Vigilance and Collective Detection of Predators in Degus (Octodon degus)

Abstract

Individuals of social and partially social species typically reduce their vigilance activity when foraging in groups. As a result, per capita risk of predation decreases and individuals allocate more time to foraging and other fitness rewarding activities. Reduction of per capita risk is hypothesized to occur because there are more individuals to detect potential predators. If so, collective (i.e. total) vigilance is expected to increase with foraging group size. Increased surveillance during group foraging may occur if group members scan independently of one another, or sequentially to avoid the overlapping of their vigilance bouts. Intriguingly, such coordinated vigilance assumes that individuals monitor not only the presence, but the vigilance behaviour of group mates. We used seasonal records on time budget and grouping patterns of individually marked degus (Octodon degus), a social rodent, to examine if (a) individual vigilance decreases and/or foraging increases with group size, (b) collective vigilance increases with group size and (c) foraging degus coordinate their vigilance. When foraging, degus decreased their individual vigilance and increased their foraging time when in larger groups. Despite this, degus in larger groups increased their collective vigilance, supporting the hypothesis that socially foraging degus decrease predation risk through an improved ability to detect and escape potential predators. Additionally, patterns of collective vigilance suggested that degus scan independently of each other and so, they do not coordinate their vigilance to prevent its temporal overlapping. This finding does not support that foraging degus monitor the vigilance activity of group mates.

Spatial properties of a forest buffalo herd and individual positioning as a response to environmental cues and social behaviour

“…The trade-off between these costs and benefits can be a major strength determining the spatial properties of animal groups (e.g., Parrish and Edelstein-Keshet 1999;Ebensperger et al 2006;Hirsch 2007;Morrell and James 2008). For example, previous studies have demonstrated that two of the most important factors influencing animal group size (the number of individuals in the group) and density are the presence of effective mechanisms for reducing predation (Krause and Ruxton 2002;Ioannou et al 2007), and feeding competition (reviewed in Hirsch 2007).…”

Spatio-temporal vigilance architecture of an Australian flying-fox colony

“…Females, however, generally spent considerably less time on social vigilance than males, as described for white-faced capuchins (Cebus capucinus) in Costa Rica (Rose and Fedigan 1995). In previous studies that did not distinguish between functions of vigilance, males have been found to be more vigilant than or equally vigilant to females in a range of mammals such as primates (Cheney and Seyfarth 1981;Boinski 1988;van Schaik and van Noordwijk 1989;Koenig 1998;Steenbeek et al 1999) and ungulates (Prins and Iason 1989;Burger and Gochfeld 1994) as well as birds (Waite 1987;Domenech and Senar 1999); however, some studies differed (Burger and Gochfeld 1994;Ebensperger et al 2006). Seasonal changes in vigilance have also been observed (Ginnett and Demment 1997).…”

Interactions among social monitoring, anti-predator vigilance and group size in eastern grey kangaroos

“…Several studies on both birds and mammals have shown that individuals scan somewhat synchronously (Ebensperger et al 2006;Beauchamp 2009). Ruxton & Roberts (1999) argued that, even if group members act independently of one another, we might expect synchronization of vigilant acts of group members when, for instance, a potential danger, acting as an extra-group synchronizer, has been detected by each individual at the same time.…”