Giraffes' coats provide age clue
Male giraffes' age can be estimated by looking at the colour of their coats, according to research.
A 33-year study of male Thornicroft's giraffes in Zambia, Africa, has confirmed that the familiar pattern of brown blotches grows darker with age.
By comparing recorded colour changes, experts were able to generate a life-history profile for the animals.
They suggest the darkening patches could be associated with changes in testosterone at puberty.
Prof Fred Bercovitch from the Primate Research Institute and Wildlife Research Centre, Kyoto University, Japan, partnered with local naturalist Phil Berry, who has been documenting the animals since first becoming a park ranger in the 1970s.
"It's pretty amazing that he's simply written down tons of stuff for over three decades that we are now able to turn into scientific papers," said Prof Bercovitch.
The findings are published in the Journal of Zoology.
- Giraffes are world's tallest animals; born measuring 1.8m, males reach an average height of 5.3m
- They have horn-like bones on their head which males use when fighting rivals
- Their Latin name, Giraffa camelopardalis, means "camel marked like a leopard"
All species of giraffe are known to develop darker coats as they age but the exact timing of the changes were unknown.
"The main contribution of our work is that we could attach specific ages to coat colour changes, which provides something of a 'biomarker' of aging in giraffe," said Prof Bercovitch.
They found that males' coats first started to change colour at seven to eight years of age and brown blotches transformed to coal-black within two years.
"Given the timing of the darkening, my hunch is that it's linked to testosterone upsurges associated with puberty," said Prof Bercovitch.
Males of the species reach sexual maturity at approximately 10 years, leading Prof Bercovitch to suggest that the initial darkening phase indicates a "coming of age".
"I suspect that the blackening of the blotches is a public announcement to the other giraffe that a male is going through puberty; something like adolescent boys flexing their muscles to impress the opposite sex."
Thornicroft's giraffes are found solely in eastern Zambia's South Luangwa Valley and are one of the nine recognised sub-species of giraffe, each identified by different patterns in their coats.