Don’t worry: this isn’t Lewis Carroll’s maddeningly unanswered riddle “Why is a raven like a writing desk?” (Although, if you’re interested, it turns out that has been answered.) There is an answer to this one—two answers, in fact.
Answer 1: They both make sounds by vibrating strings.
Well, strings, feathers—they’re all the same, right? This Club-winged Manakin produces its courtship song by vibrating its wing feathers: they strike each other about 107 times per second.
Ferruginous Hawk. Photo by Nathan Rupert*
You don’t have to look at many birds to realize that they are very variable in appearance: hawks look different from hummingbirds, and both look different from peacocks. You can spend a lot of time looking at birds, though, before you realize that they are hiding a lot of variation inside their mouths: long tongues, short tongues, spiky tongues, curly tongues, forked tongues, frayed tongues, brush-like tongues.
Like bird bills, bird tongues are specialized to each particular bird’s way of feeding. Birds that feed on nectar have tongues specifically adapted to nectarivory, often with many little protrusions at the tip of the tongue, giving it a frayed or brush-like appearance. This brushiness increases the surface area of the tongue, making it better at picking up nectar.
Rainbow Lorikeet using its brush-like tongue to feed on flowers. Photo by Alan (Kaptain Kobold)*