Bats suffer from big PR problems. They are traditionally associated with all kinds of bad things - from vampires and the devil, to rabies and COVID-19. And many people think they’re ugly too, though I think this Egyptian fruit bat is actually very cute.

But one thing is beyond doubt: bats are very clever.

Many of them fly by night and have astonishing powers of echolocation, while others are day-flyers that rely on their excellent eyesight. Some bats migrate over large distances. And they’re all very good at navigation.

A new study from Lee Harten et al. at Tel Aviv University sheds light on the Egyptian fruit bat’s impressive navigational skills - and in particular, whether they make use of a ‘cognitive map’.

As I explain in Incredible Journeys, the cognitive map has been the Holy Grail of animal navigation studies ever since it was first proposed back in the 1940s by the great Berkeley psychologist, Edward Tolman.

Because rats sometimes use shortcuts when searching for food rewards in mazes - entirely novel routes that they have never used before - Tolman thought they might be making use some of some kind of ‘cognitive map’ on which they stored information about the layout of their surroundings.

This was a very controversial idea because rats were then thought capable only of learning fixed routes based on trial-and-error (otherwise known as ‘stimulus-response’ or ‘S-R’ learning). Acquiring map-like knowledge couldn’t easily be explained in S-R terms, so it seemed impossible - according to the prevailing behaviourist orthodoxy.

Tolman was attacked on all sides and his opponents came up with all sorts of alternative explanations for the behaviour of the rats - some of which were pretty bizarre. But when cognitive neuroscience took off in the 1960s, it became possible to monitor what was going on in the brains of living experimental animals. And many discoveries made since the 1970s have born out Tolman’s hypothesis.

To cut a long and complicated story short, there’s now abundant evidence that various mammals - including rats, mice and human beings - have brain circuitry that allows them to form cognitive maps of their surroundings, though there’s still plenty of room for debate about how these work in practice.

What is less clear is whether any other animals have the same abilities, though there are some scientists who would make that claim - even for insects like honey bees.

Bats of course are mammals and it would be quite surprising if they were any less gifted navigationally than, say, rats or mice. After all, they navigate over much larger distances - and they are obliged to do so in three dimensions!

The new study is interesting because it provides pretty solid evidence for the first time that fruit bats really do use cognitive maps.

Using GPS trackers, Harten et al. mapped every single journey taken by 22 young bats (‘pups’) starting with their first excursion outside the nest and continuing every night thereafter for five months.

The pups gradually extended their home ranges until these reached a mean area of about 60 square km. Sometimes they undertook exploratory flights which took them beyond into unfamiliar territory. When they detected new sources of food, they would return to them later on to feed.

The striking finding was that the pups - like Tolman’s rats - often performed impressive shortcuts. These were defined as routes in which at least 50% of the animal’s journey was novel (i.e. the pup passed no closer th100m to any location it had previously visited).

You may wonder whether these shortcuts were just chance events. Well, they certainly looked intentional.

The paths the pups followed were almost as straight as their regular ‘commuting’ routes to familiar sources of food, and they were much straighter than their exploratory flights. Moreover, the pups headed straight for their targets right from the outset of these flights. Some of the lengthier shortcuts (described by the researchers as ‘long-cuts’) occurred at the end of exploratory flights. These sometimes involved navigating for many kilometers over unfamiliar territory.

And out of the 246 short- and long-cuts that were observed, hardly any was predictable on the basis of a randomised (‘random-walk’) movement strategy.

Could the pups have been following a scent trail?

There is plenty of evidence that homing pigeons make use of olfactory cues to find their way back to their roosts - especially when taken to distant and unfamiliar locations (though this is still the subject of some debate). But Harten et al. found no correlation between wind direction and navigational straightness. On this basis they judged it unlikely that the bats were relying on olfaction, though they could not rule it out completely.

What about echolocation then?

The researchers note that the bats’ echolocation system has quite a limited range - for example, they can detect a large tree only when it is within 50 m.

Harten et al. also found no evidence that the bats were making the kind of errors that would be expected if they were relying on ‘path integration’ or DR to make their shortcuts.

So they concluded that the bats must have been relying primarily on their acute vision to perform these navigational feats.

But of course good eyesight alone isn’t enough.

Harten et al. believe that, before setting off, the bats look around them and use the spatial arrangements of distant landmarks (such as high-rise buildings) to judge where they are and the heading they need to follow to reach their goal.

And since the bats are not following the same routes again and again, they must have some way of storing the different locations of these landmarks (as well as their varied appearances) in a form that doesn’t depend on any fixed point of view.

So, it really does look as if they must have some kind of cognitive map, though it will be interesting to see how other experts react to the new study.