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Birds of prey constrained in the beak evolution race

Posted on 29 April 2016

New research by scientists at the Universities of York, Bristol, Sheffield and Madrid, reveals that eating different foods does not determine how birds of prey’s beaks evolve.

The skulls of a falconet and a vulture, the smallest and largest birds the team studied. Specimens located at the Smithsonian Institution National Museum of Natural History, Washington DC, USA (credit: Dr Jen Bright)

Birds’ beaks evolving characteristic shapes to eat different food is a classic example of evolution by natural selection.

However, research published in 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.

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.

Dr Jen Bright, Postdoctoral Researcher at the University of Sheffield and lead author of the study, 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”.

Professor Emily Rayfield, Professor of Palaeobiology at the University of Bristol and project lead, said: “Our research does not cast doubt on Darwin’s ideas, far from it. Instead it demonstrates how evolution has constrained raptor skulls to a particular range of shapes.”

Jesus Marugán-Lobón, of the Autonomous University of Madrid and co-author of the paper, said: “Basically, if you’re a bird of prey and you’re small, you look like a tiny falcon, and if you’re a bird of prey and you’re large, your skull looks like a vulture.”

The team are now keen to extend and test their ideas in other groups of birds.

Dr Sam Cobb, Senior Lecturer in Anatomyat the University of York and project lead, said: “Our results are important because they may help us identify one of the driving factors behind the outstanding diversity of bird species we see in the modern world.”

Further information:

  • ‘The shapes of bird beaks are highly controlled by nondietary factors’ by Jen A. Bright, Jesús Marugán-Lobón, Samuel N. Cobb and Emily J. Rayfield is published in Proceedings of the National Academy of Sciences.
  • The study was funded via a grant from the Biotechnology and Biological Sciences Research Council (BBSRC) to Professor Rayfield and Dr Cobb
  • For more information about the University of York’s Department of Biology, visit:

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