This spectacular - and very beautiful series - is now available on Disney + and if you’re interested in animal journeys you’ll really want to watch it!
I was asked to help the production team at Plimsoll Productions and had fun trying to answer their questions about the navigational tools employed by a pretty diverse set of animals.
It was very nice to be given an on-screen credit as a ‘series consultant’!
[The following is the text of the annual EGR Taylor lecture which I delivered at the Royal Geographical Society in 2019.]
When we think of navigation, what typically springs to mind?
Maps and charts, compasses and sextants, and today of course the marvel of GPS. In other words, technical navigation.
But there’s another kind of navigation - which sometimes goes by the name of ‘wayfinding’. The ability of animals, large and small, human and non-human, to find their way without the help of any tools - apart from their senses and native wits. That’s what I’m going to be discussing tonight.
Let’s call it animal navigation.
Animal navigation is a big and complicated subject so I’m going to focus tonight on just one important aspect of it. How our fellow creatures make use of the light of the sun, moon and stars to find their way.
That animals - even ones as apparently simple as insects - can do such things, may come as surprise. But it should not. After all they face the same navigational problems as we do, and have access to the same sources of information. That they have found such good solutions is a tribute to the immense power of natural selection.
By the end of the evening I hope you will share my sense of wonder at the extraordinary abilities to which the evolutionary process has given birth.
But I want to start by saying a very few words about EGR Taylor - in whose memory I am delivering this lecture.
The first point to make is that, concealed behind those initials - EGR - was a woman. In fact Eva Taylor was one of the first women in the UK to storm the ramparts of what was then an exclusively male academy.
She was born in 1879 and took a degree in chemistry before shifting her attention to the study of geography. She never married, but raised two children during and after the first world war. She made ends meet by lecturing but rose eventually to become the first female professor of geography ever appointed in the UK - at Birkbeck in 1930. She retired in 1944 but continued working almost until her death in 1966.
Eva Taylor was, among other things, a leading expert on the history of marine navigation.
I first came across her work when researching my last book, Sextant, which is in part an account of how the longitude problem was finally cracked by the combined efforts of astronomers, mathematicians and instrument-makers in the mid-18th century. Please note: it was not the single- single-handed achievement of John Harrison!
Taylor’s classic study, poetically entitled The Haven-Finding Art, appeared in 1956 and, though long out of print, it’s a bible for anyone interested in the story of how human beings have solved the problems of navigating at sea. It’s also a very good read.
When I was writing Sextant I began thinking about the deep history of navigation. How did animals find their way around before human beings appeared on this planet?
I already knew a little bit about this from studying animal behaviour at university, but when I started to research the subject I quickly realised it had moved on a very long way.
I’ve spent the last three years writing a book that explores the fascinating science of animal navigation for a lay audience. Entitled Incredible Journeys it will be published by Hodder and Stoughton next April.
Although some profound mysteries remain to be solved, many amazing discoveries have been made in this field, and tonight I want to share just a few of them with you.
Of course we humans are animals too, so it makes sense to start by discussing how we used to navigate - before the advent of technology.
Civilisation is very new. The first villages and towns go back no more than 10,000 years or so. Navigational technology is newer still. The magnetic compass first appeared in Europe in the 12th century. The sextant and chronometer in the mid-18th, and GPS has been available for less than 30 years.
But people who looked just like us, and had brains as large as ours, have been around for about 300,000 years. So how did our species navigate for the first 290,000 years of its existence?
Like every other animal, our ancestors had to find food, water and shelter, and successfully reproduce. They had to keep track of each other and know how to find their way home. Their very lives depended on their navigational skills - whether by land or sea.
No other environment is as unforgiving as the open ocean. Yet somehow people managed to populate almost every habitable island on the surface of this planet long before histories began to be written - and all without the benefit of maps or instruments of any kind.
The most impressive amongst these early maritime explorers were the peoples of the Pacific islands. It is astonishing to think that sailors in wooden sailing canoes settled tens of thousands of islands scattered across the Pacific long, long before any European explorers appeared on the scene. Not only that - they also maintained regular contact between far-flung islands for hundreds of years. Voyages between the Hawaiian islands and Tahiti - an open sea distance of well over 4,000 kilometres - were once a fairly routine occurrence.
The navigational skills of the Pacific Islanders amazed European explorers like Bougainville and Cook when they arrived on the scene in the 1760s but they were unable to find out much about them. And those skills very nearly failed to survive the crushing impact of western colonial culture.
Luckily a few scholars in the 1960s and 70s - notably David Lewis and Thomas Gladwin - were able to track down a handful of surviving practitioners in the remote islands of Micronesia who generously shared their knowledge with them. The old skills had already disappeared throughout Polynesia.
The story old masters like Hipour had to tell was astonishing.
In the tropical waters of the Pacific, navigators can usually rely on clear skies by day and night. So the Micronesians made heavy use of the sun and stars to guide them on voyages that took them safely between tiny, low-lying islands often separated by hundreds of miles of open sea.
We all know that the sun rises in the east and sets in the west. What is true of the sun is also true of the stars. As the earth turns, both the sun and stars appear to move across the sky in slow, stately arcs.
Less well known is the fact that when the sun reaches its highest point in the sky it is either due north or due south of you. This is the moment we call noon.
And the same is true of every star. But unlike the sun, stars rise and set in the same place night after night.
The Micronesian navigators were an elite and their training began at a very early age. One of the most important things they learned was the precise and unchanging positions on the eastern horizon at which certain prominent stars rose during the night.
They also knew the corresponding positions on the western horizon at which these stars set. This knowledge gave them the basis of a perfectly reliable star compass.
Experience taught them which course to follow for each of the many islands they might need to visit. Setting out on a voyage from one island to another, they would set their course by reference to these stars.
The Micronesians also made use of one very valuable star . It tells you where true North lies – so long as you’re in the northern hemisphere. That star is of course Polaris.
