Short-beaked echidnas of the semi-arid Dryandra Woodland in Western Australia face searing hot summers. They can’t pant like dogs to cool off since their long, thin, sticky tongues are useful only to feed. Neither do they sweat as we do. Nor do they lick their arms like kangaroos whose evaporating saliva cools the underlying blood vessels. Vultures squirt watery poop on their naked legs for the same reason. Since these hedgehog-lookalikes don’t have these options, how do they beat the heat?
They waddle about during the pleasanter times of day or night. Just as the thorns of cacti reduce heat loss, so do the two-inch-long spines of echidnas. When the quills are slicked back, they trap warmth. When they are raised, heat escapes. Another strategy of the domestic cat-sized animals is to lie flat, pressing their spineless stomachs to the cool soil with their legs and noses stretched out. “These areas have very little insulation and so they can dissipate body heat through them,” says Christine Cooper of Perth’s Curtin University, Australia. But these measures only go so far.
Resting inside logs
In studies conducted in the early 1900s, captive echidnas died when temperatures exceeded 35C. Yet, wild ones rested inside hollow logs where the air temperature can exceed 40C. Constrained by their enclosures, the captives didn’t have many options to remain cool. But an eagle-eyed student of Cooper’s observed some animals blowing bubbles of snot when exposing them to warm temperatures in the lab.
The pencil-thin, three-inch tubular snout is the egg-laying mammal’s prey detection kit. It is covered with electroreceptors that detect the underground wrigglings of ants, termites, and grubs. These sensors work only when they are moist. For this reason, the echidna’s nose has about 100 mucous secreting glands. Cooper wondered if the secret of surviving heat stress could lie in the wet snout.
She and her team drove around Dryandra at about 5 kmph for 12 hours a day. When they spotted an echidna, they pointed a thermal camera at it instead of catching the animal and taking its temperature. “Improvements in technology are letting us study animals in the field without disturbing them,” she says. “That’s one of the positives for wildlife conservation.”
With this method, they remotely assessed the surface temperature of nearly 125 short-beaked echidnas throughout the year. This kind of contactless work doesn’t disturb the animals, and it also made the researchers’ work easier. Frightened echidnas dig into the ground, gripping roots and rocks to anchor themselves and leaving only their spines exposed. While this thwarts predators, researchers can face the daunting task of excavating a stubborn, prickly mass.
Getting close
Despite Cooper’s hands-off approach, not all the animals were amenable to being study subjects. As her pickup truck approached, some dove into the nearest log or vanished behind a bush. Some young ones, however, ignored the researcher while she filmed them. “A few foraged right around my feet,” she says. “When I lay on the ground to take photographs from a good angle, they climbed on top of me. That’s always a neat experience when you are observing animals.”
All the hours of driving and lying motionless paid off. Viewed through a thermal camera, the echidna’s pointy nose appears blue, much cooler than the rest of its body, which glows in the warm colours of orange, pink and red. When a hot animal blows mucus balloons that burst over its nose, evaporation cools the blood vessels inside the snout. Circulating this blood through the body brings down the body temperature.
“We weren’t really surprised by the findings,” Cooper says. “We knew evaporation is a really important avenue for heat exchange.” Blowing snot bubbles might seem like juvenile behaviour in human society, but for short-beaked echidnas, it makes the difference between life and death.
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