the research presented in this article is to examine the systematic tool-assisted hunting patterns of the Fongoli chimpanzees that are used to catch vertebrate prey. It seeks to highlight environmental and social factors unique to the Fongoli population of chimpanzees that help to explain their systematic tool-assisted hunting patterns and the frequency at which females engage in tool-assisted hunting behaviours. This article links the data obtained at Fongoli with the importance of tools in early hominin hunting behaviour, suggesting that hominins enhanced the development of their hunting tools in response to environmental pressures.
Females accounted for approximately 30% of all hunts observed and made up 40% of all successful hunters. There was an average of 30.8 tool-assisted hunts annually, with 95% of them occurring in either the wet or transitional season. Males were responsible for only 39% of tool-assisted hunts, despite making up 61% of the group composition on days when tool-assisted hunting was observed. The median number of tool-assisted hunts was higher in females than males, with females averaging at 10.6 hunts and males at 6.8 hunts. The overall tool-assisted hunting success rate at Fongoli was 7.5%, and the probability of a successful tool-assisted hunt tended to increase with age. Adult male chimpanzees were less likely compared to other age-sex classes to engage in tool-assisted hunting, however had higher rates of success. Galago prey are hunted far more frequently by females than males, likely due to the low energy return that they yield compared to other prey. Males often capture Galago prey after they have already been drawn out of their sleeping cavities by others, making their hunting of this particular type of prey opportunistic rather than targeted. The hunting patterns unique to Fongoli can be explained by the absence of their preferred vertebrate prey, the red colobus monkey, leading them to take advantage of prey that other chimpanzee populations ignore. Prey theft at Fongoli occurs less than 5% of the time, compared to 25% of the time at other sites, making it more advantageous for less dominant chimpanzees (such as females) to hunt, as there is a low probability that their prey would be stolen by a more dominant chimpanzee. This data shows that early hominins likely enhanced the tools they used to hunt in an effort to overcome environmental pressures, and that tool-assisted hunting was very important to them.
The data obtained through this study shows that chimpanzee hunting is less male-biased than previously thought, and that females play a significant role in hunting, accounting for the majority of the tool-assisted hunting exhibited by the Fongoli chimpanzees. The research here supports the hypothesis that hominins may have used tool-assisted hunting to overcome environmental pressures, such as did the Fongoli chimpanzees, with the red colobus monkey being absent in their environment. It also suggests that females may have had a greater role in hunting than previously believed. The ability of the Fongoli chimpanzees to systematically use tools to hunt shows that even the earliest hominins were likely sophisticated enough to craft tools to aid their hunting. With further development of these ideas and more research, this article could give us a much deeper understanding of how our ancestors hunted.