Imagine the axis of the earth’s rotation extending out into space. It points directly towards Polaris. So if you’re standing on the north pole on a clear night Polaris is directly overhead. If on the other hand you’re on the equator, Polaris would just touch the northern horizon.
So as you move north or south the height of Polaris above the Northern horizon constantly changes. In fact it is a good measure of your latitude.
The Pacific navigators understood all this very well. By observing the height of Polaris they could work out roughly how far north or south they had traveled - though the system obviously broke down if they crossed the equator going south.
But the stars were of no value to ocean navigators during the day. Then they had to rely on the sun. Using the sun as the basis of a compass is a lot more complicated than using the stars.
Although it is roughly true that the sun rises in the east and sets in the west, the exact point on the horizon at which it rises and sets depends both on your latitude and on the time of year.
The Pacific navigators could calibrate their sun compass at twilight against the background of the stars.
But what were they to do during the rest of the day?
They could get an accurate north-south bearing at noon when the sun reached its highest point in the sky. But in order to steer a steady course at any other time they needed to make allowances for its gradual progress across the sky.
This may sound difficult, but it is a skill that can be learned - with sufficient practice. And the trainee Micronesian navigators had many years of that before they were recognised as masters! It is known as steering by ‘the shape of the sky’.
The Pacific islanders were not of course wholly reliant on their sun and star compasses, nor Polaris. They had many other remarkable skills at their disposal - notably the ability to read the wave patterns they encountered. They also made use of the behaviour of birds. But that is another story!
Having a compass of any kind is very helpful in setting and maintaining a steady course, as is the ability to determine your latitude. But in order to fix your position accurately out on the open ocean you also need a way of determining your longitude.
This was beyond the reach of traditional Pacific island navigators - as it was of European sailors until the 1750s.
Although the Pacific Islanders were no doubt exceptional, it’s a safe bet that most of our ancestors understood the basic principles of celestial navigation. That the sun rose in the east and set in the west, that noon was the moment when it reached the highest point in the sky - that Polaris marked true north, and so on.
How many modern city-dwelling humans know as much? Not long ago I encountered a police officer who was baffled when I referred to west-going traffic.
How much we have forgotten!
It doesn’t help that most of us are denied a clear view of the stars. Light pollution - that silent scourge - has effectively cut us off from the most sublime spectacle that nature can offer: the star- filled bowl of the night sky.
But I’m afraid the advent of GPS is a bigger threat. Of course it is a technical marvel and in many ways it makes our lives much easier and safer. But it is also turning us into navigational dunces and, worse still, it is encouraging us to turn our backs on the world around us.
Unlike every other animal, and unlike our own ancestors, we no longer have to open our eyes to find our way. We hardly even have to think. We are becoming entirely passive consumers of the navigational information effortlessly supplied to us by our little glowing screens.
As we lose the ability to navigate using our senses and wits, we are becoming more and more detached from nature and ignorant of our place in it. This is not - in my view - a healthy development.
...
So much for us humans. Let me turn now to how other animals navigate using the sun, moon and stars, starting with insects.
We have a much better grasp of how insects navigate than any other animals - apart from ourselves. What’s more, insects - for all their diminutive size and correspondingly tiny brains - are remarkably good at it.
They have of course had a head start over us humans - they have been around for hundreds of millions of years!
Among the best studied insect navigators are ants and bees.
One of the earliest serious students of ant behaviour was the polymathic British banker and politician, Sir John Lubbock, who kept colonies of ants at his country house just down the road from his friend Charles Darwin. Weekend visitors would be treated to a tour of these colonies.
In the 1870s he made a discovery that attracted little notice at the time. When testing how ants found their way back to their nest he noticed that the position of the lights he was using to illuminate his work had an effect on which way they headed. Though he was too cautious a scientist to make any large claims on the basis of this slender piece of evidence, Lubbock suspected that his ants might be using the position of the sun to help them set their homeward course.
Some years later, in the early 1900s, an eccentric Swiss doctor working among the native people in a remote corner of southern Tunisia began to take an interest in the local desert ants.
These remarkable animals live in a harsh and featureless environment and go on long foraging journeys, zigzagging around until they find some food to take back to their nest. Though the entrance of their nest is nothing more than a small hole in the ground and there are no landmarks to guide them, the ants can nevertheless head straight for it - even from quite long distances.
Santschi was fascinated by this behaviour and asked a simple question: how did they maintain such a straight course? It’s not clear whether he knew of Lubbock’s work, but Santshci wondered whether they were using the sun as a compass.
To test this hypothesis he conducted a simple but elegant experiment. First he hid the sun from the ants with a screen and then he presented them with its image from the opposite direction - reflected in a mirror. Sure enough, the ants altered course accordingly.
This was the first clear evidence that any non-human animal employed a sun compass. But because Santschi’s results were published in an obscure Swiss journal they passed without notice at the time.
Not much later, in 1919, the famous Austrian biologist Karl von Frisch made one of the most extraordinary discoveries in the history of the behavioural sciences.
Von Frisch was training honey bees to visit an artificial source of nectar (actually just sugar solution) and noticed that when it ran out they would periodically come back to see if the feeder had been replenished. That was intriguing but then he discovered something much more surprising.
As soon as the nectar supply was topped up and one bee from a hive had visited it, other bees from the same hive would quickly start to arrive in large numbers.
How did they know that it was now worth making the journey?
Von Frisch then noticed that the returning scouts - which he had marked with dots of paint when they were at the feeder - performed a curious dance on the vertical face of the honey comb, waggling their abdomens and running around in circles or figures of eight. The other bees excitedly turned towards them and touched them with their antennae. Then they all started heading off towards the feeder.
Von Frisch naturally thought the recruits must be following one of the scouts but that turned out not to be the case.
He then wondered if smell was they key. Perhaps the bees, alerted to the existence of a food supply, were locating its source by following some kind of scent trail.
So next he trained bees to feed from dishes on surfaces soaked with strong scents that would be picked up on their feet and bodies. Their fellow workers would be sure to detect these smells when these scouts returned to the hive.
