Orientation and Habitat recognition

Like many animals, bats and shrews show homing abilities when released away from home. However, the means by which they orient are mostly unknown. One important mechanism is the usage of landmarks, i.e. visual, acoustic or olfactory cues along the way. Recent findings suggest that bats might be able to perceive the magnetic field of the earth and use it for orientation purposes. In cooperation with Dr. Richard Holland (then MPI for Ornithology, Radolfzell, now Queen's University, Belfast), we tested the homing response of wild Greater mouse-eared bats (Myotis myotis) after they had been exposed to an altered magnetic field at and after sunset. Magnetic manipulation at sunset resulted in a counterclockwise shift in orientation, consistent with sunset calibration of the magnetic field. However, magnetic manipulation after sunset resulted in no change in orientation. This indicates the importance of the
sun as an absolute geographical reference (Holland et al. 2010).

In bats, the echolocation of insect prey is well-studied, in opposition to their classification of extended surfaces as different habitat types. We were specifically interested in how bats recognize water surfaces by echolocation, whether it is possible at all, whether it is a learned behaviour and under which conditions they apply it to find water for foraging, drinking or simply as a landmark for orientation. We conducted the experiments on wild bats of 15 different species, funded by the Human Frontiers Science Program in a flight room. The results showed that bats perceive any extended, echoacoustically smooth surface to be water and tried to drink from it, even if other senses (like touch or vision) told them differently. Even hand-raised juvenile bats that had never before encountered a water body spontaneously tried to drink from smooth surfaces. This is evidence for innate water recognition through echoacoustic cues (Greif & Siemers 2010).

<p>_{Home, sweet home}</p>

The Bicolored Shrew (Crocidura leucodon) explores its new home for the first time, including the food bowl (top right corner) where it eats a few mealworms.

In order to investigate the function of shrews' twitters, the calls of common shrews (Sorex araneus) and greater white-toothed shrews (Crocidura russula) were recorded when the animals were exploring an unknown environment in the dark, the ground covered in hay. Experimental manipulation of the substrate's density affected the shrews’ call rate, which indicates an orientation function of the calls. Testing their echo power, we ensonified bricks with the twitters via a loudspeaker lying on the substrate at varying distances. The recorded echoes showed that the shrews' calls are indeed suitable to detect obstacles that are out of reach of tactile senses (Siemers et al. 2009).

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