If it is one of twins it may weigh 13 or 4 pounds, if born singly, between 25 and 35 pounds. Helpless at birth, calves are secluded for a couple of days. The voice of a newborn calf is a low grunt, but after a few days it develops a strident wail that is almost human. At the age of only a few days the reddish-brown calf can outrun a man and swim readily. Of all North American animals, the moose calf gains weight the fastest, up to 2 pounds per day, and later in the summer may begin to put on as much as 5 pounds per day.
Calves stay with the cow for a full year, sometimes longer.
A bull calf may develop button antlers during its first year and the new antlers are grown each summer and shed each autumn. Mature animals usually shed their antlers in November, but younger bulls may carry theirs until December. During the period of growth the antlers are soft and spongy, with blood vessels running through them, and covered with a velvety skin. By late August or early September the antlers are fully developed and are hard and bony. The velvet dries and the bulls rub it off against tree trunks and willow brush.