David Watts

• Doctor of Philosophy
• Professor at Yale University

All great apes build nests. Nests in trees or on the ground provide apes with a safe and comfortable place to sleep and rest at night and during the day. Nest building is a necessary skill and form of tool use that individuals learn and practice early in life, but little is known about its development and about the factors affecting the expression...

Wild chimpanzees (Pan troglodytes) are caught in snares set for other animals and sometimes injure or lose body parts. Snaring can compromise the health, growth, survival, and behavior of chimpanzees and, thus, represents a threat for the conservation of this endangered species. During a long-term study of chimpanzees at Ngogo in Kibale National Pa...

Among mammals, post-reproductive life spans are currently documented only in humans and a few species of toothed whales. Here we show that a post-reproductive life span exists among wild chimpanzees in the Ngogo community of Kibale National Park, Uganda. Post-reproductive representation was 0.195, indicating that a female who reached adulthood coul...

Measuring the relative contributions of milk and non‐milk foods in the diets of primate infants is difficult from observations. Stable carbon (δ ¹³ C) and nitrogen (δ ¹⁵ N) isotopes in hair can be used to physiologically track infant feeding through development, but few wild studies have done so, likely due to the difficulty in collecting hair non‐...

The interaction between infant feeding and maternal lactational physiology influences female inter-birth intervals and mediates maternal reproductive trade-offs. We investigated variation in feeding development in 72 immature wild chimpanzees (Pan troglodytes schweinfurthii) at Ngogo, Kibale National Park, Uganda, and made inferences about maternal...

Many animals engage in aggression, but chimpanzees stand out in terms of fatal attacks against adults of their own species. Most lethal aggression occurs between groups, where coalitions of male chimpanzees occasionally kill members of neighboring communities that are strangers. However, the first observed cases of lethal violence in chimpanzees, w...

Survival in primates is facilitated by commensal gut microbes that ferment otherwise indigestible plant matter, resist colonization by pathogens, and train the developing immune system.¹,² However, humans are unique among primates in that we consume highly digestible foods, wean early, mature slowly, and exhibit high lifelong investments in mainten...

Premasticated food transfer, when an individual partially breaks down food through chewing and feeds it to another individual, usually mouth-to-mouth, is described widely across human cultures. This behavior plays an important role in modern humans’ strategy of complementary feeding, which involves supplementing maternal milk in infant diets with p...

Fruit production in tropical forests varies considerably in space and time, with important implications for frugivorous consumers. Characterizing temporal variation in forest productivity is thus critical for understanding adaptations of tropical forest frugivores, yet long‐term phenology data from the tropics, in particular from African forests, a...

Comparative [“evolutionary”)] thanatology is devoted to investigating how animals respond to signs of death and dying, in conspecifics and other species. Responses to corpses often involve fear and confusion, and “deceased infant carrying” by females is widespread in nonhuman primates. Such behavior could result from “animacy detection malfunctions...

Significance Many animals, especially humans, carry out activities collectively because the benefits of doing so exceed those that can be achieved individually. But how can collective action evolve when individuals receive the benefits of cooperation regardless of whether they pay the costs of participation? Collective action may be especially diff...

Demographic data on wild chimpanzees are crucial for understanding the evolution of chimpanzee and hominin life histories, but most data come from populations affected by disease outbreaks and anthropogenic disturbance. We present survivorship data from a relatively undisturbed and exceptionally large community of eastern chimpanzees (Pan troglodyt...

Alloparenting, when individuals other than the mother assist with infant care, can vary between and within populations and has potential fitness costs and benefits for individuals involved. We investigated the effects of alloparenting on the speed with which infants were weaned, a potential component of maternal fitness because of how it can affect...

The order Primates comprises hundreds of species that vary widely in size, life history, ecology, and behavior. Most diurnal species and some nocturnal ones form stable social groups characterized by permanent association between males and females. Predation has been the main factor selecting for the evolution of group living. Typical group size an...

Although numerous ecological and social factors influence range use in vertebrates, the general assumption is that ranging patterns typically accord with principles of optimal foraging theory. However, given temporal variability in resource abundance, animals can more easily meet nutritional needs at some times than at others. For species in which...

The assumption that population density restricts the foraging efficiency of individuals in the population via increased competition for resources underpins socioecological models of female social relationships in primates. We examined this assumption by comparing quantitative measures of foraging efficiency in two communities of chimpanzees (Pan tr...

