Greater mouse-eared bat
July 24, 2014

Polarized Light Helps The Greater Mouse-Eared Bat Navigate

Rayshell Clapper for - Your Universe Online

The manner in which bats use echolocation has long been of interest to scientists, but new research shows that bats use more than echolocation to get around. In fact, the Natural Environment Research Council (NERC) recently announced a new discovery about the greater mouse-eared bat and how it navigates.

The greater mouse-eared bat uses “polarization patterns in the sky to navigate…The bats use the way the Sun's light is scattered in the atmosphere at sunset to calibrate their internal magnetic compass, which helps them to fly in the right direction,” according to a study published in Nature Communications.

The pattern of light polarization is the way light vibrates in one direction. In other words, sunlight scatters in the sky to create polarized light patterns. Studies show that these are mostly invisible to the human eye although with some training and know-how on what to look for humans can perceive polarization. However, science currently does not show a purpose for polarization patterns for human use.

According to National Geographic's Katie Langin, the study co-authors, Dr. Richard Holland and Stefan Greif of Queen’s University Belfast and colleagues from Tel Aviv University, took 70 female greater mouse-eared bats in Bulgaria. “The team placed each bat in a box that simulated polarized light at sunset. Some bats saw the natural pattern; others saw a band of polarization that was rotated 90 degrees…Next, they displaced the radio-tagged bats more than 14 miles (20 kilometers) from their roosting cave and tracked their movements in the night.”

What the researchers found was the bats with the altered polarization pattern of 90 degrees “went in directions that were rotated 90 degrees from the correct orientation.” However, the bats that were placed in the box with the correct simulated polarization found their way home.

This shows that bats use the same compass calibration method as birds. These greater mouse-eared bats are the first mammal known to use polarization patterns in the sky to calibrate and navigate. Bats use more than just polarization patterns. They also use the position of the Sun or stars, Earth’s magnetic field, smell, sight, and echolocation to navigate. But this study shows that they calibrate their navigation based on the polarization patterns.

The fact that bats use echolocation – a method of determining location by measuring the time it takes for an echo to return from something to the sender – is intensely interesting. Understanding this has helped scientists to protect the bat as well as to apply echolocation to the human world. Obviously, understanding the way in which bats use polarization patterns will help in future research.

Bat species have been experiencing declining numbers for several reasons. One such reason is wind turbines, which give bats the bends, as we call it in the human world. This leads to the bats running into or otherwise being hit by the turbines. In fact, NERC identified that this affects 300,000 bats each year in Europe. People will just find dead bats at the base of wind turbines. Migratory bat species are particularly prone to this issue.

Additionally, North American bats have suffered from the white nose syndrome, a deadly fungus decimating the North American bat population. As reported in January, since winter 2006-07 hundreds of thousands of millions of bats have died due to this epidemic.

Understanding how bats do what they do is important because they play necessary roles in world. Most important to human communities is that bats are natural pest controllers. According to the NERC, bats save humans millions in pesticide costs by eating insects. Obviously, this also saves people from any sort of pesticide poisoning or issues otherwise. For this reason, protecting bats has become particularly important.