American Bison - Buffalo Field Campaign

leave the herd prior to calving or give birth within the herd
(McHugh 1958). Similarly, for wood bison in the Mackenzie
Bison Sanctuary (MBS), females have been observed calving
in the midst of herds or in extreme isolation in the forest away
from any other animals (N.C. Larter, personal observation).
Birthing normally occurs while the female is lying down. The
mother typically consumes portions of the afterbirth as she
frees the calf from the membranes (Lott 2002; McHugh 1958).
The female licks amniotic fluid from the calf’s fur (Lott 2002).
Suckling begins shortly after birth and may last as long as
10 minutes (McHugh 1958); although there was a report of a
wood bison mother attacking the newborn calf during suckling
(Carbyn and Trottier 1987). The close contact between a
cow and calf begins to decline after the calf’s first week of
life (Green 1992). A calf is typically weaned by seven to eight
months of age, although nursing may extend beyond 12
months (Green et al. 1993). The longest associations among
bison are between cows and their female offspring; while male
offspring may remain with the cow through a second summer,
female offspring may remain with the cow through a third
summer (Green et al. 1989; Shaw and Carter 1988).
The cow may use quick charges or steady advances to defend
a calf against threats (Garretson 1938; Hornaday 1889; McHugh
1958). An isolated plains bison cow vigorously defended her
calf from a grizzly bear (Ursus arctos), even though the bear was
ultimately successful in killing the calf (Varley and Gunther 2002).
Similarly, an isolated cow vigorously defended the calf from
wolves (Canis lupus) (C. Freese, personal communication).
Cows and other members of mixed-sex and age groups may
cooperatively protect calves from predators. In response to the
approach of a grizzly bear, a mixed-sex and age group of adult
plains bison responded by facing the bear in a compact group,
with the calves running behind the adults (Gunther 1991). Wolves
preferentially attempt to prey upon wood bison mixed-sex and
age groups that include calves (Carbyn and Trottier 1987). During
wolf attacks, calves moved close to the cow, or
to other bison, or to the centre of the bison group
(Carbyn and Trottier 1987; 1988), although this
defensive response may break down when bison
groups move through forested areas that may
impede the movements of the calves (Carbyn and
Trottier 1988).
6.1.2.4 Horning and wallowing
All age and sex classes of bison engage in
behaviours referred to as horning and wallowing
(McHugh 1958). Horning involves an animal
Plate 6.2 Wallowing modifies the landscape. Photos:
Dwight Lutesy (inset) and John Gross.
rubbing an object, typically a shrub or small tree, with its
head, horns, neck, or shoulders (Coppedge and Shaw 1997).
Wallowing involves a bison rolling in dry loose ground (or
less frequently in wet ground) and tearing at the earth with
its horns and hooves as it rolls. Bison prefer to horn aromatic
shrubs and saplings (Coppedge and Shaw 1997; Edwards
1978; McHugh 1958; Meagher 1973), which may have insect
deterrent properties. Bison have even been observed rubbing
on treated telephone posts (Coppedge and Shaw 1997). Soper
(1941) observed that horning and rubbing were often associated
with harassment by insects. Like wallowing, horning may also
constitute aggressive display behaviour.
Bison of both sexes and all age classes engage in wallowing
behaviour throughout the year (Reynolds et al. 2003), although
sexually mature males wallow more frequently during the rut,
urinating in the wallow before pawing and rolling (Lott 2002;
McHugh 1958). Wallowing by mature males may stimulate
oestrus in females (Bowyer et al. 1998), and advertise a male’s
physical condition to other males (Lott 2002). Plains bison
may also wallow to cool themselves during the hot summer
months, or to achieve relief from biting insects (McMillan et al.
2000; Mooring and Samuel 1998). Catlin (in Hornaday 1889)
described bison creating wallows in areas with a high water
table and rolling in the wallow as it filled with water. The result
was pelage matted with mud and clay (Catlin in Hornaday 1889).
Coat shedding, rut, and insect harassment occur simultaneously
during the summer; therefore in the absence of controlled
experimentation, it is not possible to determine the relative
influence of these factors on the frequency of horning and
wallowing (Coppedge and Shaw 1997).
6.1.2.5 Movements
Plains bison frequently travel in single file along well-established
trails when moving between foraging patches (Garretson
1938; Hornaday 1889). Historically, plains bison undertook
American Bison: Status Survey and Conservation Guidelines 2010 41