Reciprocity and beyond: Explaining meat transfers in savanna-dwelling chimpanzees at Fongoli, Senegal.

OBJECTIVES: To understand the function of food sharing among our early hominin ancestors, we can turn to our nonhuman primate relatives for insight. Here, we examined the function of meat sharing by Fongoli chimpanzees, a community of western chimpanzees (Pan troglodytes verus) in southeastern Sénégal. MATERIALS AND METHODS: We tested three non-mutually exclusive hypotheses that have been used to explain patterns of food sharing: kin selection, generalized reciprocity, and meat-for-mating opportunities. We analyzed meat sharing events (n = 484) resulting from hunts, along with data on copulations, age-sex class, and kinship to determine which variables predict the likelihood of meat sharing during this study period (2006-2019). RESULTS: We found full or partial support for kin selection, direct reciprocity, and meat-for-mating-opportunities. However, the analyses reveal that reciprocity and a mother/offspring relationship were the strongest predictors of whether or not an individual shared meat. CONCLUSIONS: The results of this study emphasize the complexity of chimpanzee meat sharing behaviors, especially at a site where social tolerance offers increased opportunities for meat sharing by individuals other than dominant males. These findings can be placed in a referential model to inform hypotheses about the sensitivity of food sharing to environmental pressures, such as resource scarcity in savanna landscapes.

Wild Chimpanzee Welfare: A Focus on Nutrition, Foraging and Health to Inform Great Ape Welfare in the Wild and in Captivity.

Adequate nutrition is essential for individual well-being, survival and reproductive fitness. Yet, in wild animals, including great apes, scoring nutrition or health comes with many challenges. Here, we have two aims: first, broadly review the scientific literature regarding nutritional data on wild chimpanzee foods to get a better understanding what nutrients foods comprise of, and second, highlight important findings on wild chimpanzee nutrition and welfare pertaining to diet. We discuss variation in macro and micronutrients in food items consumed and their role in chimpanzee health across chimpanzee subspecies from multiple study sites. We found a lack of information pertaining to nutritional consumption rates of daily diets. Second, we call for a fresh, in-depth discussion on wild chimpanzee welfare issues is of foremost importance to inform conservation projects and particularly settings where humans and chimpanzees may interact, because such conversation can reveal how specific or general welfare measures can (a) inform our knowledge of an individual's, group's, and population's welfare, (b) provide additional measures from the study of wild chimpanzee ecology that can guide the welfare of captive chimpanzees, and (c) can enable comparative study of welfare across wild populations. A summary of the current literature on approaches to measuring wild chimpanzee health and welfare status, to our knowledge, has yet to be done.

Investigating foundations for hominin fire exploitation: Savanna-dwelling chimpanzees (Pan troglodytes verus) in fire-altered landscapes.

Humans' extensive use of fire is one behavior that sets us apart from all other animals. However, our ancestors' reliance on controlled forms of fire-i.e., for cooking-was likely preceded by a long familiarity with fire beginning with passive exploitation of naturally burned landscapes and followed by intermediate steps including active ecological modification via intentional burning. Here we explore our pyrophilic beginnings using observational data from savanna-dwelling chimpanzees. These data highlight the extent to which anthropogenic burning impacts the behavior and ecology of sympatric primates and provides an opportunity to study the ways in which apes living in a fire-altered world exploit opportunities presented by burning. Using monthly burn scar data and daily range use data we quantify the impact of burning episodes on chimpanzee habitat. Over the course of one dry season, approximately 74% of the total estimated range of the Fongoli community of savanna-dwelling chimpanzees (Pan troglodytes verus) was impacted by fire. We combine fire occurrences with behavioral data to test for relationships between burning and rate of encounter with food items and duration of subsequent patch residence time. Results show more frequent encounters and shorter patch residence times in burned areas. These data can be leveraged as a frame of reference for conceptualizing our extinct relatives' behavior around fire.

Chimpanzees (Pan troglodytes) in savanna landscapes.

