lar 1996c). Although this spacing arrangement would sug-
gest a promiscuous mating system, only one male sires all
offspring in a given litter (Topping and Millar 1998). The
Allegheny woodrat of the Appalachian Mountains in the
eastern United States apparently lives in colonies (Castle-
berry et al. 2001), although little information could be
found on proximity of individuals to one another or on
crevice usage within an outcrop. Both of these woodrats
cache food (Smith 1997; Castleberry et al. 2001).
Caviidae
The rock cavy inhabits rock outcrops in the semiarid
Caatinga of northeastern Brazil (Lacher 1981). Field obser-
vations suggest that rock cavy males defend rockpiles in-
habited by more than one female in a resource defense
polygyny type of mating strategy (Lacher 1981). Such a hy-
pothesis was supported by the observation of a skewed op-
erational sex ratio in the field (three males : fifteen females;
Lacher 1981). Additional evidence on wild and captive an-
imals supports the notion that the rock cavy is social; in the
field, groups of up to five individuals have been observed in
one small area (Streilein 1982) and in captivity males pro-
vide parental care (Tasse 1986).
Chinchillidae
The Chilean chinchilla (Chinchilla laniger) inhabits the
rugged, barren mountain ranges of north-central Chile (Spo-
torno et al. 2004). The Chilean chinchilla lives in colonies
of up to 500 individuals (Spotorno et al. 2004) with several
pairs reportedly coinhabiting the same den (Rice 1988). The
distribution of the Chilean chinchilla is reliant on the avail-
ability of suitable rocky habitat (Spotorno et al. 2004). The
Chilean chinchilla was severely hunted in the past for its fur
and is now considered endangered, while its congener the
short-tailed chinchilla (C. brevicaudata) is already thought
to be extinct in the wild (Jimenez 1996).
The northern mountain viscacha (Lagidium peruanum)
lives in rock outcrops and cliffs in the altiplano of south-
western South America (Rowlands 1974). Northern moun-
tain viscachas are highly gregarious, living in colonies of
up to seventy-five individuals where rock formations are
able to support such numbers (Pearson 1948). Each col-
ony is composed of family groups that contain between two
and five individuals each (usually an adult male, a parous
female, and offspring of varying ages). These family groups
are located in close proximity to one another, although
there is very little aggression between them most of the
year. During the breeding season, however, aggression lev-
els within the colony increase substantially; females appar-
ently evict adult breeding males from their family group
and aggressively attack any who approach them, while
males exhibit promiscuous behavior and attempt to guard
females from other males. Males are allowed to reassoci-
ate with females once again after the females have become
pregnant (Pearson 1948). The social group structure of the
other mountain viscachas (L. wolffsohniand L. boxi) have
also been described as colonial, although L. boxiis thought
to be more irascible than L. peruanum(Rowlands 1974;
Walker 2001, as cited in Walker et al. 2003).Capromyidae
The Jamaican hutia (Geocapromys brownii) and the Ba-
haman hutia (G. ingrahami) live in limestone crevices on
their respective islands (Clough 1974; Nadachowski and
Mead 1999b). Observations in the wild are scant for both
species. Observations of captive Bahaman hutias before
and after their release into the wild suggest that this species
lives in small family groups of between two and six indi-
viduals (sometimes up to ten individuals; Nadachowski and
Mead 1999b). Captive studies of the Jamaican hutia indi-
cate that this species is also likely to be gregarious (Clough
1972; Howe 1974). Captive studies also suggest that both
hutia species may live in paired social groups that contain
only one breeding female (Howe and Clough 1971; Oliver
et al. 1986).Abrocomidae
The genus Abrocoma(chinchilla rats) contains six species
that are very closely allied within the Abrocoma cinerea
species complex (Braun and Mares 2002). These six species
are distributed throughout arid, rocky areas in west-central
South America and have specific morphological adapta-
tions for living in rocky habitat, including padded feet and
reduced claws (Braun and Mares 2002). Five of the six
members of this species complex (all except A. cinerea) ap-
pear to be obligate rock-specialists (table 35.2; Braun and
Mares 2002). Abrocoma cinereais exceptional because, al-
though it usually associates with rocks, it sometimes lives
in crevices, but at other times digs its own burrow (Braun
and Mares 2002). Abrocoma cinereais reported to live in
small colonies. The social structure of the five other species
is unknown, although the presence of extremely large la-
trine piles in fissures inhabited by Abrocoma vaccarumsug-
gest that this species may also live in colonies (Braun and
Mares 1996).Petromuridae
The dassie rat lives in rock outcrops in Angola, Namibia,
and South Africa (Nowak 1991). The dassie rat is a diur-Socioecology of Rock-Dwelling Rodents 423