Chimpanzees (Pan troglodytes) use some communicative signals flexibly and voluntarily, with use influenced by learning. These signals include some vocalizations and also sounds made using the lips, oral cavity, and/or teeth, but not the vocal tract, such as "attention-getting" sounds directed at humans by captive chimpanzees and lip smacking during...

Predation can have major effects on vertebrate population dynamics, including predator–prey cycles that occur on multiple time scales when predators switch between preferred and alternative prey and changes in the abundance of preferred prey when the availability of alternative prey changes. Predation has been an important selective force in primat...

Non-invasive measurement of urinary cortisol is a proven method of evaluating the impact of environmental stressors on wild primates. Variation in cortisol concentrations can reflect physiological stress, and prolonged elevation of circulating cortisol can significantly affect individual and population-level health. In a previous study, we found th...

Design: Observations of wild chimpanzees ( Pan troglodytes schweinfurthii) were conducted in Kibale National Park, Uganda, at the sites of Sebitoli and Ngogo. Results: We report the first two cases of cleft lip in wild chimpanzees. Additionally, some other chimpanzees in the Sebitoli community show facial dysplasia and congenital anomalies, such...

Male mating tactics vary extensively in many primates. Some variation occurs because adolescent males often are sexually active but cannot invest heavily in mating effort because of their limited ability to compete directly with adults and because they are still investing in growth; consequently, most of their mating attempts may be surreptitious a...

Observations of chimpanzees (Pan troglodytes) and bonobos (Pan paniscus) provide valuable comparative data for understanding the significance of conspecific killing. Two kinds of hypothesis have been proposed. Lethal violence is sometimes concluded to be the result of adaptive strategies, such that killers ultimately gain fit-ness benefits by incre...

Primates and other mammals show measurable, heritable variation in behav-ioral traits such as gregariousness, timidity, and aggression. Connections among be-havior, environment, neuroanatomy, and genetics are complex, but small genetic differences can have large effects on behavioral phenotypes. One of the best examples of a single gene with large...

Chimpanzees (Pan troglodytes) hunt various primates, but concentrate on red colobus monkeys (Piliocolobus spp.) wherever the two species are sympatric. The extraordinarily large Ngogo chimpanzee community in Kibale National Park, Uganda, preys heavily on the local population of red colobus (P. tephrosceles). Census data showed a steep decline in th...

Recent research on primates and other taxa has shown that the relationships individuals form with members of the same sex affect their reproductive success. Evidence showing that intersexual relationships also influence reproduction, however, is more equivocal. Here, we show that male chimpanzees living in an exceptionally large community display l...

Long-term data are crucial for addressing questions about the behavior and ecology of chimpanzees because of their slow life histories. Despite the long history of field research on chimpanzees, the number of sites that have provided long-term data on multiple communities in the same population is still small. Long-term data on two habituated chimp...

In this chapter, we review some of the benefits and challenges of long-term primate field studies. We define long-term studies as those that cover a significant part of the study species' life cycle; in reality, many studies have already extended over multiple generations. We first provide a brief overview of the historical beginnings of modern pri...

The human apolipoprotein E (APOE) gene is polymorphic, with three primary alleles (E2, E3, E4) that differ at two key non-synonymous sites. These alleles are functionally different in how they bind to lipoproteins, and this genetic variation is associated with phenotypic variation for several medical traits, including cholesterol levels, cardiovasc...

Aligned primate APOE protein sequences. Human allele E3 is shown. Fullerton et al. refers to the chimpanzee sequence generated in reference #27. Other sequences were retrieved and translated from the respective primate genomes. The translation of the chimpanzee APOE amino acid sequence given in the Ensembl genome browser (“Chimp, Ensembl trans.”, E...

Primer sequences, product sizes and annealing temperatures for amplification protocols used in this study. See Figure 1 in main text for relative locations of primer pairs. (XLSX)

Fossils and molecular data are two independent sources of information that should in principle provide consistent inferences of when evolutionary lineages diverged. Here we use an alternative approach to genetic inference of species split times in recent human and ape evolution that is independent of the fossil record. We first use genetic parentag...

Researchers have documented infanticide by adult males in four wild chimpanzee populations. Males in three of these have killed infants from outside of their own communities, but most infanticides, including one from Kanyawara, in Kibale National Park, Uganda, took place within communities. Here we report two new cases of infanticide by male chimpa...

Chimpanzees (Pan troglodytes) are ecologically flexible omnivores with broad diets comprising many plant and animal foods, although they mostly eat fruit (including figs). Like other ecologically flexible nonhuman primates (e.g., baboons, Papio spp.) with broad diets, their diets vary across habitats. Much data on diets come from short studies that...

