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Thesis title: Navigation patterns in black howler monkeys (Alouatta pigra) at Palenque National Park, Chiapas, Mexico
Start year: 2016
I aim to explore Primates ability to navigate within complex home ranges such as rainforests, which distribution of food resources is highly patchy and ephemeral. Coping with environmental heterogeneity might have led to the evolution of cognitive strategies that could allow to remember the location and to constantly follow up the state of feeding sources within their home range. Sophisticated spatial skills have been proposed to be linked to the evolution of human intelligence since efficient navigation strategies would provide fitness advantages to primates by saving time and energy that could be spent on other activities, such as mating or breeding, instead of foraging. Milton first exposed this “ecological brain hypothesis” in 1981, and since then an extensive body of research has reported multiple evidence across primate taxa pointing out that monkeys and apes know what, when and where to forage by using multiple sensory and cognitive strategies. In addition, navigation might depend on multiple ecological (ie. inter-branch connectivity, food availability, etc.) and social (ie. intergroup encounters, group size, etc.) factors as well, which can be as – or even more – important as primate spatial skills to make directional decisions while navigating.
By studying a wild population of an Endangered Neotropical Primate, the black howler monkey (Alouatta pigra), I will explore the spatial cognitive skills from a naturalistic approach. Even though Milton’s postulations were based partly on direct observations of howler monkeys, the study of navigation patterns in this species has been unexplored to date. Hence, I will describe important aspects of black howlers’ spatial cognition based on direct observations in the wild. First, I will assess the use of cognitive maps based either on coordinates or routes – or a combination of both. The use of a coordinate-based map would provide the primate with an aerial perspective of the space allowing flexible and efficient ranging patterns, whereas the use of a route-based map might constrain primate’s movements to a route network within their home range to reach feeding sources. Second, I will determine the role of ecological, social and cognitive factors at directional decisions occurrence. Goal-orientated travel bouts towards inter-group encounters or preferred feeding sites are expected to trigger abrupt directional changes. However, if directional changes appear to be repeatedly cluster in certain locations within the home range, black howlers could be using certain landmarks to orientate their movements towards goals as part of their egocentric perception of the space. Finally, I will follow up the phenological status of black howlers’ preferred fruit trees that differ in the synchronicity of their cycles. Black howlers are expected to remember which preferred tree species presents a synchronous phenological cycle (i.e. all the trees of the same species ripen at the same moment of the year) by visiting more often multiple trees of this species after detecting one of them ripening. Preferred trees with asynchronous phenological cycle are expected to be visited equally throughout the entire annual cycle.
Alouatta pigra, Cognitive maps, spatial cognition, movement decision-making, spatial memory, foraging strategies
Foraging ecology, Cognition, Intelligence evolution, Comparative psychology, Neotropical primates, Home range use