It's in songbirds and in some type of songbird at that but I would not be surprised if, years from now, they discover that they all have it up to a point.
https://www.sciencedaily.com/releases/2 ... 090216.htm
PS The 'oil droplet' they mention is actually found in all species of birds but they are all different (in color and intensity of said color) depending on the needs of that particular species although they all, in one way or another enhance vision - sometimes deepening colors, sometimes filtering light. For example, sea birds have oil droplets that allow them to filter the glare from the sea water, allowing them to see the prey under the surface of the water. Birds are so cool!