Highly frugivorous primates like chimpanzees (Pan trogolodytes) must contend with temporal variation in food abundance and quality by tracking fruit crops and relying more on alternative foods, some of them fallbacks, when fruit is scarce. We used behavioral data from 122 months between 1995 and 2009 plus 12 years of phenology records to investigat...

Some primate field studies have been on-going for decades, covering significant portions of individual life cycles or even multiple generations. In this volume, leading field workers report on the history and infrastructure of their projects in Madagascar, Africa, Asia and South America. More importantly, they provide summaries of their long-term r...

Habitat disturbance due to anthropogenic activities is a source of acute and chronic energetic stress in wild animals, including primates. Physiological responses to stress can compromise growth and reproduction, increase susceptibility to infection and lead to deleterious effects on health and conservation efforts. However, physiological measures...

Several recent studies have documented considerable intraspecific and intrapopulation ecological variation in primates. However, we generally lack an understanding of how such variability may be linked to concomitant demographic variation among groups or populations of the same species, particularly in regard to large-bodied and wide-ranging specie...

Male members of primate species that form multi-male groups typically invest considerable effort into attaining and maintaining high dominance rank. Aggressive behaviors are frequently employed to acquire and maintain dominance status, and testosterone has been considered the quintessential physiological moderator of such behaviors. Testosterone ca...

Chimpanzees make lethal coalitionary attacks on members of other groups [1 • Wilson M. • Wrangham R. Intergroup relations in chimpanzees.Annu. Rev. Anthropol. 2003; 32: 363-392 • Crossref • Scopus (249) • Google Scholar ]. This behavior generates considerable attention because it resembles lethal intergroup raiding in humans [2 • Wrangham R. The...

Dominance is a common, although not universal, characteristic of social relationships in nonhuman primates. One individual is dominant to another when it consistently wins the agonistic interactions between them. Attainment of high dominance rank can bring reproductive payoffs, mostly because it confers priority of access to monopolizable food sour...

Gorillas are one of our closest living relatives, the largest of all living primates, and teeter on the brink of extinction. These fascinating animals are the focus of this in-depth and comprehensive examination of gorilla biology. Gorilla Biology combines recent research in morphology, genetics and behavioural ecology to reveal the complexity and...

Identifying microbial pathogens with zoonotic potential in wild-living primates can be important to human health, as evidenced by human immunodeficiency viruses types 1 and 2 (HIV-1 and HIV-2) and Ebola virus. Simian foamy viruses (SFVs) are ancient retroviruses that infect Old and New World monkeys and apes. Although not known to cause disease, th...

GenBank accession numbers of newly obtained SFV sequences. (2.50 MB DOC)

Mitochondrial DNA analysis of primate fecal samples. (0.29 MB DOC)

Subspecies origin of chimpanzee fecal samples. Mitochondrial DNA sequences (498 bp D loop fragment) from SFVcpz positive chimpanzee fecal specimens were grouped into unique haplotypes (Table S1) and then compared to subspecies specific reference sequences by phylogenetic analysis. Sequences were analyzed using the Bayesian Markov chain Monte Carlo...

Chimpanzees make and use a wide variety of tools in the wild. The size and composition of their toolkits vary considerably among populations and at least to some extent within them. Chimpanzees at several well documented sites mostly use tools in extractive foraging, and extractive tool use can substantially increase their foraging efficiency. They...

Chimpanzees regularly hunt a variety of prey species. However, they rarely scavenge, which distinguishes chimpanzee carnivory from that of some modern hunter-gatherers and, presumably, at least some Plio-Pleistocene hominins. I use observations made over an 11-year period to document all known opportunities for scavenging encountered by chimpanzees...

Chimpanzees have complex and variable mating strategies, but most copulations occur when females with full sexual swellings are in parties with multiple males and mate with most or all of those males. Daily copulation rates for fully swollen females vary at different times of a female's cycle, among females, and across communities and populations....

Reconciliation, or peaceful postconflict interaction, can restore the usual pattern of interaction between social partners after open conflict has disrupted it—i.e., it can resolve conflicts. Researchers have documented reconciliation in >20 primate species, but the tendency to reconcile typically varies among dyads and dyad classes. The valuable-r...

Chimpanzees (Pan troglodytes) have hostile intergroup relations throughout most or all of their geographic range. Hostilities include aggressive encounters between members of neighboring communities during foraging and during patrols in which members of one community search for neighbors near territory boundaries. Attacks on neighbors involve coali...

