Communal burrowing in the hystricognath rodent, Octodon degus:: a benefit of sociality?

We examined the hypothesis that a main benefit of group-living in the semifossorial rodent, Octodon degus (Rodentia: Octodontidae), is to decrease individual cost of burrow construction. We contrasted the digging behavior of groups of three same-sex, adult-sized individuals with that of solitary degus. The behavior of singles and trios was recorded inside a large terrarium partially filled with natural soil and under controlled conditions of food, light, and temperature. The observation that degus in groups do not decrease their burrowing time or frequency of digging compared with solitary diggers does not support the hypothesis that communal burrowing is a primary cause of degu sociality. On the other hand, the observation that degus in groups removed significantly more soil per capita than solitary digging degus, and that grouped individuals coordinated their digging - group members burrowed mostly in the same sites and formed digging chains -, suggests that social burrowing may potentially reduce the cost of burrow construction in the long term. We suggest that such longterm benefits will be a consequence rather than a cause of degu group-living.