Chimpanzees (Pan troglodytes) are the only great apes that inhabit hot, dry, and open savannas. We review the environmental pressures of savannas on chimpanzees, such as food and water scarcity, and the evidence for chimpanzees' behavioral responses to these landscapes. In our analysis, savannas were generally associated with low chimpanzee population densities and large home ranges. In addition, thermoregulatory behaviors that likely reduce hyperthermia risk, such as cave use, were frequently observed in the hottest and driest savanna landscapes. We hypothesize that such responses are evidence of a "savanna landscape effect" in chimpanzees and offer pathways for future research to understand its evolutionary processes and mechanisms. We conclude by discussing the significance of research on savanna chimpanzees to modeling the evolution of early hominin traits and informing conservation programs for these endangered apes.

Western chimpanzees (Pan troglodytes verus) access a nutritionally balanced, high energy, and abundant food, baobab (Adansonia digitata) fruit, with extractive foraging and reingestion.

Intrinsic to several hypotheses explaining the evolution of foraging behavior complexity, such as proto-tool use, is the assumption that more complex ingestive behaviors are adaptations allowing individuals to access difficult to procure but nutritionally or energetically rewarding foods. However, nutritional approaches to understanding this complexity have been underutilized. The goal of this study was to evaluate potential nutritional determinants of two unusual foraging behaviors, fruit cracking with anvils and seed reingestion, by adult male western chimpanzees (Pan troglodytes verus) at Fongoli, Senegal during the baobab (Adansonia digitata) fruit season. We examined these behaviors in relation to nutrient and energy intake, and compared macronutrient and energy concentrations found in baobab fruits to other plant foods. Adult males ingested at least 31 distinct foods from 23 plant species. Baobab fruit comprised the majority of daily energy intake (68 ± 34%, range: 0%-98%). The energetic concentration of baobab fruit varied by phenophase and part ingested, with ripe and semi-ripe fruit ranking high in energy return rate. Males preferred ripe and semi-ripe baobab fruit but unripe fruit intake was higher overall. The seed kernels were high in protein and fat relative to fruit pulp, and these kernels were easier to access during the unripe stage. During the ripe stage, seed kernels were accessible by reingestion, after the seed coat was softened during gut passage. In addition to providing macronutrients and energy, baobab fruit was a relatively abundant food source. We conclude that baobab pulp and seed are high quality foods at Fongoli during the baobab season because they are nutritionally balanced, high in energy, and relatively abundant in the environment. These nutritional and abundance characteristics may explain, in part, why these chimpanzees use anvils and reingestion to access a mechanically challenging food.

Informing Protection Efforts for Critically Endangered Chimpanzees (Pan troglodytes verus) and Sympatric Mammals amidst Rapid Growth of Extractive Industries in Senegal.

Updated information on Critically Endangered western chimpanzees (Pan troglodytes verus) in Senegal is urgently needed, given that gold mining is rapidly transforming landscapes and livelihoods. Specifically, biodiversity assessments will better elucidate the chimpanzee extinction risk here and yield baselines for monitoring. We compared mammal species richness between Fongoli (unprotected) and Assirik in Niokolo-Koba National Park to assess the efficacy of the only nationally protected area where chimpanzees range in this country. The primary habitat difference between these sites was the degree of human activity. Although Assirik and Fongoli had similar mammal assemblages and were equivalent in primate species richness, the protected area was higher in species richness overall, particularly for ungulates and carnivores. The protected status and management plan of Niokolo-Koba almost certainly resulted in fewer mammal extinctions. In unprotected areas, the flexible behavioural responses of chimpanzees to human-driven landscape dynamics is likely essential to their long-term survival. Furthermore, the near absence of chimpanzee killings in this country greatly facilitates conservation efforts. Given that mineral extraction is a key development strategy in Senegal, we encourage primatologists to collaborate with mining stakeholders to ensure that sustainability programming includes contributions from experts in savannah chimpanzee behavior and ecology.

