The male of several different animals is called a buck, including some kinds of deer, antelope and goats. You may also be interested in a horse's buck.
Most male birds are called cocks. Sometimes the word is in the common name of the bird, such as the peacock. Male birds tend to have much brighter coloured feathers than female birds, or hens.
A colt is a young male horse, generally one under four years old. The colt in the picture is one year old.