Researchers have long been observing nonhuman primates in diverse settings, from wildlife reserves to laboratories, but predominantly with intentions of understanding animal behavior in the wild without the influence of confounding variables. As a result, scholars justified the exclusion of habitats disturbed by anthropogenic influences (human activity), often failing to report on the qualitative or quantitative aspects of anthropogenic influences in habitats to publish studies with the most socio ecological validity (Fuentes & Riley, 2011). Recent observations have led researchers to believe that the understanding of behavioral flexibility in the anthropogenic habitat is pertinent to understanding social cognition even with nonhuman primates dwelling in the most minimally influenced areas (Nowak et al., 2014). Alongside the rapid expansion of anthropogenically-influenced habitats, the rejection of this commonplace exclusion generated a new area of study, ethnoprimatology (Fuentes & Riley, 2011). Investigators intended to advocate for a more holistic approach to studying humans and nonhuman primates interconnected both ecologically and culturally in their shared human-modified habitats (Fuentes & Riley, 2011). Within this discipline, researchers have found that nonhuman primates are ubiquitously experiencing environmental pressures to adapt on a local level, characterized by variation in subsistence behaviors and/or socially transmitted innovations (van Schaik, 2013). This paper aims to review behavioral flexibility observed in nonhuman primates and its role in coping with anthropogenic influences. I provide examples of socio-ecological and risk-related response adaptations and I discuss their implications in conservation and future research. I discuss definitions of behavioral flexibility, research methods to study it, some recent research findings and their implications.

Behavioral flexibility is defined variably across studies. For example, McLennan et al. (2017) defines it across five categories. Behavioral flexibility was recorded in nonhuman primates in response to anthropogenic influences as: (a) change in diet, often through foraging in rubbish, or consuming novel food items; (b) socio ecological adjustments, consisting of changes in ranging activity, sleeping site, social organization, habitat use and reproduction; (c) risk-related responses such as cryptic behavior towards domestic dogs, cats and humans to avoid detection; (d) miscellaneous behaviors including use of human water sources for drinking or artificial structures for travel and resting; (e) general use of the anthropogenic habitat (McLennan et al., 2017). Although not widely adapted, researcher McKinney created a classification system for these anthropogenic influences and their respective levels of disturbance. A four-part system was developed encompassing landscape, dietary, human-nonhuman primate interface, and predation interference; each of these categories having 12 -16 rankings of disturbances (McKinney, 2015).

Behavioral flexibility has been studied mostly as part of evolution theory until recently. It was studied in nonhuman primates before the emergence of ethnoprimatology mostly within the context of subsistence behaviors to provide a model for the evolution of early hominids and development of culture (Alberts & Altmann, 2006). Research initially predicted that nonhuman primates with larger bodies and brains would prove more resilient in the face of ecological changes (Alberts & Altmann, 2006). For example, data collected in the 1960s on the Amboseli baboon population documented their population decline through a woodland die-off and their subsequent recovery; meanwhile the smaller Amboseli vervet monkey population declined drastically and continues to as a consequence of the same woodland die-off (Alberts & Altmann, 2006). The Amboseli baboons exhibited more behavioral flexibility in this sequence of events, i.e. a slow ecological change, showing little to no seasonality in reproduction and birth and infant mortality rates dependent on food scarcity (Alberts & Altmann, 2006). However, more recent publications have contested the replicability of this study if anthropogenic influences become the driving force of a dramatic and rapid ecological change (Alberts & Altmann, 2006; van Schaik, 2013). Larger-brained species are “demographically handicapped” by their slow growth rate; their high mobility and longer-lived nature leaving them vulnerable to extinction from an inability to quickly develop genetically anchored adaptations (van Schaik, 2013). In contrast, the vervet monkeys if confronted with a rapid ecological change would likely adapt through natural selection of genotypes from generation to generation not through social innovations (van Schaik, 2013).

Research methodology has also changed to reflect the inclusion of habitats affected by anthropogenic influences. Researchers must record the degree of habitat modification or anthropogenic surroundings to facilitate reliable cross-site comparisons of behavioral and ecological data collections and discern as many consequential effects as possible in conjunction with the mixed-methods approach for data collection on these behavioral adaptations (McKinney, 2015). Thus why McKinney developed a standardized classification system allowing for thousands of combinations (McKinney, 2015). Some of the most common influences are habitat change and loss, human contact, provisioning, and hunting (McKinney, 2015).