Stable isotope variation in savanna chimpanzees (Pan troglodytes verus) indicate avoidance of energetic challenges through dietary compensation at the limits of the range.

OBJECTIVES: Food scarcity is proposed to be a limitation to chimpanzees at the limits of their range; however, such a constraint has never been investigated in this context. We investigated patterns of δ13 C and δ15 N variation along a latitudinal gradient at the northwestern West African chimpanzee (Pan troglodytes verus) range limit with the expectation that isotope ratios of chimpanzees at the range limit will indicate different dietary strategies or higher physiological constraints than chimpanzees further from the edge. MATERIALS AND METHODS: We measured δ13 C and δ15 N values in hair (n = 81) and plant food (n = 342) samples from five chimpanzee communities located along a latitudinal gradient in Southeastern Senegal. RESULTS: We found clear grouping patterns in hair δ13 C and δ15 N in the four southern sites compared to the northernmost site. Environmental baseline samples collected from these sites revealed overall higher plant δ15 N values at the northernmost site, but similar δ13 C values across sites. By accounting for environmental baseline, Δ13 C and Δ15 N values were clustered for all five sites relative to total Pan variation, but indicated a 13 C-enriched diet at the range limit. DISCUSSION: Clustering in Δ13 C and Δ15 N values supports that strategic shifting between preferred and fallback foods is a likely ubiquitous but necessary strategy employed by these chimpanzees to cope with their environment, potentially allowing chimpanzees at their limits to avoid periods of starvation. These results also underline the necessity of accounting for local isotopic baseline differences during inter-site comparison.

Nest-Building Behaviour by Chimpanzees (Pan troglodytes verus) in the Non-Protected Area of Diaguiri (Kedougou, Senegal): Implications for Conservation.

Diaguiri is a non-protected area situated in south-eastern Senegal. Chimpanzees (Pan troglodytes verus) have been living here since 1999 but information on the characteristics of their nest sites have been lacking until now. Furthermore, we implemented nest survey methods recently standardised to arid landscapes during a national chimpanzee survey. Variations in nest decay rates are poorly understood in savanna-woodland mosaic habitats. This study aims to describe in Diaguiri: (1) the distribution of chimpanzee nests and the location of their core sleeping area, (2) the tree species used for nest building, (3) the association between nests and nesting tree heights, and (4) differences in nest decay rates between habitats. We surveyed 43 km of chimpanzee nesting habitats and recorded 871 nests in gallery forest and woodland habitats between March 2015 and June 2016. Diaguiri chimpanzees used at least 17 tree species for nest building, and 58.8% of nests were in only 3 tree species: Pterocarpus erinaceus, Anogeissus leiocarpus and Diospyros mespiliformis. Nest decay rate was faster in gallery forests than in woodlands. These data are of great value for understanding habitat use by a Critically Endangered subspecies of savanna chimpanzee, for population density estimates of the species and for conservation programmes in this region and in savanna biomes.

Savanna chimpanzees adjust sleeping nest architecture in response to local weather conditions.

OBJECTIVES: Great ape nests are hypothesized to aid safe, secure sleep via providing thermoregulation or protection from predators and vectors. We aimed to describe and investigate variation in chimpanzee nest architecture across two populations in response to local weather conditions. MATERIALS AND METHODS: We experimentally tested whether nests provide insulation by measuring heat loss within and outside nests, and took detailed measurements of the number, size, and type of materials used in nest building across two dry-habitat research sites (Fongoli, Senegal, and Issa, Tanzania). We tested application of principal components analysis (PCA) to extract composite quantitative measures of the key components of shape and architecture, before testing how PCs vary across populations with overnight weather conditions that reflect hypothesized thermoregulatory function. RESULTS: Heat loss is greater and occurs faster outside of nests. PCA allowed meaningful comparison of nests within and between sites. Nest variation at both sites revealed chimpanzees built thicker nests in cooler conditions and used more broken branches and support in moister conditions. Chimpanzees in Fongoli used more lining and mattress material in colder conditions, whilst in Issa nest depth and support branch size were larger in windier conditions. DISCUSSION: Shape and architectural measures reflected insulation and stability of nest structure. Chimpanzees in Fongoli and Issa may achieve the same functional goals by adjusting nest shape and architecture in different ways. These results suggest that wild chimpanzees show flexible building techniques in response to local, overnight weather conditions in making an insulating and stable, supportive platform for sleep.

