tween studies it is difficult to generalize about sexual dif-
ferences in construction behavior. However, adult females
have been observed to be more active than males in lodge
work, while adult males have been observed to be more
active in other construction behaviors (Hodgdon 1978;
Busher 1980; Buech 1987; Woodard 1994).
An additional problem is that beavers in different habi-
tats may not be involved in all construction activities. For
example, beavers living on large lakes and on large rivers do
not construct dams, and may not construct lodges (Buech
1987; Breck et al. 2001), and North American beavers liv-
ing at more southern latitudes or in areas not subjected
to freezing do not generally construct food caches. Food
cache construction may also be variable within a popula-
tion. Goran Hartman, studying the Eurasian beaver in Swe-
den, found that 33% (thirteen of thirty-nine) of families
in the same geographical area did not build a food cache
(G. Hartman, personal communication). However, what is
evident is that the adult male in a family group is actively
involved in construction behaviors; this represents a major
source of male parental investment.
Territorial behavior and scent communication
Beavers mark a territory by the construction of scent
mounds (fig. 24.4). These scent mounds consist of piles of
mud and vegetation, onto which beavers deposit the secre-
tions from their castor sacs and anal glands (Wilsson 1971;
Hodgdon 1978; Jenkins and Busher 1979; Svendsen 1980a;
Schulte 1993; Rosell and Nolet 1997). Castoreum, the fluid
from the castor sacs, is produced by urine passing through
the sacs and picking up the scent, and hundreds of com-
pounds have been identified in castoreum (Svendsen and
Huntsman 1988; Müller-Schwarze 1992; Tang et al. 1993,
1995). The secretion of the anal gland is oily, insoluble in
both water and ethanol, and has a strong odor (Svendsen
1978; Schulte and Müller-Schwarze 1999). The anal gland
secretion has been used to differentiate between the sexes
and between the two species (Schulte et al. 1995; Rosell and
Sun 1999).
Scent mounds are usually constructed near feeding sites,
active lodges, construction areas, and margins of territo-
ries (Wilsson 1971; Hodgdon 1978; Rosell et al. 1998). Al-
though scent mounds do not appear to keep transient bea-
vers out of existing territories (Wilsson 1971; Hodgdon
1978) they are most likely used to advertise the occupation
of an area (Aleksiuk 1968; Taylor 1970; Schulte and
Müller-Schwartz 1999).
Captive female Eurasian beavers usually marked first
and more frequently than males (Wilsson 1971), while in
a North American beaver population adults accounted for
74.3% of all scent marking, and males of all age classes scent
marked more than females of the same age class (Hodgdon
1978). In the same North American population, when pre-
sented with unfamiliar castoreum and anal gland secretion,
adult males had a significantly stronger response to un-Social Organization and Monogamy in the Beaver 285Table 24.1 Comparison of construction behaviors performed by adult male and female beavers
Lodge work Dam work Dam inspection Food cache Canal workReference Male Female Male Female Male Female Male Female Male Female
Hodgdon (1978)a 11.4 31.3 20.5 44.3 37.3 24.4 25 29.2 28.4 34
Busher (1980)b 0.5 2.0 3.3 2.4 17.4 13.8 0.5 0.3 n.a. n.a.
Buech (1987)c 8.5 1.1 n.a. n.a. n.a. n.a. 2.6 5.3 n.a. n.a.
Woodard (1994)c 0.04 0.05 9.77 2.45 0.7 0.6 n.a. n.a. n.a. n.a.
NOTE: n.a.a not available.
bHodgdon (1978) reported observations as the proportion of the behavior performed by each age-sex class.
cBusher (1980) reported observations as the frequency of occurrence of a behavior in relation to all behaviors.
Buech (1987) and Woodard (1994) reported observations in the form of time budgets.
Figure 24.4 A typical scent mound constructed by the North American beaver
(Castor canadensis), in Massachusetts. The mound consists of small sticks, leaves,
and mud, and a beaver will deposit scent on the top of the mound. Photograph
by Peter Busher.