After insects decline in August, caribou scatter apart and feed heavily on willow leaves and mushrooms to regain body weight. Identifying Sex Young bulls before the age of three are similar in appearance to female caribou. It is important to know that you can not determine the sex of the animal solely by the antler size or the color of the mane. Bull caribou have a penis sheath and will urinate in a forward direction. It is possible to encounter problems viewing the penis sheath on older bulls, when they are standing in brush or when an animal's stance blocks the view.
Cows have a vulva, brown or black in color, below the anus.
The vulva and anus are visible when the tail is up. If the tail is down, however, only a portion of the vulva can be seen. The caribou is the only member of the deer family in which both sexes grow antlers. Antlers on cows are generally smaller than bulls and have fewer than 15 points. The upper end of a large bull's antler may be heavily palmated.