The costs of living at the edge: Seasonal stress in wild savanna-dwelling chimpanzees.

Adaptations associated with shifting from a predominately forested habitat to a more open environment are considered a crucial step in hominin evolution. Understanding how chimpanzees, one of our closest-living relatives, are exposed to the selection pressures associated with living in a relatively sparse, hot, and dry environment can inform us about the relative importance of potential environmental stressors involved in adaptations to drier environments. We investigated the extent to which chimpanzees living in an extreme savanna habitat experience seasonal variability in either energy balance or thermoregulation (dehydration and heat exposure), as well as whether these potential environmental constraints are taxing to chimpanzee individuals. Specifically, we tested the hypothesis that savanna environments impose seasonally-relevant costs to chimpanzees. To this end, we collected 368 urine samples from one community of chimpanzees at Fongoli, Senegal, and measured c-peptide, creatinine, and cortisol as measures of physiological responses to environmental food, water, and heat constraints, respectively. We then evaluated the influence of climatic and phenological factors on these indicators. Results illustrated significant seasonal variation in all biomarkers, which corresponded to relevant ecological correlates. Furthermore, creatinine but not c-peptide correlated with cortisol levels, suggesting that chimpanzees in this environment endure periods of heat and dehydration stress, but are able to avoid stressful levels of negative energy balance. Using savanna chimpanzees as a referential model, our research lends support to the notion that thermoregulatory challenges were a significant factor in hominin evolution, and suggests these challenges may have overshadowed the challenges of maintaining adequate energetic balance during the expansion of the hominin range from wetter to drier environments.

Nocturnal behavior by a diurnal ape, the West African chimpanzee (Pan troglodytes verus), in a savanna environment at Fongoli, Senegal.

OBJECTIVES: I report on the nocturnal behavior of Fongoli chimpanzees in a savanna mosaic during different seasons and lunar phases and test the hypothesis that hot daytime temperatures influence activity at night. I predicted that apes would be more active at night during periods of greater lunar illuminosity given diurnal primates' lack of visual specializations for low-light conditions and in dry season months when water scarcity exacerbated heat stress. MATERIALS AND METHODS: I observed chimpanzees for 403 hrs on 40 nights between 2007 and 2013 and categorized their activity as social, movement, or vocalization. I scored their activity as occurring after moonrise or before moonset and considered the influence of moon phase (fuller versus darker phases) as well as season on chimpanzee nocturnal behavior in the analyses. RESULTS: Results indicate that apes were more active after moonrise or before moonset during fuller moon phases in the dry season but not the wet season. Most night-time activity involved movement (travel or forage), followed by social behavior, and long-distance vocal communication. DISCUSSION: Animals in highly seasonal habitats often exhibit thermoregulatory adaptations but, like other primates, chimpanzees lack physiological mechanisms to combat thermal stress. This study provides evidence that they may exhibit behaviors that allow them to avoid high temperatures in a savanna environment, such as feeding and socializing at night during the hottest time of year and in the brightest moon phases. The results support theories invoking thermal stress as a selective pressure for hominins in open environments where heat would constrain temporal foraging niches, and suggest an adaptability of sleeping patterns in response to external factors.

Feeding in fear? How adult male western chimpanzees (Pan troglodytes verus) adjust to predation and savanna habitat pressures.

