The bird on the left is an "independent plumage" ruff. This species is particularly weird because they appear to have 5 genetic genders. The short version is: there are male and female ruffs. The ruff, Philomachus pugnax, has 3 different males: "Independents" "Satellites" "Faeders" Independents fight for territory on leks (mating grounds) which females typically like. Satellites "orbit" the lek without fighting and get occasionally allowed to mate with females by the independents. This is allowed because leks are only successful if there are multiple males for the females to choose from. Faeders "cross-dress" by having typically female plumage. Faeders then wait for an actual female to signal they are ready to mate and then a faeders swoops in and does the deed.
To make things even more interesting, these traits are caused by chromosomal inversions (part of a chromosome got "flipped" during meiosis (sex-cell replication)). If a faeder or satellite happens to mate with a female who is a carrier for the inverted chromosome. Their male offspring has a 50% chance of inheriting both of the inverted chromosomes from both parents which will cause death! ☠️
You can read more here: https://www.allaboutbirds.org/news/among-ruffs-some-fight-loving-fighters-dont-like-to-fight/ And here: https://learnthebirds.com/the-ruff-our-non-binary-migrant/
