On the Relationship between Herbaceous Cover and Vigilance Activity of Degus (Octodon degus)

Abstract

A number of studies demonstrate that plant cover provides prey animals with refuges to decrease vulnerability to predators. However, others suggest plant cover to visually obstruct detection of predators or conspecifics. We suggest these seemingly conflicting results can, to some extent, be resolved if overhead vs. lateral cover are distinguished. We recorded seasonal variation in vigilance activity of a natural population of degus (Octodon degus), a diurnal, semi-subterranean and social rodent from central Chile. We used these data to determine whether cover provided by herbaceous vegetation is mostly obstructive. The height of herbaceous vegetation in the habitat of degus varied seasonally, and the ability of degus (estimated from human observers) to detect potential predators decreased when herbaceous vegetation was high. This effect was more important for degus using quadruped postures and when dealing with terrestrial simulated predators. Accordingly, degus adjusted the quality rather than the quantity of their vigilance activity: male and female degus allocated similarly more time to bipedal vigilance when the height of herbs was high. Such increase in bipedal vigilance seemed to occur at the expense of quadruped vigilance instead of foraging time. Collectively, these results support the hypothesis that cover of herbaceous vegetation is mostly obstructive to degus when active above ground, a finding that contrasts with previous evidence supporting that shrub cover provides refuges against predators. The differential effects of shrubs and herbs on degu vigilance are likely linked to differences in the costs and benefits associated with each cover type. For degus, shrubs may provide more overhead (protective) than lateral (obstructive) cover.

Importance of Burrow-Entrance Mounds of Gunnison's Prairie Dogs (Cynomys gunnisoni) for Vigilance and Mixing of Soil

“…As vegetation grows during summer, changing the rate of vigilance provides greater security. This is similar to shifts in vigilance with changes in vegetation observed in degus (Octodon degus; Ebensperger and Hurtado, 2005). 2) Vigilance is more frequent by individuals on the periphery than those in the interior of the colony, and vigilance activities by those on the periphery are directed outward from the colony (Verdolin and Slobodchikoff, 2002).…”

Influence of predation risk and plant structure on vigilance and intermittent locomotion in Microcavia australis (Rodentia, Caviidae)

“…Gentian violet was used to paint the cavies; this substance is not toxic and is used to cure fungi. Neither tagging nor painting has a negative effect for animal welfare, as corroborated by Hoogland (1981), Cassini (1989), Branch (1993), Meserve et al (1993), Hoogland (1995), Ebensperger and Hurtado (2005), and Ebensperger et al (2006).…”

“…Another antipredator behavior is the mode of locomotion employed by rodents, which plays a vital role in determining their ability to elude predators (Thompson 1985;Djawdan and Garland 1988;Taraborelli et al 2003a). The structural complexity of the habitat may affect movement behavior by: (1) physically impeding locomotion (Schooley et al 1996), (2) making movement more conspicuous and thus riskier (Brillhart and Kaufman 1991;Borruel et al unpublished data), (3) providing a higher density of resources, hence favoring lower speeds so that resource opportunities are not missed (Brownsmith 1977), (4) increasing protection against predators through hiding cover (Thompson 1982;Taraborelli et al 2003b), (5) increasing visual obstruction, thus reducing the ability to detect predators (Schooley et al 1996;Ebensperger and Hurtado 2005).…”

Difficulties in Monitoring Conspecifics Mediate the Effects of Visual Obstruction on the Level and Synchronization of Vigilance

“…Visual obstruction can thus interfere with vigilance and increase predation risk (Lima, 1987). Observational studies with naturally-occurring visual obstacles and experimental studies, in which the field of view is altered by the researchers, have typically documented an increase in vigilance with visual obstruction (Lima, 1992;Arenz and Leger, 1997;Lima and Bednekoff, 1999;Blumstein and Daniel, 2003;Whittingham et al, 2004;Butler et al, 2005;Ebensperger and Hurtado, 2005;Fernández-Juricic et al, 2005;Devereux et al, 2006;Bednekoff and Blumstein, 2009;Iribarren and Kotler, 2012) although there are exceptions (Lima, 1987;Foster-McDonald et al, 2006;Hannon et al, 2006;Hall et al, 2013).…”