The Masai Giraffes, Giraffa camelopardalis tippelskirchi, sport the most irregular patches of any giraffe race. These males are having a casual sparring bout, after which they ambled off in opposite directions. More intense tests of strength involve head slamming. Males accumulate bone tissue on the skull so that with maturity the male's head becomes almost like a sledgehammer. A mature bull's head may weigh 15 pounds more than the head of a male half his age.