" I have three different receptor-sensitivities in my eyes: red, green and blue. Hawks, like other birds, have four. This hawk can see colours I cannot, right into the ultraviolet spectrum. She can see polarised light, too, watch thermals of warm air rise, roil, and spill into clouds, and trace, too, the magnetic lines of force that stretch across the earth. The light falling into her deep black pupils is registered with such frightening precision that she can see with fierce clarity things I can’t possibly resolve from the generalised blur. "

― Helen Macdonald , H is for Hawk