photo courtesy of Tomas Plecenik and www.wildanimalsonline.com, <http://wildanimalsonline.com/mammals/degu.php>
An Example of Quadripedled Vigilance
Degus face a number of aerial and terrestrial predators including: black-chested buzzard eagles (Geranaetus melanoleucus), Harris’s hawks (Parabuteo unicintus), white-tailed kites (Elanus leucurus), American kestrels (Falco sparverius), Aplomado falcons (Falco femoralis), Culpeo foxes (Pseudoalopex culpaeus), Iguana lizards (Callopistes palluma), Long-tailed snakes (Philodryas chamissonis), barn owls (Tyto alba), and short-eared owls (Asio flammeus) (Fulk 1976; Ebensperger & Hurtado 2005). The range of both aerial and terrestrial predators sheds light on the great need for vigilance during foraging. Most adult degus do not live more than two years in the wild, as compared to 5-8 years in captivity (Ebensperger, Hurtado, & Valdivia 2006).
Like many other factors in a degu’s environment, the presence of predators varies greately according to season (Ebensperger & Hurtado 2005). Predators were four times more likely to be seen in autumn than in spring. Interestingly, the appearance of predators in the degu’s environment does not coincide with the births of pups, nor does it result in substantially more time being dedicated to vigilance activities. It does, however, result in a change in the quality of vigilance. During times of low predation threat vigilance was largely quadripedled (head raised, all four feet remain on the ground). Vigilance in high-predator months was more likely to be bipedaled (animals sit on haunches with torso raised). The increased energetic and time expense of the bipedaled position suggests that it provides higher quality vigilance during high risk months.
Seasonal variations in vegetation also affect vigilance. Depending on the type of vegetation, plant cover may enhance protection from predators or may hinder it (Hayes et al 2007; Ebensperger & Hurtado 2005). Overhead cover should be preferable as it provides protection from aerial predators without hindering lateral vision. Indeed, Hayes et al. (2007) found that degus living in areas with more overhead cover tended to move further from the burrow opening. Tall spring grasses, however, inhibit lateral vision while providing only limited overhead cover. In months of rapid grass growth, degus were more likely to exhibit bipedaled vigilance behaviors (Ebensperger & Hurtado 2005).
In addition to increasing the proportion of bipedaled vigilance, degus often forage in groups in high risk microhabitats and at high risk times of the year. This is especially the case for degus living in open microhabitats (Ebensperger & Wallem 2002). Tall grasses tended to discourage group foraging, perhaps because communication between group members is inhibited by obstructions to vision. Ebensperger, Hurtado & Ramos-Jiliberto (2006) found that as group size increased, individual vigilance decreased. This suggests that degus do rely on one another for increased vigilance benefit, which is more consistent with the “many eyes” hypothesis rather the selfish herd hypothesis. The ability to rely on others in the group depends on the use of almost instantaneous alarm calls to alert others in the group to predation threats. Degus do, in fact, use a number of different communicative vocalizations, including alarm calls, which are often used in the presence of low-flying, non-predatory birds as well as predatory birds. Fulk (1976) observed that these calls were not specific to the particular threat, but sounded in the presence of humans, dogs, and birds. It is important to note, however, that although degus relied on one another for group vigilance, there was no evidence of specific coordination of these behaviors between group members (Ebensberger, Hurtado & Ramos-Jiliberto 2006).
Not surprisingly, above ground activity is also influenced by the number and positions of burrow openings (Hayes et al 2007). The tail of a degu is adapted so that, if caught, will tear easily so that the animal can free itself (http://nationalzoo.si.edu/Animals/SmallMammals/fact-degu.cfm, April 2, 2008). Ultimately, however, it is the burrow system that provides most protection from predators. Fulk (1976) found that most above ground activity was spent on the “runways” between burrow openings (499). As was the case with vegitative cover, degus tended to move further away from the burrow as the number of burrow openings increased (Hayes et al. 2007). It is clear that access burrows, and more specifically access to burrow openings, are important effecters of above ground anti-predation behavior.
photo courtesy of Calvin J. Hamilton and www.scienceviews.com , <http://www.scienceviews.com/photo/mammals/Degu1.html>
This website was created in partial fulfilment of Biology 323, Animal Behavior in the Spring of 2008 by Mary La Montagne
For Questions, Comments, or Suggestions please email malamontagne@davidson.edu, or vecase@davidson.edu