One of the world's rarest primates and Africa's most endangered primate. It is a member of the Cercopithecidae (Old-world Monkeys)
family, closely related to the baboons and even more closely to the Mandrill.

The Drill is similar in appearance to the Mandrill, but lacks the colorful face. They are semi-terrestrial monkeys, exhibiting extreme
sexual dimorphism with males weighing on the average around 37 pounds but up to 100 lbs - three times the size of females.
I would guess that this is a juvenile male, as I had the opportunity to photograph an adult male at the Barcelona zoo
in 2009:

http://www.pbase.com/drjaysel/image/125141887

They are hunted everywhere as bushmeat, and it is not uncommon for an entire group to be shot as it takes refuge in the trees.
The population on the southern tip of Bioko is one of only three known remaining populations. There are currently
forty-six drills in zoos world wide, and two of them are now in the Detroit Zoo with lots of
open space to roam in.