Starlings aren't as common as they used to be but we've had quite a few in the garden during the present spell of cold weather. Today I noticed something odd about their eyes that I've never seen before. Above is a starling in wary mode, with its beady eyes looking all around for danger.
Here's a starling trying to feed with that rather strange technique that they use, with their beaks gaping then closing. Take a close look at where its eye is now - almost in its mouth and almost under the upper mandible.
When a starling switches from wary to feeding mode and it opens its beak wide the tension in the flesh on either side of the gape pulls the eyes forward, so that they are almost on the edge of the mouth and focused with binocular vision on the food source that it's pecking at. Imagine how their focus must flicker between near and far, and their field of view must vary between narrow and broad, every time they open and close their beak and their eyes move backwards and forwards accordingly.
For a human comparison, it would be somewhat akin to oscillating between reading from your computer screen with both eyes, and then focusing independently with each eye on the walls on either side of the room, then back to looking at the computer screen again, every second or so.