Beautiful plumage gives male ostrich the rule of the roost
THE BRIGHTER the feathers, the healthier the chicks.
That’s the finding of a Stellenbosch University study published in the journal Behavioural Ecology and Sociobiology last month linking the colour of a male ostrich’s feathers with the size and health of its offspring.
It comes down to immunity, explained Dr Maud Bonato, who has been studying the birds at a research farm in Oudtshoorn.
Mortality among ostrich chicks in their first three months of life is high – but also very varied, fluctuating between 10 and 50 percent.
So the team allowed ostrich females to choose males with different combinations of traits. They then compared the immune resistance of the parents to the immune resistance and growth of their chicks.
“The immune system is very important when a chick grows,” Bonato said. “They need energy to grow, but they also need energy to fight bacteria and disease.”
The key was in the colour of their plumage. In some bird species, like ostriches, a male’s bright feathers seem to indicate a stronger immune system.
“Having bright plumage comes at an energy cost, so only the fittest males can afford to have both a strong immune system and bright feathers,” explained coauthor Professor Michael Cherry.
A good quality male will have strong contrasts between his black and white feathers, which he shows off to the female while wooing her. And the research shows that this strength is passed on: bright white feathers on dad predicts a stronger immune response in the kids, while the coloration of both his feathers and his bill predict that they’ll have a high growth rate.
The results tie in with a 2009 paper in which Bonato also found that female ostriches laid bigger and better eggs when they mated with the more attractive bright males. This is called maternal investment.
It’s a double whammy: the male’s high immunity combined with the female’s increased maternal investment result in stronger, bigger chicks more likely to survive the first three months post-shell.