Detecting predators and locating competitors while foraging: an experimental study of a medium-sized herbivore in an African savanna

Abstract

Vigilance allows individuals to escape from predators, but it also reduces time for other activities which determine fitness, in particular resource acquisition. The principles determining how prey trade time between the detection of predators and food acquisition are not fully understood, particularly in herbivores because of many potential confounding factors (such as group size), and the ability of these animals to be vigilant while handling food. We designed a fertilization experiment to manipulate the quality of resources, and compared awareness (distinguishing apprehensive foraging and vigilance) of wild impalas (Aepyceros melampus) foraging on patches of different grass height and quality in a wilderness area with a full community of predators. While handling food, these animals can allocate time to other functions. The impalas were aware of their environment less often when on good food patches and when the grass was short. The animals spent more time in apprehensive foraging when grass was tall, and no other variable affected apprehensive behavior. The probability of exhibiting a vigilance posture decreased with group size. The interaction between grass height and patch enrichment also affected the time spent in vigilance, suggesting that resource quality was the main driver when visibility is good, and the risk of predation the main driver when the risk is high. We discuss various possible mechanisms underlying the perception of predation risk: foraging strategy, opportunities for scrounging, and inter-individual interference. Overall, this experiment shows that improving patch quality modifies the trade-off between vigilance and foraging in favor of feeding, but vigilance remains ultimately driven by the visibility of predators by foragers within their feeding patches.

Predators, food and social context shape the types of vigilance exhibited by kangaroos

“…Carrying out multiple tasks simultaneously can reduce an animal's attention and efficiency with respect to predator detection (Dukas, 2002), and researchers have suggested that vigilance while handling food would reduce the chance of detecting a predator because of the noise resulting from the mastication process (Blanchard & Fritz, 2007;Fortin et al, 2004;. The investment of social foragers in these two types of vigilance has been shown to vary with predation risk, food resource characteristics, group size and the distance between foragers (Benhaim et al, 2008;Fern andez-Juricic, Beauchamp, & Bastain, 2007;Meer et al, 2012;Pays et al, 2012;.…”

“…handling or chewing) its food (hereafter termed 'vigilance with chewing') (e.g. Lima, Zollner, & Bednekoff, 1999;Meer, Pays, & Fritz, 2012;Pays et al, 2012;Robinson & Merrill, 2013). However, while differing in terms of their costs to foraging, these two types of vigilance may also differ in the quality of perception that they offer .…”

“…In fact, many species of birds and mammals are able to continue food ingestion by handling or chewing their food during vigilance periods (Baker, Stillman, Smart, Bullock, & Norris, 2011;Fortin, Boyce, Merrill, & Fryxell, 2004;Pays et al, 2012). In these species, it is therefore possible to distinguish a high-intensity form of vigilance in which the animal stops all activities and raises its head (hereafter termed 'vigilance without chewing') from a lower intensity form of vigilance during which the animal is vigilant while processing (i.e.…”

Activity Budgets of Impala (Aepyceros melampus) in Closed Environments: The Mukuvisi Woodland Experience, Zimbabwe

“…We argue that the level of provisioning and attraction for wildlife species in some systems may reduce seasonal variations in activity budgets of impala social groups. Observations made by Pays et al [15] indicate that improving forage patch quality modifies the trade-offs between vigilance and foraging in favour of feeding. Animals invest time in the acquisition of information about forage resources within their environmental setting thus affecting the proportion of time allocated to other activities [16].…”

A relação entre o bullying e os relacionamentos sociais num grupo de adolescentes brasileiros

“…A partir de um olhar etológico, podemos olhar a agressão como um comportamento social, mesmo sendo este agonístico. Ao compartilhar um mesmo ambiente com outros indivíduos da mesma espécie se obtém benefícios como a cooperação ativa com outros, ganhos na localização de alimento e diminuição do risco de predação (Bijleveld, van Gils, Jouta & Piersma, 2015;Josephs, Bonnell, Dostie, Barrett, Henzi, 2016;Pays et al, 2012). Mas na mesma medida a convivência em grupo implica custos como a disseminação de doenças, maior visibilidade aos predadores e o surgimento da competição pelos recursos (Altizer et al, 2003;Aureli & de Waal, 2000 (Simon & Lu, 2005;Waltes, Chiocchetti & Freitag, 2015).…”