A classic example of evolution by natural selection is the way the beaks of bird species evolved into characteristic shapes to eat the different food in their habitat. However, new research from the Universities of Bristol, Sheffield, Madrid and York, published online on 28 April in the journal Proceedings of the National Academy of Sciences, found this does not apply to all species, and that raptors in particular have not enjoyed this evolutionary flexibility.
Lead author of the study, Dr Jen Bright, of the University of Sheffield, said: “Our results show that in birds of prey such as eagles and falcons, the shapes of the skulls change in a predictable way as species increase or decrease in size. The shape of the beak is linked to the shape of the skull, and these birds can’t change one without changing the other.
“We think that being able to break this constraint — letting the beak evolve independently from the braincase, may have been a key factor in enabling the rapid and explosive evolution of the thousands of species of songbirds such as Darwin’s finches and Hawaiian honeycreepers”.
The researchers used a method that allowed them to statistically quantify variation in the shape of predatory bird skulls and see how this shape variation compared with size, what the birds ate and how they are related to each other.
“Our research does not cast doubt on Darwin’s ideas, far from it,” said project lead Professor Emily Rayfield, of the University of Bristol. “Instead it demonstrates how evolution has constrained raptor skulls to a particular range of shapes.”
The research team is now keen to extend and test their ideas in other groups of birds.
(Source: University of Bristol press release, 29.04.2016)