OBJECTIVES: We evaluated risk-sensitive foraging in adult male western chimpanzees (Pan troglodytes verus) occupying a savanna environment at Fongoli, Senegal. The aim of this study was to determine how the risks of predation and heat stress influenced their behavior while feeding on a key food, fruit of the baobab tree (Adansonia digitata). MATERIALS AND METHODS: Proximity of fruiting baobab trees to anthropogenic landmarks were compared to food intake, feeding rate, and behavioral indicators of fear in adult males (N = 11) at Fongoli. Additionally, we compared foraging to vegetative habitats, baobab ripe fruit nutritive quality, surface water availability, and foraging party composition. RESULTS: Fruit abundance increased with proximity to anthropogenic landmarks, and chimpanzees exhibited higher frequencies of antipredator behaviors as they approached these risky areas. However, predation risk did not deter adult males from visiting these fruiting trees; instead, risky foraging bouts were associated with higher food intakes and longer feeding times. Additionally, higher feeding rates were observed in open-canopy habitats, and this behavior may have minimized their risk of heat stress. CONCLUSIONS: Adaptations that minimize predation risk are widespread in mammalian prey species, but these traits are poorly understood in chimpanzees. Great apes encounter few nonhuman predators capable of successfully capturing and killing them; thus, such events are rarely observed. Although people rarely hunt chimpanzees in Senegal, we found that adult males perceived humans as predators and adjusted their behavior while foraging in risky habitats. From an applied perspective, risk-taking behavior is important for understanding and mitigating the problem of crop-feeding in locations where chimpanzees and humans live in sympatry.

Chimpanzees (Pan troglodytes verus) and their mammalian sympatriates: Mt. Assirik, Niokolo-Koba National Park, Senegal.

In intact, mosaic ecosystems, chimpanzees are sympatric with a wide range of other mammals, which may be predators, prey, or competitors. We delve beyond the nominal data of species lists to interval-level data on 35 medium-bodied and large-bodied mammals encountered at a hot, dry, and open field site in far West Africa. Frequency of encounter, habitat where found, and number of individuals encountered are analysed for species for which enough data were accumulated. Further, we compare findings over three periods (1976-1979, 2000, 2012). Species most often encountered were those normally classed as typical savanna forms. Even a crude classification into forest, woodland, and grassland ecotypes yields differences in species likely to meet apes. Comparison of encounter rates over time was surprisingly congruent, although not all species seen in the 1970s survived to the 2000s. Overall, Assirik's mammalian fauna is comparable to palaeo-faunal guilds sympatric with various extinct hominins.

Reconstruction of periodicity of repetitive linear enamel hypoplasia from perikymata counts on imbricational enamel among dry-adapted chimpanzees (Pan troglodytes verus) from Fongoli, Senegal.

Periodicity of repetitive linear enamel hypoplasia (rLEH) in apes from high latitudes with single wet and dry seasons annually has not been described. We reconstruct periodicity and duration of rLEH in canine teeth from three recently deceased chimpanzees from Fongoli, Senegal with a marked seven-month dry season. High-resolution dental molds were taken in the field for magnified imaging with digital microscopy. Photomontages allowed counting of perikymata between episodes of rLEH for reconstruction of periodicity and duration of physiological stress. Where rLEH spans the imbricational enamel, the number of events is consistent with years required to form canine imbricational enamel; i.e., periodicity of rLEH seems circannual. We predicted perikymata counts between rLEH events ranging from 52 to 61 based on reported "long counts" of 7-6 days. Counts ranged from 29.5 to 44, individual mean of 36.7. This discrepancy could be explained by recurrent stress with a periodicity of 7.2-8.4 months, or by long counts of 10 days per stria. Neither is supported in the literature. Since we find evidence of rLEH with circannual periodicity, we postulate the existence of non-emergent imbricational striae. Based on evidence that stress at Fongoli recurs annually, we reconstruct stress duration of 2-3 months, longer than reported for chimpanzees living in other habitats, which we attribute to heat stress and food shortage near shrinking waterholes. We conclude that canine teeth from a small mortality cohort of chimpanzees at Fongoli preserve a faithful record of dry season stress in an extreme environment.

