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Wood Bison
Reproduction
The breeding season occurs from mid-July to late
September, with the peak rutting period in early August.
Bulls are generally found in their own groups before the rut and enter
the mixed herds when cows come into oestrus.
Dominance among bulls is established by behavioural display, sparring
matches, and occasionally by violent fighting between evenly matched bulls.
With an upraised tail, a bull will usually give aggressive signals such
as head-bobbing, snorting, wallowing, and pawing. The roar of a rutting bull can
be heard up to a kilometre away.
 Sexual maturity is attained at 2 to 3 years of
age for both males and females, and while females usually produce their first
calf at age 3, males generally do not breed until they are at least 7 or 8 years
of age. Younger bulls are capable of
breeding but are prevented from doing so by older males.
Cows
give birth from April until July, but the peak of calving occurs in May.
One calf is usual and twins are extremely rare. At birth, calves have
reddish-tan coats which turn dark chocolate brown by about 3 months of age.
They nurse soon after birth, balancing on long spindly legs, and within
the same day can be seen bucking and running about.
Cows recognize their own calves by smell and chase away strange calves.
Although calves nibble on grass within a few days of birth, they continue
to nurse for 7 months or longer, gradually increasing forage intake until they
rely entirely on an adult diet of grasses, sedges, and other plant matter.
Mortality can be high during the first year. Young calves use up their limited fat reserves during the long cold
winter, and are not efficient at foraging or avoiding predators, particularly
wolves.
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