How to drink like a bat
This one just sticks out its tongue and throbs carry nectar to its mouth
Sorry, English language, but “tongue pump” or even “conveyor belt” may turn into a verb for drinking.
Some very patient biologists have observed tropical bats drinking nectar in a way never documented before. Finding a term for this feeding is a challenge.
“Odd” is what Mirjam Knörnschild called it when she saw an orange nectar-feeding bat (Lonchophylla robusta) extend its tongue to drink. The bat didn’t lick, lap, sip, slurp or even take its tongue out of the liquid. Along a deep groove on each side, edges undulated as if the tongue clenched in waves like the human intestine. Nectar just slid up the grooves. “It was like a conveyor belt,” says Knörnschild, now of Free University of Berlin.
Efficient tongues matter in the strenuous life of a nectar specialist. A 15-gram bat like the orange nectar-feeder needs to drink about 1.5 times its body weight each night, requiring roughly 800 to 1,000 flower visits. At any given flower, “two seconds would be a long visit,” Knörnschild says.
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Under such pressure, extreme tongues have evolved, and not just in the orange nectar-feeding bat. Some flower-bat tongues end in patches of hairlike protrusions that engorge with blood and extend outward into a nectar mop. And a bat in South America stretches out a tongue 1.5 times the length of the rest of its body, Knörnschild says. This whopper tongue doesn’t attach at the back of the mouth like typical mammal tongues but reaches down the throat to anchor between the sternum and the heart.
Orange nectar-feeders’ tongues aren’t as long but have great grooves. To see what free-flying bats do, colleagues Marco Tschapka and Tania Gonzalez-Terrazas of the University of Ulm spent long nights in Panama luring bats to hover in just the right position and babying a fussy high-speed camera not at all designed for jungles. “It sounds trivial, but it wasn’t,” Knörnschild says.
The bats drink with the tongue-in-place pumplike throbbing, the researchers report September 25 in Science Advances. The motion probably combines with the liquid-to-liquid attraction that also makes fluid rise in thin capillary tubes, the researchers suggest.
However it works, it’s probably more exciting than the drinking mechanics of more famous specialists. Vampire bats don’t actually suck blood, Knörnschild says: “They lick it like a cat would lap up milk.”
PUMP IT In this slow motion video footage, a hovering bat (Lonchophylla robusta) uses its grooved tongue to pump nectar up to its mouth, without breaking contact with the surface of the liquid.
Credit: M. Tschapka et al/ Science Advances 2015