Tim Birkhead

There are several ways we can know what a dog, a bird or, indeed, any other organism can see, for example either by looking at the structure of the eye and comparing it with other species, or by behavioural tests.

Compared with mammals, birds have relatively large eyes. In simple terms, a bigger eye means better vision, and excellent vision is essential for avoiding collisions in flight, or for capturing fast-moving or camouflaged prey. Birds' eyes, however, are deceptive - they are bigger than they look.