by LYLE GLASS.
Two young pronghorn antelope bucks are sparring playfully by doing some head butting. As the bucks get older, the sparring becomes more malicious as they spar for breeding rights with the does.
Adjusted in PSE7.
Photographed in Theodore Roosevelt National Park, South Unit, Medora, North Dakota on 9-12-2009 at 7:53 p.m.