The ‘recruited’ bees did indeed show a strong preference for feeders marked with these scents. So Von Frisch concluded that they located the new food supply simply by searching for the source of the scent on the dancer’s body.
That bees could alert each other to the existence of an attractive food source was surprising but this was just the beginning. Even more exciting discoveries were to follow.
In 1944, when von Frisch’s home and laboratory in Munich had been destroyed by Allied bombs he took refuge at his lakeside country estate, not far from Salzburg. During the course of that summer, he made a discovery that completely upset his previous ideas.
When scouts returned to their hive from a distant food supply that was marked with a particular scent, ‘recruits’ would often fly directly to it – even if that meant bypassing a much nearer feeder marked with exactly the same scent.
So it was clear that the recruits were not merely searching for any food source that smelt right: they were actively seeking out a distant source and ignoring one that was closer to home.
It appeared that the scouts’ dances conveyed information, not only about the existence of a food source, but also its bearing and distance from the hive!
The bees were in fact sharing precise navigational information with each other. This was truly astounding.
And that was not all. Later von Frisch discovered that the orientation of the waggle dance performed by bees returning from a feeding station gradually altered over the course of the day – in line with the changing position of the sun. The dance direction in fact reflected the relationship between the direction of the food source and the sun’s gradually altering position in the sky.
As Von Frisch himself said, the honey bee was the gift that kept on giving.
He next placed a bee hive in a hut and found that when sunlight was excluded from it, the returning scouts were completely disoriented. But if he showed them a flashlight, they would direct their dances as if it was actually the sun.
The bees could even orient their dances correctly when all they could see was a tiny circle of clear blue sky through a stove pipe installed in the roof of the hut.
When von Frisch discussed these baffling findings with physicist colleagues, they came up with a possible explanation. They suggested that the bees might be sensitive to the polarisation of sunlight.
Since we are unable to detect the polarisation of light with our unaided eyes this is a bit hard to explain. But let me have a go.
The light from the sun is composed of electric and magnetic waves that oscillate at right angles to the direction in which the light is travelling. These electric and magnetic oscillations radiate from the light wave at every possible angle - or plane of polarisation. Sunlight is therefore unpolarised.
But as sunlight passes through the atmosphere it is filtered by the air it encounters. The atmosphere mainly allows through light polarised in one particular plane. This results in the appearance of a strong pattern of polarisation in the sky above us. With the help of polarising filters, we can get a rough idea of what it looks like to animals that are sensitive to polarised light.
If you stand with your back to the sun on a cloudless day, wearing polarising sunglasses and look up at the sky overhead, you will see a dark-blue bar running left to right, from horizon to horizon. If you then turn slowly 90 degrees, either to the left or right, you can see the dark bar gradually lighten. That dark bar marks the region of highest polarisation, and its orientation in the sky is determined by the position of the sun.
Von Frisch realised that if the bees could see these patterns, they would not need to observe the sun itself: they would be able to infer its position from them. So a view of the sky through a stove pipe would perhaps be enough to enable them to orient themselves.
And this he was soon able to prove, with the help of polarising filters.
The discovery that honey bees could detect polarisation patterns in the sky, and steer by them when the sun itself was invisible, was a major breakthrough, but simply knowing the sun’s bearing does not enable animals to maintain a straight course – or at least not for very long.
Somehow - like the Pacific Islanders - they must compensate for the sun’s constant movement across the sky. And that means keeping track of time.
Was it possible that, on top of all their other amazing talents, honey bees might also have an in-built clock?
The short answer is ‘yes’. In the 1950s von Frisch conducted some very ingenious field experiments that demonstrated the ability of bees to make allowances for the movement of the sun during the course of the day.
This was the first demonstration of what is known as a ‘time-compensated’ sun compass in any animal - though a similar ability was discovered in birds at around the same time.
But it would be odd if bees were the only insects to have these abilities and soon they were found in other species.
A dedicated German scientist called Rüdiger Wehner has spent the last 50 years or so studying the desert ant. I was lucky enough to interview him in his apartment in Zurich.
Wehner first saw one of these ants in the Tunisian desert not far from where Santschi had studied them many years earlier. One of these long-legged insects was dashing around under the broiling sun in search of food and eventually seized the remains of a dead fly.
Like Santschi - of whose work he was then unaware - Wehner was amazed to see that it then ran straight back to its nest which was more than 100 metres away.
If honeybees had access to a sun compass based on polarised light it seemed likely that the ants (which are quite closely related) were using the same system, though nobody knew. And how such a system actually worked – even in bees – was still a mystery.
Wehner started tracking the ants across the baking sands using a cunningly contrived wheeled frame, which held a variety of different light filters above them as they ran around.
With its help, Wehner established that their homing abilities did indeed depend on their sensitivity to polarised light.
Back in the laboratory, using an electron microscope, Wehner located a patch of cells along the upper (dorsal) edge of the ant’s eye, which seemed perfectly designed to respond to light of this kind.
Wehner showed that this ‘dorsal rim area’ (DRA) was not only the key to the ant’s ability to detect polarised light, but also the basis of a time-compensated sun compass.
This discovery was a major breakthrough. Almost every insect since examined has turned out to have a system for detecting polarised light. The DRA is in fact the standard insect compass.
There is a great deal more to the desert ant navigation system than a time-compensated sun- compass but you’ll have to wait for my new book to find out more about that!
Let me now turn to another truly extraordinary insect - the best known butterfly in North America - the monarch.
These insects are astonishing migrants. They spend the winters clustered in vast numbers on trees in a tiny area of mountains in central Mexico - the location of which was only discovered by scientists in the 1970s.
When the days lengthen in the spring, the butterflies get sexually excited and rise up in vast numbers. After a mating frenzy, the females stream northwards and lay their eggs on milkweed plants in the southern US. They then die but their caterpillars hatch, feed and eventually a new
generation of adults emerges and heads further north, where the same process is renewed - again and again.
