Figure 34.2 Geographic distribution of Octodon degus. Range data were
compiled from Redford and Eisenberg (1992). Inset: photo of O. degus,taken
by Luis A. Ebensperger.
Example 1: Social structure in degus
Degus (Octodon degus) are medium-sized (ca. 180 g), diur-
nal octodontids that occur in semiarid and Mediterranean
habitats in north-central Chile (fig. 34.2; Woods and Bo-
raker 1975). Although degus construct underground bur-
rows and nest in subterranean chambers, the animals spend
a considerable portion of their time above ground, during
which they may travel up to several meters from the near-
est burrow entrance (Fulk 1976; Yáñez 1976; Vásquez et
al. 2002; Soto-Gamboa 2004). The animals forage exclu-
sively on surface-growing vegetation, including the leaves
of a variety of grasses, forbs, and, to a lesser extent, shrubs
(Fulk 1976; Mann 1978; Meserve et al. 1983, 1984). Young
leaves are preferred (Simonetti and Montenegro 1981),
which may reflect selection of food items of high nutritional
quality (e.g., high water, nitrogen content) and low fiber or
secondary plant metabolite content (Bozinovic 1995, 1997;
Torres-Contreras and Bozinovic 1997; Gutiérrez and Bozi-
novic 1998; Bozinovic and Torres-Contreras 1998).
Because the animals occur in habitats characterized by
seasonal precipitation, the availability of green vegetation
varies throughout the year; this variation appears to have
significant implications for other aspects of degu biology,
including annual patterns of reproduction. Degus typically
mate during the early winter (June –July), with parturi-
tion occurring during September – October (Contreras and
Bustos-Obregón 1977; Rojas et al. 1977; Meserve et al.
1984; Kenagy et al. 1999, Ebensperger and Hurtado 2005b).
Females in at least some populations are thought to undergo
a postpartum estrus (Rojas et al. 1977), resulting in the
production of a second litter of young during December –
January. Mean litter size is six pups (Veloso 1997). The
young are precocial; newborn degu pups have pelage and
their eyes are open (Reynolds and Wright 1979; Ebensper-
ger, unpublished data). Although the young quickly be-
come ambulatory and begin eating vegetation at about 6 to
10 days of age, they continue to nurse until they are ap-
proximately 4 weeks old (Reynolds and Wright 1979; Ve-
loso 1997). Based on the weights of field-caught animals,
juveniles first become active above ground about 3 – 4 weeks
after birth, after which they can frequently be observed in-
teracting with conspecifics while outside of their natal bur-
row system.
Degus are social, with groups consisting of two to five
adult females and their dependent young (Fulk 1976; Yá-
ñez 1976). The number of adult males per group is unclear;
while some accounts indicate only a single adult male per
group (Soto-Gamboa 2004), others suggest that groups con-
tain multiple adult males (Fulk 1976; Yáñez 1976). Mem-
bers of a social group share the same burrow system,
including a communal nest site (Soto-Gamboa 2004; Eben-
sperger et al. 2004). Genetic estimates of kinship indicate
that female nestmates are significantly more related to one
another than to randomly selected females in the popula-
tion, with a mean coefficient of relatedness among conest-
ing females of ca. 0.25 (Ebensperger et al. 2004). Evidence
of kin discrimination, however, is inconsistent. For example,
while preliminary observations of interactions among lab-
reared juveniles indicate that unfamiliar individuals display
less aggression toward siblings than nonsiblings (Márquez
et al. 2002), lab-reared pups do not associate more with
their mothers than with unrelated lactating females (White
et al. 1982), and captive females retrieve their own and un-
familiar pups indiscriminately (Ebensperger, unpublished
results). Ongoing field and laboratory studies of known
individuals should serve to clarify how kin discrimination
contributes to observed patterns of kin structure in this
species.
Typically, all adult female degus in a group produce off-
spring (Soto-Gamboa 2004; Ebensperger and Hurtado, un-
published data). How reproductive success is partitioned
among female nestmates or among the males in multi-maleSocial Structure in Octodontid and Ctenomyid Rodents 407