Motoring2 mins ago
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Despite appearances, most birds do have good stereoscopic vision. Predatory birds, such as hawks and owls, have their eyes facing more forwards, and their binocular sector is bigger. In other birds it may be quite small -- and a few may even have some binocular vision behind them, as hares do. Some birds have binocular vision under their heads. This is most noticeable in the bittern (a type of heron), which often hides standing in the reeds with its beak pointing upwards. While doing this it can look forwards with both eyes at once. I'm not sure if birds have what some grazing animals have, which is two areas of good focus in their eyes. I think both cattle and horses have asymmetrically shaped eyes, and can simultaneously focus on the grass in front of them and the horizon around them -- good for spotting an approaching lion. It's certainly true that many birds use only one eye to get a clear look at a threat -- easy to see when a hen or a thrush turns its head to one side to watch you with one eye. I think it must be this which gives the impression they can't look forwards.