When heading north, the monarchs have a relatively straightforward navigational challenge. They need only find the milkweed plants and lay their eggs. But at the end of the summer, in response to the shortening days, the last brood of adult butterflies (the fourth or even fifth) heads south to Mexico. Some of them will be in Canada when they start out on their long trek. They may fly as much as 3,600 kilometres over a period of seventy-five days – roughly fifty kilometres a day.
But these butterflies have never made the journey before and there is no one to show them the way.
It is hard to imagine how such a feat is possible, but a series of remarkable discoveries over the last twenty years have given us many of the answers.
Drawing her inspiration from the earlier work of von Frisch and Wehner, Sandra Perez decided in the 1990s to find out whether the monarch, like the honey bee and desert ant, made use of a sun compass.
She kept a group of monarchs in a room, where the lights were turned on and off to simulate a day starting and finishing six hours later than the natural day - a process known as ‘clock-shifting’. In effect they persuaded the butterflies that the sun would rise six hours later than it actually did.
Perez and her energetic colleagues then released the butterflies one by one and estimated their preferred migratory heading with the help of hand-bearing compasses while running alongside them. They found that the clock-shifted butterflies generally headed in a west-north-westerly direction, while other butterflies that had not been clock-shifted followed the normal south-westerly course.
In other words the clock-shifted butterflies followed courses that would have made sense if the position of the sun itself had been shifted forward by six hours. This was exactly what was to be expected if the butterflies were using a sun compass.
Some years later, Henrik Mouritsen and his colleague Barrie Frost found a way of tethering the butterflies in a kind of flight simulator, which allowed them to monitor and record their heading accurately for as much as four hours at a time. This was much more accurate than Perez’s technique.
There was a notion that the monarch’s migratory abilities might not only involve a sun compass but also some way of determining their position.
To test this idea, Mouritsen and Frost tried physically displacing butterflies from one side of Canada to the other to see whether they would adjust their heading in response to the change in longitude.
It turns out there are limits even to the monarch’s navigational skills. They could not compensate for the displacement, so it looks as if they only have a compass.
Steve Reppert and his colleagues have since explored the physiological basis of the monarch’s navigational abilities. They have shown that the monarch responds not only to the position of the sun in the sky, but also, like the honeybee and desert ant, to light polarisation. It also has a clock built into its antennae.
This is already an extraordinarily complex and sophisticated system, but there may be yet another dimension to it. It is possible that the monarch is also a magnetic navigator. But again that is another story!
One last major puzzle remains. While the various mechanisms I have described may well enable the butterflies to get within a few hundred kilometres of their final destination, it is still unclear how they pinpoint their overwintering sites in the Mexican mountains.
One possibility is that in the closing stages of their journey, the butterflies home in on some kind of olfactory beacon, perhaps even the smell of the corpses of their dead brethren that cover the ground in their highland refuges.
The annual migration of the North American monarch is one of the most remarkable of all natural wonders, but it is one that future generations may never have the chance to witness. Not only are the forests in which the insects overwinter shrinking, as a result of illegal logging, but there are many other threats to the butterflies – including the profligate use of insecticides and herbicides that are either killing them directly, or destroying the food-plants on which they depend. So time may be running short for scientists to fill in the last piece of this extraordinary puzzle.
So far I have concentrated on how insects use the sun, but some of them are, of course, nocturnal. Take for example certain dung beetles - also known as scarabs.
Over the last twenty years, Eric Warrant and his colleague, Marie Dacke, have conducted a succession of fascinating experiments on nocturnal dung beetle navigation.
Dung beetles are in the recycling business and, but for them, we’d be buried in the stuff. Most of them consume the dung where they find it, but some species do something quite odd. They carve out a chunk, model it into a ball and roll it away as fast as they can - either to eat it themselves or lay their eggs in it.
Making a quick getaway from the dung heap is important because these beetles are very competitive. One beetle will rob another of its ball of dung if it gets half a chance. If the beetles fail to go straight they may well circle back and then get mugged.
For the ancient Egyptians these ball-rolling scarabs were a symbol of the god Khepri who rolled the ball of the sun across the sky, and images of scarabs feature frequently in their art. There’s a spectacularly large example in the BM, which though stylised is extremely accurate anatomically.
Warrant first heard about the ball-rolling scarabs at a conference in South Africa. The speaker said: It’s amazing, they just roll their balls in straight lines all the time and I don’t know how.
Warrant - who is an expert on insect vision - was sitting in the audience thinking excitedly, I know, I know: they must be using polarised light!
He and Marie Dacke later showed that just as bees and desert ants use the polarised light of the sun during the day, dung beetles rely - at least in part - on polarised moonlight!
This discovery caused a big stir, and was published in the leading scientific journal, Nature.
But Warrant and Dacke had a surprise in store. Some years later the two scientists were in camp on a brilliantly clear night at the edge of the Kalahari Desert. The velvet-black sky was filled with stars and they were waiting for the moon to rise, so that they could start a new experiment.
Then the beetles began flying in. To their astonishment they not only started making balls but also rolling them away in perfectly straight lines. But there was no moon!
Warrant and Dacke were really alarmed: perhaps they had got it all wrong.
But then a thought struck the two of them: there was a big bright stripe of light across the sky. The Milky Way! Could the beetles be using that?
To test this new idea, Warrant and Dacke started by attaching little cardboard hats to the beetles, to prevent them seeing the sky.
The insects then had much more trouble steering a straight course. But when transparent plastic hats were substituted for the cardboard ones, they managed perfectly well again, so it was plainly not the mere encumbrance of a hat that was putting them off their stride.
The beetles did indeed need to see the starry sky to maintain a straight course.
Warrant and Dacke next took the beetles to a planetarium where they could manipulate what they could see in the artificial sky projected above them.
It turned out that their ball-rolling performance was only a little worse when they could see the full starry sky, with the Milky Way, than when they could see the moon.
So it was plain that - in the absence of the moon - the beetles really were relying on the Milky Way to set their course.
‘This finding...provides the first documented use of the Milky Way for orientation in the animal kingdom.’ (Dacke.)
