Toucan’s beak beats the heat
Published: 30 September 2010 (GMT+10)
This is the pre-publication version which was subsequently revised to appear in Creation 32(4):28–29.
Charles Darwin was intrigued by the toucan’s monstrous beak. (The toucan’s bill accounts for about one-third of its body length.) He wrote that “toucans may owe the enormous size of their beaks to sexual selection, for the sake of displaying the diversified and vivid stripes of colour with which these organs are ornamented.”1
In other words, Darwin suggested the big beaks attracted mates. Others have suggested the beaks are for peeling fruit, warning off territorial rivals, or are a visual warning to predators.
However, new research has identified a key function of the toucan’s bill is to help the toucan keep cool in tropical climates, or when expending a lot of energy while flying.2,3,4 Just as elephants flush their large ears with blood to let the heat dissipate into the air, and thus keep the core temperature of the body stable, so the toucan uses its massive beak to radiate heat away rapidly.5
The toucan’s beak meets the requirements for being a thermal radiator perfectly—dare we say, it “fits the bill”! Not only does it make up 30% to 50%6 of the toucan’s overall body surface area, the beak also has an extensive network of blood vessels close to the surface. And it is not simply a passive thermal radiator, as the heat exchange is carefully regulated.
Using infrared photography, which displays warm areas as bright and cool regions as dark, researchers observed that the toucan could adjust blood flow to its beak. In mild conditions (16º–25ºC), only the proximal region of the bill (i.e. nearest to the toucan’s head) was used to radiate heat. But with increasing air temperature, and/or when the toucan is expending energy as in flight, the distal part of the bill begins to receive increased blood flow, becoming warmer.
So, in hot conditions the researchers’ infrared thermography showed toucans’ beaks glowing with radiated heat as warm blood flooded them. In contrast, at cooler temperatures the bills would go dark as blood flow was cut back to a minimum.
The researchers assessed that heat loss from the adult toucan’s bill could account for as little as 25%7 to as much as 400% of resting heat production—the largest range so far observed in nature.
What’s more, toucans can even do it in their sleep! The researchers wrote, “We found that sleeping birds show transient changes in bill surface temperature without evidence of awakening, indicative of sleep-state transitions associated with changes in thermoregulatory state.”2
What would Darwin have made of all this? Could his ideas about natural selection have accounted for how the toucan’s bill could have become endowed with such a crucial and sophisticated function—with its separate blood vessel networks supplying the distal and proximal regions of the beak?
Tellingly, the researchers who identified the incredible heat exchange function of the toucan’s beak, although crediting the bill to evolution, shied away from the origins issue, saying that “the selective forces that led to the large bills of present-day toucans remain elusive”.2
Elusive indeed. Yet intelligent people today would recognize that the thermal radiators of modern motor vehicles with their thermostat-regulated rate of coolant flow to the radiator are the product of intelligent design. Consider how much more sophisticated is the toucan’s ability to control the flow of blood to its “thermal radiator” beak to achieve thermoregulation—a truly integrated system with complex feedback mechanisms.
The toucan is better viewed as evidence of a purposeful Creator who created things for a purpose, on purpose!
- Darwin, C, The Descent of Man: And Selection in relation to Sex, John Murray, London, 1871, Volume II, 1st edition, 1871, p. 227. (Accessed via: The Complete Work of Charles Darwin Online, <darwin-online.org.uk>). Return to text.
- Tattersall, G., Andrade, D., Abe, A., Heat exchange from the toucan bill reveals a controllable vascular thermal radiator, Science 325(5939):468–470, 2009. Return to text.
- Price, M., A bird with a big air-conditioning bill, ScienceNOW Daily News, <sciencenow.sciencemag.org/cgi/content/full/2009/723/2>, 23 July 2009. Return to text.
- Kaplan, M., Giant toucan bills help birds keep their cool, National Geographic News, <nationalgeographic.com/news/2009/07/090723-toucans-bills-radiators.html>, 23 July 2009. Return to text.
- All warm-blooded animals need to release excess body heat. Humans do it in part by sweating, dogs by panting. Return to text.
- Despite its dominating size, the beak comprises only about one-twentieth of the toucan’s bodyweight. Return to text.
- At cold temperatures, losing body heat through the bill could theoretically become a liability. But the researchers point out that toucans are well known for tucking their bills beneath their wings and orienting their tail feathers around the beak during sleep. This posture insulates the bill and mitigates heat loss incurred while asleep. Return to text.