The not-so-blue jays

摘要

HERE in New Hampshire, I live next to a wooded area, and covid-19 means that I have been spending a lot of time at home. This has translated into me becoming a bit of a birder. All day long, I text friends with my sightings - a hawk walking on the ground hunting smaller birds, a female northern cardinal, a bird that I thought was a woodpecker but was actually a warbler. I enjoy all of the birds I see, but my favourite visitors are the blue jays. They have such a beautiful pattern of bright blue, black and white, and they are fast movers too. Being the physicist that I am, I haven't just enjoyed the birds but have also been reading up on the science behind their colours. And here is the thing I learned: the blue jay's beautiful blue shades aren't real, they aren't blue like my jeans are blue. Not only is this shocking revelation true, but the blue jay isn't special either. It is common for "blue" bird feathers to appear to be blue, without actually having any blue colour in them. Reading this felt like saying that my hair isn't actually dark brown, it just looks that way. In fact, my hair looks the way it does thanks to melanin pigments, chemicals that absorb some parts of the light spectrum and reflect others.