Living birds evolved from a flightless ancestor. The changes that eventually made flight possible not only involved modifying the theropod dinosaur body plan and evolving feathers, but also required the brain and senses to be developed to cope with life off the ground. To fly, a bird needs detailed feedback about its position in the air from its organs of balance, and also from visual information. The processing of these signals mostly occurs in a region of the brain called the flocculus, which is easy to see on a bird brain because it projects like a finger from the sides of the cerebellum. The flocculus varies greatly in size between species and, because of its function in balance, this size variation may relate to certain kinds of flying behaviour. The variation might also relate to the habitat in which a species lives, because flying in enclosed environments such as forests requires different flying skills to flying over open ground. Modern X-ray micro-CT techniques now allow us to see inside the skull of both living and fossil birds, revealing how the brain of modern birds has evolved. Using CT analysis, the size of the flocculus can be determined in dinosaurs and living and extinct birds, because its shape - and that of the brain as a whole - is impressed on the inner surface of the skull. The likelihood that flocculus size relates to flying ability has led some palaeontologists to infer flying ability for early birds such as Archaeopteryx from this structure. However, the relationship between flocculus size and flying behaviour has never been tested. It might be that the dimensions of the bony pocket that houses the flocculus are an overestimate of its size because other tissues lie between the flocculus and the bone. It might also be that the size of the flocculus is related to the overall size of the bird rather than to its flying ability or habitat preference. This project intends to test these possibilities by CT scanning the skulls of nearly 100 living species, and creating 'virtual brain models' from the internal space that housed the brain in life. The volume of the flocculus in each 'virtual brain' will be measured and analysed statistically to find out if flocculus size can be used to predict flying behaviour and/or habitat, or whether the size of the bird is the controlling factor. If strong relationships are not found we will know that palaeontologists should avoid speculating on the flying ability of extinct species based on flocculus size. Alternatively, if relationships are found, our test will have provided palaeontologists with a tool to test current ideas about the evolution of avian flight, and the transition from dinosaurs to birds.