Kudus are antelopes that are slightly larger than impalas. They are distinguished by their vertical markings on the side, spiral horns, and shoulder hump (used for high jumping).

The horns add a spiral every two years, so you can age the bucks based on this.
They exist right alongside the impalas throughout the park.
A younger male as evidenced by the smaller number of spirals on the horn.
A good shot of the side markings.