Instead Of Lapping It Up, Bat Tongues Pump Nectar Into Their Mouths

The pumping tongue nectar-feeding bat Lonchophylla robusta visiting a bromeliad flower. M. Tschapka/University of Ulm
Janet Fang 28 Sep 2015, 16:12

When certain bats drink nectar from flowers, they’re not siphoning it out or lapping it up. Their tongues have grooves and a pumping mechanism – a way of drinking that’s never been seen in any mammals before. According to a new Science Advances study, their tongues never separate from the nectar, and the sugary treat is sent into the bats’ mouths like a conveyor belt. 

Nectar is easily available and openly provided by flowers, which advertise this sweet, energy-rich resource in hopes of receiving pollination services in return. While insects that depend on nectar as their primary food source have specialized mouthparts, most nectar-feeding mammals and birds possess tongue modifications. Bats such as Pallas’ long-tongued bats (Glossophaga soricina) have long, hair-like papillae on their long, protrusible tongues. But there are a few bats that sport a completely different tongue – one that lacks long papillae, but has deep grooves (or canals) that run along the entire length of the muscly organ. 

To see how the grooved-tongued, orange nectar bat (Lonchophylla robusta) drinks, a University of Ulm trio led by Marco Tschapka used high-speed cameras to record 10 individuals feasting on honey water from test tubes resembling flowers. They also recorded eight Pallas’ long-tongued bats. Both species drink while hovering mid-air over the artificial flowers, typically for less than a second. But their nectar uptake techniques were very different, though they were similarly efficient at extracting the honey water.

After inserting its snout into the feeder opening, G. soricina would dip its tongue into the nectar, retract it into its mouth, and repeat up to seven times per visit. In contrast to these lapping movements, the grooved tongue of L. robusta stays in place the entire time with the tip submerged under the surface of the liquid: The grooved tongue uses pump-like muscles to transport the nectar up – and against gravity – into the bat’s mouth. 

The team doesn’t know exactly how the bats are doing this yet. Future work is needed to better understand the fluid dynamics and the interactions between the tongue and capillary action. You can check out some slow-motion tongue action in the video below.

 

 

Image in text: Lonchophylla robusta visiting the Malvaceae Quararibea cordata. M. Tschapka/University of Ulm
Video credit: AAAS/Carla Schaffer

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