...
Let me now turn briefly to birds.
Migratory birds in particular face some formidable navigational challenges.
Arctic terns fly as much as 90,000 km in the course of a single year as they fly from one end the world to another, enjoying a permanent summer.
The bar tailed godwits that breed in Alaska can fly nonstop for a week or more as they traverse the entire Pacific Ocean on their way to New Zealand. 10,000 km flying without a break. By the time they arrive they will have lost a third of their body weight.
Closer to home the swallows that nest in England spend the winter in central Africa where they often roost not just in the same tree but on the very same branch year after year. Such a level of navigational accuracy matches that of GPS.
Sophisticated tracking devices can now tell us a great deal about where birds go and when, but finding out how they find their way much more difficult. 100 years and more of research has revealed that avian navigation is a very complicated business!
In the late 1950s, Franz Sauer had the bright idea of testing how indigo buntings reacted to the patterns of stars presented in a planetarium. He showed that they could make good use of them but it was the American scientist Stephen Emlen who worked out exactly how they did so.
Emlen invented a device to determine which way migratory birds want to fly. In essence it is a funnel-shaped cage with an ink-pad at its base and paper lining the sides. It is called - guess what? - an Emlen funnel.
Migratory birds get very restless when changes in the day length tell them it is time to travel. If you place them in cage they try to escape in their preferred migratory direction. Since their feet are inky they leave marks on the sides of the funnel that show which way they want to go. Not very sophisticated but quite effective.
Using this device Emlen was able to confirm Sauer’s findings - and added much more detail.
He showed that migratory buntings do not pay attention to individual star but rather rely on their ability to detect the rotational pattern of stars that marks the position of true north.
Perhaps surprisingly the exact arrangement of stars does not bother them. Emlen showed that if the birds are shown a night sky that rotates around Betelgeuse – a bright star in the constellation Orion – rather than Polaris, they are completely unfazed and set their course accordingly.
Such a system makes good sense because Polaris has not always occupied the position in the sky that it has today. So the only reliable cue in the long-term is not an individual star but the rotational pattern itself.
Many other birds that migrate by night find true north in the same way. The great advantage of such a system is that, once learned, it is simple to use and, unlike the sun compass, requires no form of time-compensation.
But one mystery remains. It is still not clear how birds learn to recognise these patterns in the night sky. It is hard to believe that they can perceive the rotational movement of the stars, as it is so slow, but they may be able to infer it by comparing ‘snapshots’ of the sky at intervals during the night.
Finally there is one major puzzle to which we don’t yet have a clear answer.
It seems that some migratory birds can tell when they have been shifted east or west. In other words they seem to have solved the longitude problem!
Kaspar Thorup displaced white-crowned sparrows on migration from one side of the US to the other...the adults adjusted, but juveniles didn’t. But how is that possible? Thorup could not explain it.
A very recent series of studies suggest that migratory reed warblers too can detect a large east-west displacement.
Russian scientists working on the Baltic coast have shown that adult reed warblers transported to a point near Moscow while migrating in a north-westerly direction can compensate for the shift.
What is more the birds can do so even when they are not physically moved, but are simply exposed to an altered magnetic field that matches a location hundreds of miles to the east or west.
It has long been known that birds have a magnetic compass sense. But a compass can’t tell you where you are, so something else must be going on.
It looks as if these warblers may make use a combination of celestial and magnetic cues to determine where they are ... but that’s another story!
...
We humans think we’re pretty wonderful, don’t we? Looking at the world through the lens of our own special interests it is easy to convince ourselves that we are superior to every other species on the planet.
What other animal can match our genius? We have the most amazingly elaborate languages, we make and build the extraordinary things, we can plan for the future and seem to dominate the planet. And of course that view has received powerful religious endorsement.
After all, what did God tell Adam and Eve?
‘Be fruitful, and multiply, and replenish the earth, and subdue it: and have dominion over the fish of the sea, and over the fowl of the air, and over every living thing that moveth upon the earth.’
Darwin of course put the cat among the pigeons and since then it has become clear that almost every skill once regarded as uniquely human is shared by some other animal.
No longer can we claim to be the only tool users, or the only animals that use language, the only animals capable of recognising themselves in a mirror... the list goes on and on!
And the old behaviourist belief that animals don’t think but merely respond automatically to reward and punishment has long since been demolished. Plenty of other animals can think, have feelings, make plans, and communicate complex ideas. Now we also know that even the smallest of them can navigate with extraordinary skill.
The only thing that really sets us apart is our ability to change the face of the planet - for better or for worse. And it is all too clear which way things are going. The almost infinitely complex web of life to which we belong - and on which we depend - is in now grave danger.
What I take from my study of animal navigation is a heightened awareness of the astonishing natural wonders that surround us, and a growing sense of alarm about what the future holds. Our own fate and that of our world now lies in our own hands - how can we possibly stand by and let the planet burn? There is no time to be wasted. We must take steps to protect the world we inhabit and the extraordinary creatures with which we share it - and we must do so NOW.
End
I recently enjoyed giving an online talk for students at the University of Kentucky. You might find it interesting if you want a very quick introduction to this fascinating subject!
Eurasian Reed warbler
There is plenty of evidence that ‘experienced’ migratory birds (ones that have already made at least one migratory round trip) can cope with massive geographical displacements. They can, for example, successfully complete their journeys, even after being ‘kidnapped’ by scientists and taken to places that are totally unfamiliar - which may be thousands of kilometers away from their normal route.
This is a really astonishing feat. In the same circumstances we humans would be completely at a loss but for our maps, sextants and compasses - or nowadays, GPS.
Some experts believe that these birds are ‘true’ navigators, capable both of determining their present position and of selecting the right course to follow to reach their goal. I’m not so sure.
Well, how do they do perform this feat? It looks increasingly likely that their ability to ‘read’ the characteristics of the surrounding geomagnetic field is the key (though exactly how this sense actually works remains uncertain).
