Scientists think they know purpose of the cassowary's casque

February 18, 2019, 1:17 p.m.
A cassowary in profile
Photo: Keitma/Shutterstock

The southern cassowary and its distinctive casque, or fanlike helmet, have stumped scientists for 200 years. What on Earth is it for?

A flightless relative of ostriches and emus, the bird is native to Australia and Papua New Guinea. Its casque sets it apart from the rest of its family, leading to a great degree of speculation about its use. Is it for protecting the head while the bird runs through thick vegetation? Does it help with attracting mates? Or is it some sort of resonance chamber that amplifies its cry?

The answer seems to be none of the above, according to a study published in Scientific Reports.

The study, conducted by researchers at La Trobe University in Australia, suggests the casque is a radiator, or "thermal window," that helps keep the birds cool in their hot locales.

"Just as humans sweat and dogs pant in hot weather or following exercise, cassowaries offload heat from their casque in order to survive. The hotter the ambient temperature, the more heat they release," lead author Danielle Eastick says in a statement.

Eastick and her team used a handheld thermal-imaging device to scan the heads of 20 cassowaries in a variety of weather conditions. The images showed the casques releasing only a minimal amount of heat when the temperature was 41 degrees Fahrenheit (5 degrees Celsius), and a lot more heat when the thermometer hit 96 degrees Fahrenheit (36 Celsius).

Given its size — the southern cassowary can weight up to 130 pounds (59 kilograms) — and its black feathers, the creature would need a way to regulate its body temperature.

"Our results are quite compelling and it’s highly probable this is what the casque is actually used for," Eastick says. "It's really exciting to think we may have solved a mystery that has baffled scientists for so long."