Plant-food and tool transfer among savanna chimpanzees at Fongoli, Senegal.

Transferring food is considered a defining characteristic of humans, as such behavior is relatively uncommon in other animal species save for kin-based transfer. Chimpanzees (Pan troglodytes) are one exception, as they commonly transfer meat among nonrelatives but rarely transfer other resources. New observations at Fongoli, Senegal, show habitual transfer of wild-plant foods and other non-meat resources among community members beyond transfers from mother to offspring. We explore various explanations for these behaviors with a focus on age- and sex-class patterns in transfer events. In a total of 27 of 41 cases, male chimpanzees at Fongoli transferred wild-plant foods or tools to females. Most other cases involved transfer among males or males taking food from females. In light of male-female transfer patterns at Fongoli, we examine four hypotheses that have been applied to food transfer in apes: (1) testing for male-coercive tendency (van Noordwijk and van Schaik, Behav Ecol Sociobiol 63:883-890, 2009), (2) costly signaling (Hockings et al. PLoS ONE 2:e886, 2007), (3) food-for-sex (Gomes and Boesch, PLoS ONE 4:5116, 2009), and (4) sharing-under-pressure (Gilby, Anim Behav 71:953-963, 2006). We also consider hypotheses posed to explain transfer among callitrichids, where such behavior is more common (Ruiz-Miranda et al. Am J Primatol 48:305-320, 1999). Finally, we examine variables such as patch and food size and food transport. We discuss our findings relative to general patterns of non-meat transfer in Pan and examine them in the context of chimpanzee sociality in particular. We then contrast chimpanzee species and subspecies in terms of non-meat food and tool transfer and address the possibility that a savanna environment contributes to the unusual pattern observed at Fongoli.

Insectivory of savanna chimpanzees (Pan troglodytes verus) at Fongoli, Senegal.

Little is known about the behavior of chimpanzees living in savanna-woodlands, although they are of particular interest to anthropologists for the insight they can provide regarding the ecological pressures affecting early hominins living in similar habitats. Fongoli, Senegal, is the first site where savanna chimpanzees have been habituated for observational data collection and is the hottest and driest site where such observation of chimpanzees occurs today. Previously, indirect evidence suggested these chimpanzees consumed termites throughout the year, an unusual occurrence for western and eastern chimpanzees. Although meat eating by chimpanzees continues to receive much attention, their use of invertebrate prey has received less emphasis in scenarios of hominin evolution. Here, we further examine the invertebrate diet of Fongoli chimpanzees using direct observational methods and accounting for potential environmental influences. Termite feeding positively correlated with high temperatures. Fongoli chimpanzees spend more time obtaining termites than any other chimpanzee population studied, and this extensive insectivory contributes to the list of distinctive behaviors they display relative to chimpanzees living in more forested habitats. We suggest that savanna chimpanzees at Fongoli differ significantly from chimpanzees elsewhere as a result of the selective pressures characterizing their harsh environment, and this contrast provides an example of a viable referential model for better understanding human evolution. Specifically, our results support the hypotheses that invertebrate prey may have figured more prominently into the diet of early hominins in similar habitats, especially given that invertebrates are an important source of protein and other essential nutrients in a highly seasonal environment.

Orangutans (Pongo spp.) may prefer tools with rigid properties to flimsy tools.

Preference for tools with either rigid or flexible properties was explored in orangutans (Pongo spp.) through an extension of D. J. Povinelli, J. E. Reaux, and L. A. Theall's (2000) flimsy-tool problem. Three captive orangutans were presented with three unfamiliar pairs of tools to solve a novel problem. Although each orangutan has spontaneously used tools in the past, the tools presented in this study were novel to the apes. Each pair of tools contained one tool with rigid properties (functional) and one tool with flimsy properties (nonfunctional). Solving the problem required selection of a rigid tool to retrieve a food reward. The functional tool was selected in nearly all trials. Moreover, two of the orangutans demonstrated this within the first test trials with each of the three tool types. Although further research is required to test this statistically, it suggests either a preexisting preference for rigid tools or comprehension of the relevant features required in a tool to solve the task. The results of this study demonstrate that orangutans can recognize, or learn to recognize, relevant tool properties and can choose an appropriate tool to solve a problem.