In my book, Incredible Journeys/Supernavigators I mentioned some intriguing evidence that reed warblers might be using changes in magnetic declination (the angular difference between the directions of true north and magnetic north) to estimate their longitude. Such a skill would help them compensate for large scale east/west displacements from their normal migratory routes, though it would not enable them to determine their position.
A fascinating new study from Dmitry Kishkinev and his colleagues now casts doubt on this hypothesis, but it sheds new light on the role that magnetoreception plays in avian navigation.
Kishkinev et al. have now shown that experienced Eurasian reed warblers exposed to altered magnetic fields (characteristic of completely different and unfamiliar locations far from their normal migratory routes) can successfully reorient themselves. However, they can do so only when all three components of the geomagnetic field (declination, inclination and intensity) are present and match a real place - not when declination alone is altered (as in the earlier experiment).
The crucial thing about the latest experiment (like earlier ones from the same team) is that the birds were not physically moved. The changes to which the birds were subjected related only to the surrounding magnetic field. All the other cues available to them (whether based on sight, sound, or smell etc.) remained unaltered.*
One possibility is that these birds have access to some kind of ‘cognitive map’ based on gradients in the three magnetic parameters. (Claims for such ‘maps’ are, I have found, seldom justified by the evidence presented though they make good headlines!)
Such a ‘map’ would presumably be based on the birds’ experience of how the magnetic field varies along their migratory route. Such a map might extend beyond the confines of their standard journey if - and this is a very big if - the birds could somehow infer their new position by extrapolating the spatial variation of the various magnetic cues from those they have observed along their normal migratory corridor.
There are plenty of experts who doubt whether that is even theoretically possible, and it is unlikely that birds could generate positional information from the geomagnetic field that is anything other than very coarse-grained.
However, as the authors of the new paper rightly point out, there is no need to postulate such an extravagant navigational system.
Rather than using their mysterious magnetic map to ‘fix’ their position and set a course to their destination, there is a much simpler and more plausible explanation.
Perhaps the detection of magnetic fields that differ markedly from those they are familiar with warns birds that they are off course. The size and nature of these differences may additionally tell them in which direction they have been displaced. They might then be able to make course adjustments that return them to the correct migratory corridor. Once they are back on track, they should have a good chance of reaching their destination.
A set of skills like that would certainly be very valuable as a way of dealing, for example, with the effects of strong cross-winds. Whether, as the authors seem to imply, it counts as ‘true navigation’ is debatable.
The authors also cautiously observe that their findings do not support ‘a strong role for other environmental cues’ in the navigational tool-kit of the reed warbler.
It will be very interesting to see whether their results can be replicated in other bird species.
*What the researchers actually observe is the direction in which the caged birds attempt to fly under the altered magnetic fields generated by the coil systems that surround them. This technique is widely believed to be a good proxy for actually tracking where the birds go, though some experts question whether it is reliable.
Many navigators are worried about the consequences of our increasing reliance on automatic navigation systems - especially the ‘turn-by-turn’ apps based on GPS that are now embedded in every cell phone and every vehicle.
There’s plenty of evidence (which I discuss in Incredible Journeys/Supernavigators) that the passive use of these apps impedes the development of the mental maps that enable us to find our way around most efficiently.
There are even those who think that we may endanger our overall cognitive health by using them too much. And there’s no doubt that these apps impoverish our lives by discouraging us from taking an active interest in the world around us.
But nobody seriously thinks we can turn the clock back. Navigational apps are here to stay because they make life so much easier - and sometimes (though not always) safer.
The question is whether they can be tweaked so as to reduce or eliminate some of their drawbacks.
An interesting new study (Clemenson, G.D., Maselli, A., Fiannaca, A.J. et al. Rethinking GPS navigation: creating cognitive maps through auditory clues. Sci Rep 11, 7764 (2021). https://doi.org/10.1038/s41598-021-87148-4) examines the virtues of a different kind of app - one that does seem to help people develop a better grasp of the layout of their surroundings.
Instead of relying on the usual turn-by-turn directions, some participants in the new study followed a virtual, auditory compass (based on the Soundscape app - originally designed for visually-impaired users) in order to locate various goals dotted around the Microsoft campus. The compass indicated the straight-line route to each goal, and the user then had to navigate actively around any obstacles (like buildings) that stood in the way.
The authors acknowledge that the sample size was small, but they insist that - in contrast to a standard turn-by-turn app - the Soundscape virtual compass helped participants who were new to the campus develop a better sense of its geography.
They argue that “using auditory beacons to navigate can lead to greater explorative behavior and the formation of more accurate mental maps of the surrounding environment when compared to turn-by-turn navigation. Thus, demonstrating that it is possible to use GPS technology and promote learning through active navigation.”
They conclude that an auditory beacon is “a sensory augmentation that helps us create a stronger connection with our environment.”
This is a promising development, and I hope we’ll soon see more research of this kind. But I wonder whether the mass market navigational platforms will take heed of the new findings - and whether users are ready to embrace a more active approach to navigation than they have got used to. We’ll have to wait and see.
The latest edition of The New Yorker magazine (5 April 2021) carries an excellent article by Kathryn Schultz. It’s a review of the science of animal navigation based on her careful reading of several recent books on the subject, including my own Supernavigators. As you might expect from a Pulitzer Prize-winning writer, it’s lucid and elegant - and well worth a read.
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.
Charles Darwin was one of the first scientists to speculate about how sea turtles navigate on the open ocean. It’s a fascinating question and two whole chapters of Incredible Journeys are devoted to it.
One of the experts I interviewed was Paolo Luschi whom I visited at the University of Pisa. Paolo has spent many years doing experiments on turtles in the field, and he warned me to be sceptical of claims that these animals - remarkable though they are - are brilliant navigators.
A fascinating new piece of research reinforces his point.
Graeme Hays and his colleagues (including Paolo) tracked 33 green turtles migrating from their nesting beaches on the remote Indian Ocean island of Diego Garcia to their habitual feeding grounds dotted around the western part of that vast expanse of sea. The turtles travelled anything from a few tens of kilometers to more than 4,000.
