groups, however, is unknown. Within social groups, indi-
viduals appear to cooperate in several ways. For example,
multiple animals contribute to the excavation of tunnels;
although tunnel construction is not as conspicuously coor-
dinated as it is in some social bathyergids (Jarvis and Sale
1971), participation by multiple individuals may reduce the
per capita energetic cost of tunnel construction or may al-
low the animals to excavate more extensive tunnel systems
than would be possible for lone individuals (Ebensperger
and Bozinovic 2000a). When above ground, the animals
alarm-call in response to predators and other apparent
threats (Fulk 1976; Yáñez 1976). Preliminary evidence sug-
gests that alarm calls differ with predator type (Cecchi et al.
2003) and these calls may serve to alert group-mates to per-
ceived dangers, thereby facilitating the survival of individu-
als with whom the caller lives and interacts. Finally, al-
lonursing of young has been observed among captive degus
(Ebensperger et al. 2002); field studies are currently under-
way to document this form of cooperative care of young
among free-living animals.
Example 2: Social structure in cururos
Cururos (Spalacopus cyanus) are subterranean octodon-
tids that are patchily distributed throughout central Chile
(fig. 34.3; Saavedra and Simonetti 2003). Perhaps more so
than the other species reviewed here, cururos exhibit con-
siderable intraspecific variation in ecology. Populations are
found in arid, coastal scrub habitat (where they may co-
occur with degus) as well as in mesic, montane meadows
(Contreras et al. 1987; Torres-Mura and Contreras 1998).
Associated with this range of habitat types are pronounced
differences in body mass, with adult males ranging from
ca. 80 g in arid areas to ca. 180 g in more mesic regions
(Contreras 1986; Lacey, Ebensperger, and Wieczorek, un-
published data). Given the conspicuous differences in the
floral communities characteristic of these habitat types, diet
composition also presumably varies substantially among
conspecifics, as does the proportion of the diet consisting
of surface-growing versus subterranean plant parts (Reig
1970; Torres-Mura 1990). As a result of this intraspecific
variation in habitats, studies of cururos provide a particu-
larly important opportunity to examine the effects of spe-
cific ecological variables on patterns of social structure.
In general, the natural history of cururos has been less
thoroughly documented than that of degus. With regard
to their annual reproductive cycle, cururos are thought to
breed between June and March in coastal areas, with the
duration of reproductive activity expected to be shorter in
Andean populations (Unda et al. 1980). Whether individual
females rear more than one litter of young per year remains
unknown, and this and other aspects of the annual repro-
ductive cycle may vary among populations and habitats.
Based on observations of mating and parturition in captive
animals, gestation lasts for approximately 77 days (Begall
et al. 1999). Like degus, neonatal cururos are precocial, but
the timing of several critical ontogenetic events appears to
be somewhat delayed relative to degus. For example, al-
though the young are born with pelage, their eyes do not
open until 2 to 8 days after birth (Begall et al. 1999; but see
Torres-Mura and Contreras 1998). Pups do not begin con-
suming solid food until ca. 18 days after birth and, in cap-
tivity, weaning does not occur until pups are 60 days old
(Begall et al. 1999). Thus, while cururos follow the general
octodontid pattern of producing precocial young, postpar-
turition development of pups is not as rapid in this species
as in degus.
All populations of cururos surveyed to date are social,
meaning that multiple adults share the same burrow sys-
tem (Reig 1970; Begall et al. 1999; Lacey, Ebensperger and
Wieczorek, unpublished data). Up to ten adults, including
multiple animals of both sexes, have been captured in the
same burrow system (Reig 1970; Begall et al. 1999). Ani-
mals resident in the same burrow system share a single nest408 Chapter Thirty-Four
Figure 34.3 Geographic distribution of Spalacopus cyanus. Range data were
compiled from Redford and Eisenberg (1992). Inset: photo of S. cyanus,taken
by Luis A. Ebensperger.