Sympatric howler monkeys and spider monkeys are large-bodied primates that generally occupy primary forest with large fruiting trees that can provide sleeping sites and sufficient fruit supply (Dunn et al., 2009; Asensio et al., 2012). Spider monkeys are diurnal frugivores that can travel across large areas in search of food. Consequently, ranging and behaviour can vary considerably in relation to fruit availability (Asensio et al., 2012; Pinacho-Guendulain & Ramos-Fernández, 2017; Reyna-Hurtado et al., 2017). Howler monkeys are folivore-frugivores and although diurnal, they exhibit little activity during the day, and spend up to 80% of their day resting (Estrada et al 1999; Pavelka & Knopff 2004). Howler monkey inactivity is likely due to the high percentage of toxin-loaded mature leaves in their diet and fermentative digestion, which are energetically demanding. However, howler monkeys are reported to preferentially feed on ripe fruit when available, which can account for up to 80% of the diet during certain months of the year (Estrada et al. 1999; Pavelka & Knopff 2004). Due their adaptable diet, howler monkeys can live at high densities in relatively small home ranges where they adapt their diet rather than their ranging in response to fruit availability (Reyna-Hurtado et al., 2017).

There are notable sex-differences in the quality of social relationships and the type of social interactions exchanged by male and female spider monkeys (Slater et al., 2009). Unlike other primates, spider monkeys rarely engage in social grooming and have a unique suite of friendly behaviour consisting of embraces, kisses and pectoral sniffs. Rates of friendly behaviour and aggression vary considerably between male-male, male-female and female-female dyads and can provide insight into the strength of social bonds (Slater et al., 2009, Schaffner et al., 2012. Aggression between males is generally rare, and males direct the vast majority of their aggression towards females (Slater et al., 2008). Female aggression also occurs relatively infrequently, but when it does occur it is generally between adult females in the context of feeding (Asensio et al., 2008; Slater et al., 2009). In comparison, howler monkeys interact very little, and indications of social bonds are best determined by patterns of proximity rather than social interactions (Corewyn & Pavelka, 2007). Patterns of proximity indicate that the strongest social bonds within troops are between adult males and females, especially females with young infants (Corewyn & Pavelka, 2007).

A large community of spider monkeys and two troops of howler monkeys can be found in the same geographical area adjacent to the unexcavated ruins of El Ramonal in the Calakmul Biosphere Reserve. Food availability within their home ranges can be assessed using a phenology trail and both species are habituated to human presence permitting behavioural observations of the diet, activity budgets, ranging, habitat use and social interactions. The aim of the long-term study is to understand how each species adapts to fluctuations in fruit availability and to compare differences in behaviour between the two sympatric species.

Extended Dissertation Summary

If you would like to do a dissertation or thesis with us but your university hasn’t started dissertation planning or the project selection process, that’s no problem. You can cancel your expedition with zero cancellation charges up until the 15th of April of if you provide documentation from your university saying that they won’t support completing a dissertation project with us.