Unlike panting, dilation of blood vessels in the beak to cool off conserves water in arid habitats
When temperatures are scorching, yellow-billed hornbills in southern Africa’s Kalahari Desert dilate blood vessels in their beaks to thermoregulate and cool themselves, according to a study published May 18, 2016 in the open-access journal PLOS ONE by Tanja van de Ven of the Percy FitzPatrick Institute of African Ornithology, University of Cape Town, South Africa, and colleagues.
While mammals have sweat glands to keep their bodies from overheating, birds can rely on panting (evaporative heat loss) and dilation of their blood vessels (non-evaporative heat loss), especially in their beaks. Toco Toucans are an example of this: their oversized beaks account for up to 60% of their non-evaporative heat loss at air temperatures above 28 degrees Celsius. Although not as extreme as toucan beaks, hornbill beaks are still quite large in relation to their bodies. To determine if hornbills might also use their beaks for this purpose, the authors of this study raised the air temperature around 18 wild-caught southern yellow-billed hornbills and tracked their heat loss using thermal imaging. .
The researchers found that beaks accounted for up to 20% of birds’ non-evaporative heat loss and suggest that the heat loss benefits of beaks in hot weather likely vary depending on where the birds live. In rainforests where toucans typically live, for example, beak heat loss could be key, as humidity can make panting less effective. For desert-dwelling southern yellow-billed hornbills, beak heat loss could be significant because, unlike panting, it can help conserve scarce water.
Tanja van de Ven notes: “We discovered that, like toucans, hornbills can use their beak as a controllable heat radiator. cooling.”
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