Today I noticed a couple of crows in the grocery store parking lot — they both seemed to be looking at me — and I wondered if they’ve noticed the crow-beaks that humans are lately wearing and if they wonder why.
Though many passerines (perching birds, which includes most of the familiar songbirds as well as others with three toes facing forward and one toe facing backward) can see in the ultraviolet light spectrum, making their plumage look different (more varied) to them than it does to us, crows apparently are more violet visioned, like we are. (Caveat: not a lot of research has been done on crows’ vision.) The Corvid Research blog reported, in Dec. 2020 that
“A study of large-billed crows found them to be so weakly iridescent, that the authors proposed their violet-blues hues may simply be an artifact of chance, and play no functional role…. A 2007 study … confirmed that American crows, fish crows, and Chihuahuan ravens are sexually monochromatic from an avian visual perspective, meaning there’s no UV signaling of ‘male’ or ‘female’ hidden from us in their feathers. These birds were among only 14, of the 166 North American passerines sampled, for which this was true.”
“Despite these findings though, the role of UV in the lives of crows and other corvids hasn’t been rendered completely immaterial. When presented against high contrast backdrops (green foliage), fish crows are more adept at picking out UV reflecting berries than matte black Vaccinum berries. On the other hand, when both are presented in front of a backdrop that offers no contrasting advantage to the UV reflecting fruit (sandy backdrops) they pick out both berries equally. And while the UV spectrum may not be super useful to crows for coding information, that doesn’t mean the feathers of corvids don’t carry any weight. Common magpies, for example, convey all sorts of information from sex to age to territory status in their iridescent tail feathers.”
Black and other dark colours, whether we’re talking about a KN95 mask or a pair of long pants, absorb light, but that’s light in the human visible spectrum; black by definition is a “colour” that doesn’t reflect light in the visible range. Ultraviolet light is a wavelength of light that is just outside of the visible spectrum. There are actually materials that look black to humans but under UV light, observed with a UV camera, don’t look black at all. Maybe a KN95 mask is one of them, maybe not. (Lots more on the electromagnetic nature of light and how it relates to this question at, if you can believe this, Quora, written by Karl Brace, PhD, computer-aided design software engineer working at Intel.)
I would love to see colour as crows, hawks, owls, and songbirds do, just for a day or two, to really understand how the world looks to them.