Abstract
BackgroundAlthough navigating along a network of routes might constrain animal movement flexibility, it may be an energetically efficient strategy. Routinely using the same route allows for visually monitoring of food resources, which might reduce the cognitive load and as such facilitate the process of movement decision-making. Similarly, locating routes in areas that avoid costly landscape attributes will enhance their overall energy balance. In this study we determined the benefits of route navigation in an energy minimiser arboreal primate, the black howler monkey (Alouatta pigra).MethodsWe monitored five neighbouring groups of black howler monkeys at Palenque National Park, Mexico from September 2016 through August 2017. We recorded the location of the focal group every 20 m and mapped all travel paths to establish a route network (N = 1528 travel bouts). We constructed linear mixed models to assess the influence of food resource distribution (N = 931 trees) and landscape attributes (slope, elevation and presence of canopy gaps) on the location of routes within a route network.ResultsThe number of food trees that fell within the visual detection distance from the route network was higher (mean: 156.1 ± SD 44.9) than randomly simulated locations (mean: 121.9 ± SD 46.4). Similarly, the number of food trees found within the monkey’s visual range per meter travelled increased, on overage, 0.35 ± SE 0.04 trees/m with increasing use of the route. In addition, route segments used at least twice were more likely to occur with increasing density of food resources and decreasing presence of canopy gaps. Route segments used at least four times were more likely to occur in elevated areas within the home ranges but only under conditions of reduced visual access to food resources.ConclusionsRoute navigation emerged as an efficient movement strategy in a group-living arboreal primate. Highly used route segments potentially increased visual access to food resources while avoiding energetically costly landscape features securing foraging success in a tropical rainforest.
Highlights
Navigating along a network of routes might constrain animal movement flexibility, it may be an energetically efficient strategy
Between 64.5 and 75.1% of the travel bouts fell within the habitual route network, which had a mean length of 3.2 ± Standard deviation (SD) 1.2 km per group (Fig. 1)
The number of Feeding Trees (FTs) that fell within the estimated visual range along route segments used twice was 0.07 ± 0.04 trees/m while it increased to 0.11 ± 0.05 trees/m in segments used four times and to 0.24 ± 0.20 in segments used seven times (Fig. 2)
Summary
Navigating along a network of routes might constrain animal movement flexibility, it may be an energetically efficient strategy. Animal movement strategies are influenced by individuals’ ability to acquire and process information, as well as the energetic requirements of traveling through the landscape [1,2,3]. Some animal species have been suggested to navigate using cognitive maps: mental representations coding spatio-temporal information of the space where they live in that permits efficient movement decisions [4,5,6,7,8]. The elements that construct such spatial representation are still debated [8], the ability to navigate flexibly in space has been suggested to be indicative of sophisticated cognitive maps and, enhanced cognitive abilities [9]. By following an established set of habitual routes animals and humans benefit from simplifying the decision-making process of movement while still securing foraging success [17]
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