Throughout human history, we have depended on technology to help us navigate large distances. However, many animals possess an innate ability to navigate without any technological assistance; they seem to have a mysterious sixth sense. Some species, such as migrating birds, travel thousands of miles and return to the same nesting sites year after year. But how do they manage to do this?
Research on Nathusius Pipistrelle (Pipistrellus nathusii) has revealed that this mysterious sixth sense is linked to their eyes. Welcome to Wildlife In Focus. In this video, we take a closer look at Nathusius Pipistrelle and explore the evolution of their remarkable sixth sense.
Firstly, what do we mean by a sixth sense? Numerous migratory mammals—such as bats, whales, turtles, and birds—can sense the Earth’s magnetic field to navigate, and the Nathusius Pipistrelle is one of them.
Nathusius Pipistrelle
The Nathusius pipistrelle is a small, sleek, insect-eating bat with short, dense fur. Its fur is typically warm brown to reddish-brown on the back, while the underside is lighter, often appearing as light grey-brown. The face, ears, and flight membranes are dark brown to blackish. The bat has short ears with rounded tips, and the tragus—the small projection inside the ear—is blunt. Its wings are long and narrow in proportion to its body, which allows for fast, direct flight over long distances.
Habitat
The Nathusius pipistrelle can be found in a variety of environments, including mixed woodlands, riparian zones, wetlands, parklands, and suburban gardens. This species prefers habitats near water, which support abundant insect populations. It roosts in tree holes, beneath loose bark, in bat boxes, and occasionally in buildings.
One notable aspect of the Nathusius pipistrelle is its status as one of Europe’s few long-distance migratory bats. Some populations travel over 2,000 kilometers between their summer breeding areas in northern and eastern Europe and their wintering grounds in southern and western Europe. Migration typically occurs in the spring (heading north) and autumn (heading south).
Experiment
Researchers studied Nathusius Pipistrelle during their migration. They applied an anesthetic drop (oxybuprocaine) to the corneas of either both eyes, one eye, or a saline solution (as a control) before releasing each bat 11 km inland. Observers were unaware of which bat belonged to which treatment group.
What Happened
In the experiment, bats in both the control group and the one-eyed anaesthetized group flew south, as anticipated. However, the bats with both corneas anaesthetised flew in random directions. To determine whether vision was a contributing factor, scientists conducted light maze tests to confirm that the anaesthetic did not affect the bats’ eyesight.
The results of this experiment revealed that corneal sensing, not just vision, is crucial for orientation—having one functional eye is sufficient for navigation1.
What This Suggests
This strongly suggests that the magnetic sense in mammals may be located in the cornea rather than deep in the brain. The cornea is known to be one of the densest areas of nerve tissue in mammals, making it well-suited for detecting magnetic or directional cues.
Until now, the organ responsible for magnetic navigation in mammals was unknown. This study provides the first in vivo evidence that free-flying migratory mammals evolved a corneal sense for orientation.
Still a Mystery
What exactly is being sensed? Is it magnetite particles or light-sensitive cryptochrome proteins, like those found in birds? The precise mechanism remains unknown and is a subject for future research.
Broader Implications
However, the discovery opens new possibilities: it suggests that many mammals—including migrating whales, dolphins, and even mole-rats—may depend on corneal-based navigation. Scientists now have a specific target for identifying the receptor tissue.
References
- Lindecke, O., Holland, R.A., Pētersons, G. et al. Corneal sensitivity is required for orientation in free-flying migratory bats. Commun Biol 4, 522 (2021). [Accessed 13/08/2025]
