Lancia 1979; Hodgdon and Lancia 1983; Busher 1975,
1980, 1983a, 1983b; Busher and Jenkins 1985; Patenaude
1983; Patenaude and Bovet 1983, 1984; Buech 1987, 1995;
Woodard 1994; Sharpe and Rosell 2003). Since the evo-
lution and maintenance of the monogamous family group
involves balancing reproductive advantages for both the
adult male and female, it is imperative to examine their be-
havioral roles in the family group. As is the case with all
mammals, the adult female invests heavily in her young dur-
ing the relatively long period of gestation (approximately
100 days) and subsequent period of nursing (6 – 8 weeks).
However, it is critical to examine how the other family
members, especially the adult male, invest in the group.
Beaver social behavior: An overview
Comparisons between studies of marked beavers (where the
age and sex of each beaver is known) are difficult, due to
habitat and climatic differences at research sites or meth-
odological differences. Additionally, due to the goal of an
individual project, some specific behaviors may be over- or
underrepresented. Regardless of differences between stud-
ies, it is possible to find a general pattern of beaver behav-
ior within a family group.
Beaver behaviors can be categorized as those involved
with personal maintenance (cutting food and feeding,
grooming, and swimming associated with feeding), colony
maintenance (construction of dams, lodges, and burrows,
food caching, and bringing food to the lodge in the sum-
mer), and social interactions. Subadult beavers, especially
kits, generally engage in more personal maintenance be-
haviors than adults, while the adults perform more colony
maintenance behaviors. The degree of social interaction de-
clines as beavers mature. Nondispersing two-year-old bea-
vers have behavioral patterns more similar to adults and
yearlings than to kits (Hodgdon 1978; Busher 1980, 1983b;
Woodard 1994).
Within the social group the most common dominance
hierarchy is based on age, with adults dominant to younger
animals (Busher 1983a; Hodgdon and Lancia 1983). Only
Hodgdon and Larson (1973) reported a hierarchy in which
the adult female was dominant to the adult male, and this
was based on data from one family in one season. How-
ever, no other study found any evidence of the adult fe-
male being dominant to the adult male (Svendsen 1980b;
Busher 1980, 1983a; Brady and Svendsen 1981; Buech
1987, 1995). Female dominance over males in captive Eur-
asian beavers has been observed during the formation of the
pair bond. However, after the pair formed no sexual dom-
inance was observed (Wilsson 1971).
Monogamy in beavers has been linked with female ag-
gression (Wittenberger and Tilson 1980), yet this was based
on data from only two studies (Wilsson 1971; Hodgdon
and Larson 1973). However, there is little if any evidence
from other behavioral studies that female aggression and or
dominance exists in beaver families; in most groups the
adult male and female are codominant. It may be true that
female aggression and dominance can facilitate the forma-
tion of the pair bond, but adult female dominance within
an existing family has not been adequately documented.
Studies designed to test hypotheses relating to pair bond
formation and colony organization based on female domi-
nance would provide additional insight into this problem.Social behavior and maintenance of the mating system
While the importance of biparental investment in evolving
and shaping monogamous mating systems has recently been
questioned (Brotherton and Rhodes 1996; Brotherton and
Komers 2003), the construction activities and social orga-
nization of the beaver may require increased levels of bi-
parental care. One of the major questions regarding beaver
social organization and the mating system involves adult
male investment in the family group.
A study of the North American beaver in Minnesota re-
vealed that during the active period (generally 1800 hours –
0600 hours) adult females invested 6.5 hours daily to pa-
rental care and accounted for 58% of the total care during
the open-water season. Adult males allocated 5.2 hours of
time to behaviors associated with parental care and con-
tributed 42% of the total care (Buech 1987). In the Eur-
asian beaver, pairs of adult male and female beavers were
only different in the amount of time they allocated to travel;
their overall time budgets were not significantly different
(Sharpe and Rosell 2003). These data are consistent with
hypotheses regarding parental investment and monogamy
(Trivers 1972). Additional data suggest that adult males in-
vest in the family primarily by the performance of three ma-
jor types of behavior: (1) construction behaviors; (2) scent
marking and territorial behavior; and (3) alarm behaviors
(Busher 1980; Hodgdon and Lancia 1983; Woodard 1994).Construction behaviors
Beavers physically alter their environment through complex
construction activities, which represent a major source of
investment in the territory. Beavers invest in a specific area
by constructing dams, which create ponds, the construction
of lodges, and, in northern latitudes, by the construction of
a winter food cache (Jenkins and Busher 1979; Busher and
Hartman 2001). Both adults in a family group have been ob-
served actively performing construction behaviors, although
data from different studies are not consistent (table 24.1).
Because of methodological differences in data collection be-284 Chapter Twenty-Four