Fig 1. Morphology of peafowl crests and crest feathers.

(A) A peahen (foreground) with the plane of her crest oriented towards the displaying peacock (background) as he performs train-rattling vibrations. (B) Both sexes have a crest with an inverted pendulum shape made up of between 20–31 feathers. This photo shows an adult male measured in vivo. (C) A single crest feather showing the pennaceous flag at the distal end. Note that only short, thin barbs are present on the relatively bare rachis (shaft) at the proximal end. (D) A whole crest sample mounted for the laboratory experiments. The two axes of vibrational motions (“in-plane” and “out-of-plane”) are indicated. (E) Mechanosensory filoplumes (circled) are located at the base of the peafowl crest feathers.