By Victoria Gill
Science reporter, BBC News
Male great bustards show their white tail feathers in mating displays
Male great bustards have developed a trick to make their elaborate mating displays even more alluring to females, a study suggests.
The large birds lift and point their bottoms towards the Sun, say scientists, making their bright white tail feathers more conspicuous.
The behaviour makes them more visible to females, say the scientists.
The Behavioral Ecology and Sociobiology study suggests the birds actively use the Sun in their displays.
Pedro Olea, a scientist from the IE University School of Biology in Santa Cruz, Spain, led the study.
He and his colleagues observed the birds on mating grounds called leks.
"We recorded the orientation of more than 400 male displays in relation to the [position of the] Sun, and to females, at several leks in the plains of north western Spain," he explained.
At these sites, up to 200 males gathered to perform their courtship displays - lifting their tails and rotating their wings in order to display their white body feathers.
The researchers found that the male birds tended to direct their tail feathers towards the Sun, especially in the morning.
"The displays were more directed towards the Sun when it was most visible," the researchers wrote in their article.
Dr Tommaso Pizzari, an ornithologist from Oxford University, who was not involved in this study, said the findings were "very interesting".
The males orientate their displays to the Sun, especially in the mornings
"They raises the interesting possibility that the male birds use the Sun to their advantage - that they have learned to use variation in the environment," he told BBC News.
He added that it was important to study these reproductive displays, which represented "one of the biggest puzzles in evolutionary theory".
"These displays are costly for the males - they make them more conspicuous to predators and they have to keep their ornamental (feathers) in good nick," he said.
"But, especially when males display together, and females go to the leks to window shop, they're a huge advantage.
"That's why we think these puzzling traits evolved and are specific to males."