Compass orientation of a migratory bat species depends on sunset direction

April 04, 2019

Whether it is bats, wildebeest or whales, millions of mammals move over thousands of kilometres each year. How they navigate during migration remains remarkably understudied compared to birds or sea turtles, however. A team of scientists led by the Leibniz-IZW in Berlin now combined a mirror experiment simulating a different direction of the setting sun and a new test procedure to measure orientation behaviour in bats to understand the role of the sun's position in the animals' navigation system. The results demonstrate for the first time that a migratory mammal species uses the sunset direction to calibrate their compass system. Furthermore the experiment, which is published in Current Biology, indicates that this capacity is not inherited and first-time migrating young bats need to learn the importance of the solar disc at dusk for nightly orientation.

The experiment that scientists Oliver Lindecke and Christian Voigt from the Leibniz Institute for Zoo and Wildlife Research (Leibniz-IZW) designed and conducted together with colleagues from Latvia and the United Kingdom was based on two steps: First, several Soprano pipistrelle bats (Pipistrellus pygmaeus) were randomly assigned into two groups. At nightfall during their migration period, one group could watch the natural sunset at the Latvian Baltic Sea shore. The other group however watched the sun going down via a large mirror which was reversing the direction of the natural sunset exactly 180°. For the latter animals, the real sunset was blocked from vision by the taped sidewall of their holding cages. Later at night, animals of both groups were transported inland, away from the beach of the Baltic Sea, for the second step of the experiment: On a forest meadow, one bat after the other got released remotely from a specially designed circular release box. By the help of this box, the very direction an animal took when it left it, could be recorded. Prior studies showed that take-off orientations could be used as a proxy for departure flight orientation in these bats.

"The new orientation assay, the circular release box for bats, ruled out any visual influence at takeoff and allowed us to compare the directions bats of both groups where taking", explains Lindecke. "The results show two fundamental aspects in bat navigation: Firstly, the setting sun's direction plays a crucial role because there is a significant difference in the bats' orientation with the group which experienced the mirrored sunset departing in opposite direction compared to the control group. And secondly, only adult bats showed directional preferences", Lindecke summarizes the results. "Subadults displayed random orientation in both groups, which suggests to us that young bats need to learn long-distance navigation during migration from older conspecifics", concludes Christian Voigt, senior author and head of the Department of Evolutionary Ecology at the Leibniz-IZW. How this learning process works and which social factors and practices contribute to it remains unknown and needs further investigation.

Mammals remain remarkably understudied with regard to navigation during migration. One of the reasons I a lack of experimental assays that measure a correlate of migratory orientation such as those that exist in birds and sea turtles. The larger migratory mammals, for example wildebeest or whales, are challenging to handle for any experimental work. Bats could fill this void as they have emerged as an important study model in movement ecology. They combine high ecophysiological diversity with a variety of movement behaviours. Bat eyes evolved to sense a wide range of light and a broad spectrum of wavelengths. Presumably, insectivorous bats rely heavily on vision like fruitbats when orienting over long distances since echolocation and path integration are ineffective and error-prone at distances larger than a few dozen meters. The results of this study are the first empirical evidence for the specific cues and mechanisms a migratory mammal uses for navigation.
-end-


Forschungsverbund Berlin

Related Bats Articles from Brightsurf:

These masked singers are bats
Bats wear face masks, too. Bat researchers got lucky, observing wrinkle-faced bats in a lek, and copulating, for the first time.

Why do bats fly into walls?
Bats sometimes collide with large walls even though they detect these walls with their sonar system.

Vampire bats social distance when they get sick
A new paper in Behavioral Ecology finds that wild vampire bats that are sick spend less time near others from their community, which slows how quickly a disease will spread.

Why doesn't Ebola cause disease in bats, as it does in people?
A new study by researchers from The University of Texas Medical Branch at Galveston uncovered new information on why the Ebola virus can live within bats without causing them harm, while the same virus wreaks deadly havoc to people.

The genetic basis of bats' superpowers revealed
First six reference-quality bat genomes released and analysed

Bats offer clues to treating COVID-19
Bats carry many viruses, including COVID-19, without becoming ill. Biologists at the University of Rochester are studying the immune system of bats to find potential ways to ''mimic'' that system in humans.

A new social role for echolocation in bats that hunt together
To find prey in the dark, bats use echolocation. Some species, like Molossus molossus, may also search within hearing distance of their echolocating group members, sharing information about where food patches are located.

Coronaviruses and bats have been evolving together for millions of years
Scientists compared the different kinds of coronaviruses living in 36 bat species from the western Indian Ocean and nearby areas of Africa.

Bats depend on conspecifics when hunting above farmland
Common noctules -- one of the largest bat species native to Germany -- are searching for their fellows during their hunt for insects above farmland.

Tiny insects become 'visible' to bats when they swarm
Small insects that would normally be undetectable to bats using echolocation suddenly become detectable when they occur in large swarms.

Read More: Bats News and Bats Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.