Several interesting things emerge from the analysis of their data.
Firstly, the animals very seldom went directly to their destination - sometimes they massively overshot and they often strayed wildly off track. Nevertheless, they were still able eventually to locate their targets.
Secondly, the turtles were mostly swimming in such deep water that they had no chance of seeing the seafloor beneath them (they don’t normally dive deeper than 50m). In these circumstances it would be hard for them to make use of underwater topography to guide them. However, when they got close to their destinations and entered shallower water, they were able to head fairly directly towards them. This suggests that they were making use of ‘landmark’ information - possibly acquired on previous trips.
This study also compared what the real turtles did with what they might have done based two different assumptions about how they navigate.
The first, stringent assumption was that the turtles are true ‘map and compass’ navigators - able, that is, both to work out where they currently are and where they need to go to reach their goal.
The second, much simpler one was that the turtles only had access to a compass of some kind that would enable them to maintain a steady course. This would of course give them no positional information.
When the actual tracks followed by the turtles were compared with the ‘virtual tracks’ that emerged from the simulations, it became clear that the turtles were not perfect map and compass navigators. They lacked ‘the ability to always locate small isolated targets with pinpoint accuracy’.
But, since they were still able to find their targets, it looks as if the turtles must have access to some kind of ‘map’, though plainly not a very detailed or precise one.
Such a map is very likely to involve geomagnetic cues, though other factors might also be involved. (Ken Lohmann’s studies of captive loggerhead turtle hatchlings have already shown their acute sensitivity to geomagnetic information - see Incredible Journeys chapter 22 for a summary.)
It’s also clear that the turtles don’t rely on following a single, fixed compass course. This makes very good sense as such a crude mechanism would make them vulnerable to the disturbing effects of ocean currents that deflected them from their proper course..
The researchers found no evidence that, in the final stages of their journeys, turtles were making use of olfactory information - either smells in the air or tastes in the water - carried to them from their target. This is quite surprising, especially as hints of such an ability have emerged from earlier research.
This new study illustrates an important principle. Evolution doesn’t favour the emergence of perfect systems of navigation (or anything else), when merely adequate ones will enable animals to survive and reproduce successfully.
Good enough is good enough!
Lots of people who are interested in traditional methods of navigation - myself included - have long suspected that habitual GPS use weakens our ability to find our way around without the help of those little glowing screens.
As I observe in Incredible Journeys, using GPS relieves us of the need to pay attention to our surroundings and keep track of our position as we travel around. So it’s reasonable to suppose that people who rely most heavily on GPS will have more difficulty navigating without its help than those who keep their wits about them and their eyes open.
Now a new study has confirmed these suspicions.
There are two basic ways of navigating a new environment and they rely on quite different parts of the brain.
One is the ‘spatial memory strategy’. This means learning the relative positions of a series of landmarks and it allows us to form a ‘cognitive map’ of our surroundings. It depends heavily on a region in the middle of the brain called the hippocampus - which is crucial to our ability to recall events.
The other approach is based simply on learning a sequence of manoeuvres - turn left at the end of the street, then go 50 yards and then turn right, and so. Known as ‘stimulus-response learning’, it involves a different part of the brain called the caudate nucleus - which is also the key to learned skills like riding a bicycle.
Louisa Dahmani and Véronique Bohbot wanted to find out whether individuals who were dependent on GPS relied more on stimulus-response strategies than on spatial memory when they had to find their way without its help.
So they asked 50 healthy young adults (18 women and 32 men) between the ages of 19 and 35 who lived in Montreal, Canada, to perform a series of navigation tasks in computer-based ‘virtual’ mazes. The subjects also completed questionnaires that explored - among other things - how confident they were in their navigational abilities and the degree to which they relied on GPS in their every day lives. 13 of the original subjects took part in a follow-up study three years later designed to find out what the long-term effects of GPS use might be.
As expected, Dahmani and Bohbot found that the more people relied on GPS to navigate, the less likely they were to deploy a spatial memory-based strategy when they had to navigate without its help.
The follow-up study also suggested that there was a causal relationship between GPS habits and poor spatial memory. And it looks as if this relationship is ‘dose-dependent’ - in other words, the more you use GPS, the weaker your spatial memory is likely to become.
There is of course the possibility that people rely on GPS more and more because their spatial memory is declining. But Dahmani and Bohbot found no relationship between GPS usage and subjective reports of a weakening sense of direction. So this explanation seems implausible.
Higher GPS dependence was specifically associated with a reduced ability to remember and make use of landmarks. This probably explains why the heavy GPS users had more trouble forming cognitive maps than the other subjects.
The authors speculate that increased dependence on stimulus-response learning (based in the caudate nucleus) may actually weaken spatial memory (based in the hippocampus).
Dahmani and Bohbot refer to other studies that compare GPS use with the employment of other, more traditional aids like maps. These plausibly suggest that our level of engagement is an important factor in spatial learning.
GPS of course requires far less mental effort than following a route with the help of landmarks, or navigating with a map and compass.
The authors reach a simple conclusion: ‘the greater the use of GPS, the greater [the] decline in spatial memory over time’.
This has important implications for all of us, but especially for those - like the Inuit hunters of Arctic Canada - who have traditionally relied on their senses and wits to navigate perilous environments. Over-reliance on GPS in places where the direct route between two points may be unsafe (it might for example take you over a precipice!) can cost you your life.
Dahmani and Bohbot end with an interesting suggestion: perhaps GPS manufacturers could include landmarks in the automatic guidance instructions ‘as a way to re-engage users with their surroundings’. That might help, but we also need to put our gadgets aside whenever possible and exercise our little grey cells!
Here’s a link to a fascinating recent piece of research that explores the homing abilities of hunting dogs with a very well-developed sense of smell - so-called ‘scent hounds’.
Katerina Benediktova and her colleagues put ‘action cams’ and GPS-tracking collars on 27 hunting dogs and let them roam freely around a forest. (NB: the dogs were not passively moved to a new location like the animals in the earlier experiments we’ve considered.) They then analysed how the dogs found their way back to their owners - across no fewer than 622 trials at 62 locations.
