Hornbills join toucans in the cool beak club

In the scorching heat of the Kalahari Desert, some birds still manage to keep their cool.

Thermal imaging reveals that the southern yellow-billed hornbill (Tockus leucomelas) vents heat from its beak, a phenomenon previously observed in toco toucans (Ramphastos toco). A team of South African researchers snapped infrared photos of 18 hornbills on a farm in the southern edge of the desert at temperatures from 15° to 45° Celsius.

When air temperatures hit 30.7° Celsius, the difference between beak surface temperature and air temperature spikes — indicating the birds were actively radiating heat through their beaks. At most, the birds lost about 25.1 watts per square meter through their beaks. Hornbills probably manage this cool trick by dilating the blood vessels to increase flow in their uninsulated beaks, the team writes May 18 in PLOS ONE.

Toucans lose about 60 percent of their total heat loss through their beaks, but hornbills only shed up to 20 percent of their heat loss through this method. The researchers chalk that difference up to larger beak-to-body-size in toucans.