The head of cassowaries may be protected from impact as they traverse dense forest thanks to a foam-like 'helmet' with keratinized covering.
“A casque or helmet composed of a firm foamlike substance with a heavily keratinized covering is located on the top of the head. The purpose of the casque may be to protect the birds when moving head first through dense forest vegetation or may be a social display.” (Fowler and Miller 2003:99)
“We recently had an opportunity to dissect an adult male Cassowary found dead near Feluga, in northern Queensland, and found that the casque is neither horny nor bony. The skull does not have a protuberance as might be expected and the casque itself consists of a keratinous skin over a core of firm, cellular foam-like material that looks like some hi-tech plastic. This foam is very resilient and gives the casque elastic properties that appear to be lost in dried museum skins. The casque is very rigid longitudinally but can easily be squeezed and deformed laterally. When pressure is released the casque springs back to shape.
“The casque is usually described as serving to provide protection as the bird moves through thick vegetation. Cassowaries normally move slowly with head and neck erect, but when moving at high speed they stretch the neck out horizontally and run full tilt through the vegetation, brushing saplings aside and occasionally careering into small trees. The casque would help protect the skull from such collisions. There is also the possibility that it has a secondary sexual function. However, both sexes have one, the female’s being larger than the male’s and I (F.C.) have not seen it being particularly prominent in mating displays or fighting. We believe the foam inside the casque supports the idea that it acts as a protective device – it appears to have excellent shock-absorbing qualities.” (Crome and Moore 1988:123)