The emergence of the genus Homo is widely linked to the colonization of 'new' highly seasonal savannah habitats. However, until recently, our understanding of the possible impact of seasonality on this shift has been limited because we have little general knowledge of how seasonality affects the lives of primates. This 2005 book documents the exten...

Territorial boundary patrols are a distinctive and unique aspect of wild chimpanzee, Pan troglodytes, behaviour. Although patrolling has been frequently observed in nature and several proposed functional explanations for it exist, scant information is available regarding the proximate factors that affect this activity. We found that there is consid...

Leptin is considered to act as a signal relating somatic energetic status to the reproductive system. However, the nature of that signal and its relationship with male reproductive function across nonhuman primate species are unclear. We suggest that species-specific differences in leptin physiology may be related to the degree of environmental var...

In an attempt to describe hormone-behavior interactions in a sample of wild male chimpanzees, we quantified testosterone in 67 fecal samples obtained from 22 adult male chimpanzees at Ngogo, Kibale National Park, Uganda. A mixed-model methodology that controlled for age-class identified a significant positive association between testosterone levels...

Wild chimpanzees, Pan troglodytes, show regional differences in feeding [Boesch and Boesch‐Achermann, 2000], tool using [McGrew, 1992], grooming [Nakamura et al., 2000], courtship [Nishida et al., 1999] and vocal communication [Mitani et al., 1992]. Comparisons have revealed at least 39 behavioural differences among chimpanzee populations [W...

Intercommunity coalitionary killing of adult and adolescent males has been documented in two chimpanzee communities in the wild, and it was strongly suspected in a third. It may increase survivorship for the attackers, their mates, and their offspring by reducing the combined strength of hostile neighbors and/or by increasing territory size and foo...

Simian immunodeficiency virus of chimpanzees (SIVcpz) is the immediate precursor to human immunodeficiency virus type 1 (HIV-1), yet remarkably, the distribution and prevalence of SIVcpz in wild ape populations are unknown. Studies of SIVcpz infection rates in wild chimpanzees are complicated by the species' endangered status and by its geographic...

Infanticide by males has been recorded in four chimpanzee populations, including that in Kibale National Park, Uganda. Some infanticidal attacks occur during inter-community aggression. The sexual selection hypothesis does not easily explain these attacks because they may not directly increase male mating opportunities. However, females in the atta...

Male chimpanzees, Pan troglodytes, are well known for affiliating and cooperating in a variety of behavioural contexts. Prior field research indicates that maternal kinship does not affect patterns of affiliation and cooperation by males in the same social group. Two questions remain unclear from this finding. First, why do male chimpanzees not bia...

Chimpanzees (Pan troglodytes) and bonobos (Pan paniscus), otherwise known as pygmy chimpanzees, are the only two species of the genus Pan. As they are our nearest relatives, there has been much research devoted to investigating the similarities and differences between them. This book offers an extensive review of the most recent observations to com...

Chimpanzees have always been of special interest to anthropologists. As our closest living relatives,(1-3) they provide the standard against which to assess human uniqueness and information regarding the changes that must have occurred during the course of human evolution. Given these circumstances, it is not surprising that chimpanzees have been s...

Social relationships in nonhuman primates result from investments that individuals make while pursuing tness-maximizing strategies. These strategies sometimes include social exchange, either reciprocity (exchange of the same acts) or interchange (exchange of different acts). Individuals in many species may negotiate for services in biological marke...

Chimpanzees (Pan troglodytes) prey on a variety of vertebrates, mostly on red colobus (Procolobus spp.) where the two species are sympatric. Variation across population occurs in hunting frequency and success, in whether hunting is cooperative, i.e., payoffs to individual hunters increase with group size, and in the extent to which hunters coordina...

Wild chimpanzees, Pan troglodytes, frequently hunt and share meat. Despite widespread interest and considerable study, continued controversy exists regarding the factors that influence chimpanzee hunting decisions and meat sharing. Three hypotheses invoke the importance of ecological, reproductive and social factors. A nutritional shortfall hypothe...

Chimpanzees are among the few mammals that engage in lethal coalitionary aggression between groups. Most attacks on neighbors occur when parties made up mostly of adult males patrol boundaries of their community's range. Patrols have time, energy, and opportunity costs, and entail some risks despite the tendency of males to attack only when they gr...