(Even if you don’t want to get into all the details, it’s worth watching this video clip - it’s really fun!)
The team predicted that the dogs would either follow their own scent trail back to their owner (‘tracking’) or they would take shortcuts - a strategy they called ‘scouting’.
And that’s exactly what they found.
In 399 cases (almost 60%) the dogs used a simple tracking strategy to retrace their outward route. But in 223 cases (33%) they homed by a novel route. Somehow they ‘scouted’ out a completely new path that would take them back to their owners more quickly and directly.
How did they do that?
The research team have pretty well ruled out the possibility that the dogs made use either of the sun or polarisation patterns in the sky to help them set a course. They also believe that the wind direction would in most cases have made it very difficult for the dogs to ‘scout’ their way back to their owners using only their acute sense of smell.
But they did discover something quite new.
The ‘scouting’ dogs typically performed a short north/south run just before setting off for home - a so-called ‘compass run’.
Benediktova and her team think that these ‘compass runs’ reflect the dogs’ ability to detect the Earth’s magnetic field. They suggest that the runs may help the dogs’ recalibrate their DR (or ‘path integration’ system). In other words, they may help the dogs eliminate errors that have accumulated in their estimates of their position relative to their starting points. So perhaps their homing system is based on DR.
While this might explain how the hunting dogs in this experiment homed successfully, it’s hard to see how the dogs in the earlier experiments could have used DR to find their way home after being passively displaced. How would a dog in a closed basket accurately keep track of its position after a circuitous journey to a location 89 km away?
While it now looks more likely than ever that a magnetic compass plays an important part in the amazing homing abilities of dogs, I wonder whether they also make use of some kind of ‘cognitive map’ that works in conjunction with their DR, olfactory and compass skills.
More research is needed to tease out these issues.
No doubt there’ll soon be more to say on this subject. I’ll try to keep you posted!
Last time I talked about Colonel Richardson’s work with ‘messenger dogs’ in World War I.
A fascinating feature of Richardson’s work was his discovery that all dogs were not equally adept at homing. Drawing again on Michael Nahm’s review article, I now want to share with you the work of two later researchers. As we’ll see, their discoveries amplify the very same point - but still leave us with a big mystery.
The first, Bastian Schmid, worked in the 1930s. He was apparently the first scientist to address directly the question of how dogs find their way home.
Schmid’s experiments involved only three dogs that were displaced to an unfamiliar location at a straight-line distance of some 4-5 km from their home. Two of them succeeded in finding their way back (one was tested in the middle of the city of Munich, the other in a rural area). The dog released in the city homed over a distance of 4.5 km despite the presence of ‘street canyons’ that completely blocked the view. The third however failed completely on three occasions, even when he could have seen a familiar location.
Most intriguing was Schmid’s observation that the successful dogs “didn’t seem to use their noses”. They didn’t sniff for cues either close to the ground or in the air. “After an initial phase of orientation”, they simply trotted in a homeward direction “with raised heads”.
In the 1950s/60s, a researcher called Bernhard Müller carried out a much more elaborate series of experiments in Switzerland and Nepal involving no fewer than 75 dogs, both male and female. For some reason, Müller’s work seems not to have received the attention it deserves.
This is how Nahm summarises Müller’s approach:
“The ideal test series for a single dog consisted of four runs from the same release site at a distance of 2.5 to 3.0 km from the home territory, four runs from a different release site at 5 to 7 km distance and shifted clockwise through an approximate angle of 120°, and four runs from a distance of 10 to 89 km, shifted another 120°. Hence, a complete test series consisted of 12 runs that started at three different locations”
The dogs were carried to the release sites in closed baskets, usually via a series of complicated detours, and in all weathers (including snow and fog), both by day and night.
Just pause for a moment to consider: some of these tests involved homing from distances of 89 km. Could any dogs pass such a stringent test?
Well, the answer is yes!
Of the 75, no fewer than 19 completed the whole series of tests successfully.
Seven others did well at first but failed to complete the whole series successfully. 49 failed the first test and were then dropped.
Prior to the tests, Müller “determined the dogs’ social status by a number of selected behaviour characterics” and assigned them to three groups: dominant alpha-males, submissive omegas, and an intermediate group. He assumed that with increasing rank the ‘value’ of the home territory for the dogs would be raised. This in turn would, he predicted, result in a stronger homing impulse and greater success.
This proved to be the case. All 22 alpha dogs belonged to the group of 26 that either completed all the trials successfully or that started out well. The remaining four were high in the intermediate group.
None of the omega dogs returned home successfully. They just sought out humans or other dogs and then stayed with them. They showed no homing impulse at all.
The alpha dogs behaved very differently.
They would first spend a period of time near the opened basket (Müller called this the “adaptation phase”), and then left the release site, heading for home:
“On their way, they would avoid any contact with people. A very characteristic bearing of a dog on its way home … was to hold its head high and in a peculiarly stiff manner when trotting, its eyes appearing somewhat ‘veiled’. Often…they would stumble when the soil was uneven, or even collide with low wire fences”.
Müller noted that in general, “orientation by vision seemed to play a negligible role in their journeys”. And when they reached the same decision points on repeated tests (such as a ridge or pass), they would take different and typically shorter routes thereafter. It looked as if the dogs had “learned how to choose the correct direction in a general sense, and were able to adjust their routes accordingly”.
Müller was baffled by these findings, as well he might have been. He recognised that even if the dogs had access to some kind of compass, that would not explain how they determined their geographical position at the point of release - or how they could then select the right homeward compass bearing.
So we’re back to the same question: do (certain) dogs have access to some kind of cognitive map on which they can fix their position when displaced to an unfamiliar site - and on which they can also plot a course home?
This is a crucial question that arises in relation to many animals notably homing pigeons and migratory birds - like the cuckoos I discussed in an earlier post.
More of this soon!