Brief communication: Reaction to fire by savanna chimpanzees (Pan troglodytes verus) at Fongoli, Senegal: Conceptualization of "fire behavior" and the case for a chimpanzee model.

The use and control of fire are uniquely human traits thought to have come about fairly late in the evolution of our lineage, and they are hypothesized to correlate with an increase in intellectual complexity. Given the relatively sophisticated cognitive abilities yet small brain size of living apes compared to humans and even early hominins, observations of wild chimpanzees' reactions to naturally occurring fire can help inform hypotheses about the likely responses of early hominins to fire. We use data on the behavior of savanna chimpanzees (Pan troglodytes verus) at Fongoli, Senegal during two encounters with wildfires to illuminate the similarities between great apes and humans regarding their reaction to fire. Chimpanzees' close relatedness to our lineage makes them phylogenetically relevant to the study of hominid evolution, and the open, hot and dry environment at Fongoli, similar to the savanna mosaic thought to characterize much of hominid evolution, makes these apes ecologically important as a living primate model as well. Chimpanzees at Fongoli calmly monitor wildfires and change their behavior in anticipation of the fire's movement. The ability to conceptualize the "behavior" of fire may be a synapomorphic trait characterizing the human-chimpanzee clade. If the cognitive underpinnings of fire conceptualization are a primitive hominid trait, hypotheses concerning the origins of the control and use of fire may need revision. We argue that our findings exemplify the importance of using living chimpanzees as models for better understanding human evolution despite recently published suggestions to the contrary.

Ecological context of savanna chimpanzee (Pan troglodytes verus) termite fishing at Fongoli, Senegal.

Chimpanzees (Pan troglodytes verus) at Fongoli, Senegal, consume termites year-round. Understanding the ecological context behind this behavior is especially important in light of the environmental conditions at Fongoli. This mosaic savanna habitat is one of the hottest and driest sites where chimpanzees have been studied. Two genera and four species of termites were found in association with tools used by chimpanzees in a sample of 124 termite mounds that were monitored. The chimpanzees of Fongoli termite fish predominantly in woodland and forest habitat types, and, although woodland accounts for the majority of the chimpanzees' home range, forest habitat types comprise only about 4% of their range. Thus, habitat type has an influence on the Fongoli chimpanzees' termite fishing. Termite consumption to the degree seen at Fongoli may have particular significance for hominid evolution, given the expansion of Pliocene hominids into increasingly open, hot, and dry habitats.

Do chimpanzees build comfortable nests?

Nests built by wild chimpanzees (Pan troglodytes verus) were studied at the Fongoli research site in southeastern Senegal from January 2004-May 2004 to investigate the role of comfort in nest building behavior by relating measures of nest comfort and building effort. Nest comfort across zones of the nest surface were compared with construction effort for 25 nests. Several variables of nest comfort were assessed: (1) physical discomfort, (2) visible discomfort, and (3) softness. Physical discomfort was used as a representative measure of nest discomfort. Building effort was measured by (1) construction force, (2) complexity, and (3) added material. Spearman rank correlations compared Effort and Comfort measures for both whole nests and central versus edge zones. The results show that construction force and complexity do not influence comfort of the nest as a whole. Greater Construction force correlates with more nest edge discomfort, yet the central area shows no difference. More complex nests do result in a more comfortable central area in the nest. Nests built with greater force may result in more discomfort, whereas complexity may allow chimpanzees to maintain comfort in a central area for sleep. Chimpanzees may place additional leaves or twigs over hard branches, protruding from the nest surface after construction, to increase comfort of the central nest area. Functions of chimpanzee nest building are likely to be several, but these results suggest comfort is a factor in nest building behavior.