Animal of the week August 22, 2011 -- Funky monkey

Despite repeated promises to send more regular animals, I am red faced with embarrassment at my failure to do so, but it has been a busy summer and I've been rushing around exhausting myself till I am blue in the face -- but not as red and not a blue as the face of this week's (month's) animal of the week, Mandrillus sphinx (mandrill)

Mandrills are perhaps the most striking primates for several reasons. Not only are they they the largest monkeys, with the biggest males reaching a weight of 54 kg, they are also the primates with the greatest sexual dimorphism (difference in body size between the sexes) -- with females typically reaching just 14 kg -- just over a quarter the size of the largest males and half the size of the average male (although for extreme sexual dimorphism, see the green spoon worm). But what mandrills are best known for are their brightly coloured faces and bottoms.

Both the front and rear ends of mandrills are shaded with vivid blues and reds, the colours are brightest in the dominant breeding males. Mandrills are rather poorly understood creatures and the precise functions of the bright skin colours are unknown, though they no doubt help communicate since the intensity of colours increases not only with sexual dominance but also with agitation and excitement. Mandrills live in forests in Cameroon, Gabon, Equatorial Guinea and Congo (Brazzaville) where the bright colours and a scent gland on their chests might help communication in dense vegetation. Mandrill groups typically consist of up to 20 females and their offspring led by one dominant male, although several of these groups may frequently associate with each other in large gatherings called hordes -- some hordes may number over 1000 making them the largest gatherings of non-human primates.

Other primates with bright or noticeable rear ends include drills (the closest relatives of mandrills, which lack the brightly coloured faces), baboons, and chimpanzees -- baboons have large red backsides all the time to create a cushion for upright sitting and female chimpanzees to advertise fertility. Another primate with similarities between its arse and face (in terms of appearence and what comes out) is David Cameron.

Figure courtesy of Robert Young, wikimedia commons