They seem to have a kind of compass in their bodies: some types of animals can surprisingly direct themselves specifically on their long journeys. But where is this sixth sense? The results of an experimental study on now roaming bats indicate: In mammals with a magnetic sense, the fuzzy steering system is in the cornea of the eye.
Seeing, hearing, smelling, tasting, and feeling are standard – but some animals have an extra capacity for perception, as many studies have shown: Some species of birds, fish, turtles, and mammals such as dolphins, whales, or bats also have a guiding ability when moving over a large area, which seems to be It is not based on the classic five senses. It is now assumed that they are able to perceive magnetic fields and use them as a navigational aid. Experiments already indicate that this ability depends on iron oxide particles in specific cells of the body that act as “microscopic compass needles”. However, in the case of mammals with a sixth sense in particular, it is unclear where these vector cells might be located.
Where is the compass?
So far, there have only been indications that gray birds can perceive magnetic fields through sensory receptors in their parked eyes in order to find their way around their branching tunnel systems. As part of their study, researchers led by Oliver Lindyk of the Leibniz Institute for Animal and Wildlife Research in Berlin investigated the question of whether magnetic sense could also be in the eyes of mammals that migrate over a wide area. The focus has been on the indigenous European bats (Pipistrellus nathusii), which, like some bird species, migrate from their summer places in northern and eastern Europe to regions with a temperate winter climate.
For the study, scientists caught some rough-skinned bats at night on the coast of the Baltic Sea, which were on their late summer migration to the south. Some animals were given a drop of oxyproprocaine in the eye. It is a short-acting anesthetic that is used in human ophthalmology for both diagnostic and surgical procedures. It numbs the corneal nerves. However, eyesight is not affected, as the scientists also explained while studying the state of bats through experiments. This enabled them to rule out that the observed effects were due to poor eyesight, which bats sometimes use for guidance in addition to the echolocation system.
In one group of bats, the scientists treated both eyes, while in the second group, only the cornea of one eye was numbed. The bats acted as a control group and were given an inactive saline solution as eye drops. Then the researchers released the animals one by one into a field eleven kilometers from the hunting site. In doing so, they recorded the directions at which the animals flew away in the dark.
Derailed with eye drops
Found: Members of the control group and the group subjected to unilateral corneal anesthesia immediately headed south according to their migration route. But this was not the case with bats whose corneas were numbed on both sides: “These animals flew away in random directions,” Lindyk says. “This indicates that the numbing of the cornea permanently disrupted the sense of direction – and that apparently this also works well in one eye.” As the corneal anesthesia wears off rapidly, the animals sustained only temporary damage and they were soon able to start their journey again. To the south, scholars confirmed.
“For the first time in an experiment, we were able to observe how a migratory mammal was literally derailed – a milestone in the behavioral and sensory biology that allows us to research the mammalian biological navigation system in a more targeted way,” says Lindicky, Study A. Specifically, the results now provide clear indications that the sense of direction in migratory mammals is usually in the eyes. However, the sixth sense remains obscure, scientists finally confirm: how and where exactly is in the bat cornea, how it works, and whether it is indeed the suspected magnetic meaning should now be demonstrated in future studies.
Source: Leibniz Institute for Animal and Wildlife Research, Specialized article: Communication Biology. Doi: 10.1038 / s42003-021-02053-w