The southern cassowary's hornbill helps keep the bird cool on hot days. Photo by La Trobe University
Feb. 14 (UPI) -- For 200 years, scientists have been trying to figure out the purpose of the helmet-like hornbill that protrudes from the top of the southern cassowary's head.
Thanks to new research out of La Trobe University, the mystery of the casque is solved.
Scientists determined the casque works as a "thermal window." The hornbill funnels and expels excess body heat, helping the iconic Australian species keep cool during summer heat.
"Our results are quite compelling and it's highly probable this is what the casque is actually used for," ecologist Danielle Eastick said in a news release. "It's really exciting to think we may have solved a mystery that has baffled scientists for so long."
For the study, Eastick used a thermal imaging device to observe the casques of 20 captive cassowaries. When the weather was cooler, the images showed only small amounts of heat were measured in the casques. When the weather heated up, larger concentrations of thermal energy registered in the casques.
Native to northern Queensland and Papua New Guinea, the southern cassowary, Casuarius casuarius, is used to warm weather. But the large, dark-feathered bird is also vulnerable to overheating. The casque helps the cassowary stay cool during summertime heatwaves.
Just last month, Australia set a new record for nighttime high -- 96.6 degrees Fahrenheit -- and research suggests extreme heat threatens a variety of species Down Under.
"Just as humans sweat and dogs pant in hot weather or following exercise, cassowaries offload heat from their casque in order to survive," Eastick said. "The hotter the ambient temperature, the more heat they release."
Researchers published their analysis of cassowary casques in the journal Scientific Reports.
If the "thermal window" explanation is accurate, the cassowary's casques could offer new insights into the physiology of dinosaurs.
"Many dinosaurs also had casques, so it's possible they too helped keep cool this way," Eastick said.