Allogrooming serves many social functions in primates. Grooming can help individuals to service social relationships generally, sometimes reciprocally, and may be particularly important in the development and maintenance of alliances. However, time constraints limit the number of partners with whom one individual can groom enough to maintain cooper...

Allogrooming contributes to the development and maintenance of social relationships, including those that involve alliances, in many primate species. Variation in relatedness, dominance rank, and other factors can produce variation in the value of others as grooming partners. Several models have been developed to account for variation in the distri...

Wild chimpanzees form temporary parties that vary in size and composition. Previous studies have revealed considerable intraspecific variation in party compositions. We examined patterns of association among age, sex, and reproductive classes of chimpanzees at Ngogo in the Kibale National Park, Uganda. We employed a class-based association index an...

We investigated hunting in an unusually large community of wild chimpanzees at Ngogo in the Kibale National Park, Uganda. Aspects of predation were recorded with respect to the prey, the predators, and hunting episodes. During 23 months of observation, the Ngogo chimpanzees caught 128 prey items from four primate and three ungulate species. Chimpan...

The abundance of food, especially that of fruit and often that of young leaves, varies considerably over time for most primates. This variation can depend on or be independent of seasonality in rainfall. Mountain gorillas (Gorilla gorilla beringei) in the Virungas are exceptional: their habitat contains almost no edible fruit, and they mostly eat p...

Cooperative mate guarding by males is unusual in mammals and birds, largely because fertilizations are non-shareable. Chimpanzees live in fission-fusion communities that have cores of philopatric males who cooperate in inter-group aggression and in defending access to the females in their community. Male contest mating competition is restrained wit...

Visually attending to conspecifics can give group-living primates important ecological information, help them to anticipate the behavior of others and to regulate interactions with them, and provide other valuable social information. Variation in the importance and quality of social relationships should influence the way individuals selectively att...

Mountain gorillas are highly folivorous. Food is abundant and perennially available in much of their habitat. Still, limited research has shown that single gorilla groups heavily used areas where food biomass and quality were relatively high and where they met daily nutritional needs with relatively low foraging effort. Also, ecological factors inf...

Resource depression caused by current feeding and the rate of resource renewal should influence foragers' decisions about when to revisit foraging areas. Adjustment of foraging paths and revisit rates should be particularly important when resources renew slowly. Foragers can also benefit by returning more often to highly profitable than to less pro...

Bonobo, the Forgotten Ape by F. de Waal University of California Press, 1997. £39.95 hbk (210 pages) ISBN 0 520 20535 9.

Considerable interspecific variation in female social relationships occurs in gregarious primates, particularly with regard to agonism and cooperation between females and to the quality of female relationships with males. This variation exists alongside variation in female philopatry and dispersal. Socioecological theories have tried to explain var...

Non-maternal infant care among nonhuman primates has frequently been investigated from the perspective of the caretaker. Here we examine whether allocaretaking behavior provides direct reproductive benefits to mothers. Comparative analyses that control for the effects of allometry and phylogeny reveal that allocaretaking behavior correlates with re...

Data on a large sample of interventions that individuals in two mountain gorilla (Gorilla gorilla beringei) groups made in agonistic interactions between others corroborate and extend earlier analyses in several ways. Related females supported each other as often as those in some female-bonded primates and maintained alliances while they resided to...

Females in some mountain gorilla groups can be ranked on the basis of decided, non-aggressive approach-retreat interactions. However, data on four gorilla groups show that females do not form clear agonistic dominance hierarchies. Most aggressive interactions between females were undecided, and most dyads had undecided dominance relationships (Fig....

Previous research has shown that both ecological and social factors influence mountain gorilla habitat use. New data on habitat use by a male gorilla and by a group confirm that male mating competition influences short- and long-term habitat use patterns, and show that its influence can supersede that of ecological factors on a long-term basis. Whe...

Female transfer is common in mountain gorillas, but most adult females reside with female relatives for at least some of their lives. In four mountain gorilla social groups, co-resident relatives had higher rates of affiliative interaction and lower rates of aggressive interaction, and were more tolerant of each other, than non-relatives. These dif...

Adult males are important social partners for all females in mountain gorilla social groups, but male-female relationships can vary in association with variation in female residence status, male age and mating status, and relatedness. Such variation occurred in a large group observed over a 3-year period. All females associated and interacted affil...

Patterns of home range use by a mountain gorilla group are examined here in relation to variation in food abundance and quality, diet quality and rainfall, to interactions between different social units and to the distribution of hazards (poaching risk). Variation in habitat quality influenced both long-term area occupation densities and shorter-te...