Ears tuned to water

Nov 02, 2010
Fig. 1 Drinking greater mouse-eared bat (Myotis myotis). Image: Dietmar Nill, MPI f. Ornithology

(PhysOrg.com) -- For bats any smooth, horizontal surface is water. Even so if vision, olfaction or touch tells them it is actually a metal, plastic or wooden plate. Bats therefore rely more on their ears than on any other sensory system. This is due to how smooth surfaces reflect the echolocation calls of bats: they act just like mirrors. In nature there are no other extended, smooth surfaces, so these mirror properties prove to be a reliable feature for recognition of water surfaces.

Scientists from the Max Planck Institute for Ornithology in Seewiesen investigated this phenomenon in 15 different species from three big bat families and found that all tried to drink from smooth plates. In addition they found that this acoustic recognition of is innate. (Published in Nature Communications November, 2nd 2010).

Water is important for to get a drink. However many species also use rivers, lakes or ponds for foraging as water insects are soft and easily digestible. In addition prey is easily detectable with as the acts like a mirror, reflecting the calls back almost completely. Only if there is an insect on the surface, it reflects back an echo.

In their study Stefan Greif and Björn Siemers from the Max Planck Institute for Ornithology simulated water surfaces in a large flight room and offered the bats a smooth and a structured plate each from either metal, wood or plastic. In weak red illumination the researchers observed whether the bats would fall for this trick and try to drink from the smooth plate. They could hardly believe what they saw: "The Schreiber’s bat tried to drink up to a hundred times in ten minutes from the smooth plate", says Stefan Greif. Three different species - the greater mouse-eared bat, the Daubenton’s bat and the greater horseshoe bat - showed the same results on all three materials. Only from the wooden plates some bats tried to drink a little less. To test how widespread this behaviour is, the scientists tested 11 additional species with one individual each on the metal plate - likewise with a positive result. At least with the insect eating bats this behaviour thus seems to be wide spread.

Fig. 2 A Schreiber’s bat (Miniopterus schreibersii), trying to drink from a smooth metal plate. Image: Stefan Greif, MPI f. Ornithology

The researchers were astonished that the animals did not learn that these artificial, acoustic mirrors are not water surfaces. They observed bats that accidentally landed on the smooth plate, took off again and after a few rounds flying resumed their drinking attempts. Even when the scientists placed the plate on a garden table, the bats flew partly underneath the table and then tried to drink, although this certainly is not a natural situation for a pond.

The association of a smooth, horizontal surface with water seems to be hardwired in the bat’s brain. Nevertheless, how do they process the contradictory information coming from other sensory systems? Only in the world of echolocation the metal plate corresponds to water, other sensory systems like vision, olfaction and touch surely tell the bat otherwise. The researchers repeated their experiment in darkness, thereby eliminating the input of vision. The result: the number of drinking attempts increased from 100 to 160 in ten minutes. "So it seems like the bats integrate and weigh up their sensory information, but echolocation dominates all the others", explains Stefan Greif.

Finally the scientists wanted to know if the acoustic information on water is fixed already in the animals’ genes. They repeated the experiment with juveniles who had never seen a lake or a river before. Flightless juveniles were captured in a cave together with their mothers and were raised until they were able to fly. These young bats likewise tried to drink on first contact in their life with a smooth surface. The behaviour therefore seems to be not learned but innate.

In nature, all smooth horizontal surfaces might be bodies of water, but what about all those man-made smooth surfaces like skylights, car roofs or winter gardens? If bats so persistently take horizontal mirrors for water, do they also try to drink from these artificial surfaces until exhausted? This question remains so far unanswered. "We think that bats in nature have other possibilities. They show high site fidelity and probably have their established water surfaces. Maybe they try new surfaces, but eventually they will move on", speculates Stefan Greif. Future studies are needed to evaluate the occurrence, extent and potential ecological consequences of such a scenario.

Explore further: Male monkey filmed caring for dying mate (w/ Video)

More information: Stefan Greif & Björn Siemers, Innate recognition of water bodies in echolocating bats, Nature Communications. Published online November 2nd, 2010

Related Stories

Keeping an ear out for kin

May 18, 2010

(PhysOrg.com) -- Bats can distinguish between the calls of their own and different species with their echolocation calls, report German scientists of the Max Planck Institute for Ornithology in Seewiesen. ...

Some bat numbers up in Britain

Dec 31, 2006

At least four species of bats in Britain have reversed decades of declining populations and have grown in numbers recently.

Bats recognize the individual voices of other bats

Jun 05, 2009

Bats can use the characteristics of other bats' voices to recognize each other, according to a study by researchers from the University of Tuebingen, Germany and the University of Applied Sciences in Konstanz, Germany. The ...

Recommended for you

Male monkey filmed caring for dying mate (w/ Video)

Apr 18, 2014

(Phys.org) —The incident was captured by Dr Bruna Bezerra and colleagues in the Atlantic Forest in the Northeast of Brazil.  Dr Bezerra is a Research Associate at the University of Bristol and a Professor ...

Orchid named after UC Riverside researcher

Apr 17, 2014

One day about eight years ago, Katia Silvera, a postdoctoral scholar at the University of California, Riverside, and her father were on a field trip in a mountainous area in central Panama when they stumbled ...

In sex-reversed cave insects, females have the penises

Apr 17, 2014

Researchers reporting in the Cell Press journal Current Biology on April 17 have discovered little-known cave insects with rather novel sex lives. The Brazilian insects, which represent four distinct but re ...

Fear of the cuckoo mafia

Apr 17, 2014

If a restaurant owner fails to pay the protection money demanded of him, he can expect his premises to be trashed. Warnings like these are seldom required, however, as fear of the consequences is enough to ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

BloodSpill
not rated yet Nov 02, 2010
It makes me wonder if there should be a master list of all innate human actions that should be drilled into people during school. How do I overcome my own limitations if I'm not aware of them?

More news stories

Biologists help solve fungi mysteries

(Phys.org) —A new genetic analysis revealing the previously unknown biodiversity and distribution of thousands of fungi in North America might also reveal a previously underappreciated contributor to climate ...

Researchers successfully clone adult human stem cells

(Phys.org) —An international team of researchers, led by Robert Lanza, of Advanced Cell Technology, has announced that they have performed the first successful cloning of adult human skin cells into stem ...

UAE reports 12 new cases of MERS

Health authorities in the United Arab Emirates have announced 12 new cases of infection by the MERS coronavirus, but insisted the patients would be cured within two weeks.