15.How do dogs find their way home?

Dogs seem to have a built-in magnetic compass…

14.How birds steer by the stars - again, this time with the help of a globe!

If you found the explanation I gave in my last post a bit hard to follow - and I certainly wouldn’t blame you if you did - I hope this may make things a bit clearer. Do let me know either way!

13.How birds steer by the light of the stars...

Polaris (aka the Pole Star) stands in the sky vertically above the North Pole (not quite exactly, but near enough). That means that if you were at the North Pole during the long Arctic night and looked directly overhead you’d see Polaris. And if you were anywhere else in the northern hemisphere, facing towards Polaris, you would be looking due north (true, not magnetic). Though, as I explain in the video, thanks to the phenomenon of ‘precession’, this would not always have been the case, nor will it be in the not-too-distant future.

If you know where true north is, you can set a course in any direction. No wonder Polaris used to be called ‘Stella Maris’ - or the ‘star of the sea’. In the Middle Ages, the same term (which can also be translated as ‘the star of Mary’) was applied to the Virgin Mary, whose sky-blue cloak is emblazoned with a star in many medieval paintings. Mary was likened by the theologian Alexander Neckham (1157-1217) to the Pole Star, standing at ‘the fixed hinge of the turning sky’ by which the sailor at night directs his course. As I wrote in SEXTANT, ‘Polaris must have seemed a perfect symbol for the Mother of God, the immaculate spiritual guide and intercessor’.

https://upload.wikimedia.org/wikipedia/commons/5/5a/Star_Trails_Shoreline.jpg

But, as I explain in this video, birds are not human and they don’t use Polaris. Instead, they wisely attend to the rotational pattern of stars around it - something on which they can always count. To illustrate this, here’s a long-exposure photograph of the northern sky in which you can see the circular paths traced by each star. Polaris itself appears as a stationary dot at the centre of the pattern. The same principle would also work in the Southern Hemisphere, which is handy because there is no southern equivalent of Polaris: the southern celestial pole lies in a rather blank patch of sky, at least for the present!

12.The amazing journey of the blackpoll warbler...

Here is the first of what, if I have the energy, will be a series of short videos introducing some fascinating aspects of animal navigation. It relates to a tiny American bird: the blackpoll warbler.

These birds normally only weigh about 12 g and even when they fatten themselves up for their long migratory journey they only put on another 5 g. I think you’ll be as amazed as I was to discover what they can do.

The original research on which this story is based can be found here: DeLuca, W. V., Woodworth, B. K., Rimmer, C. C., Marra, P. P., Taylor, P. D., McFarland, K. P., ... & Norris, D. R. (2015). Transoceanic migration by a 12 g songbird. Biology letters, 11(4), 20141045.

11.Francis Chichester learns to navigate...

Sir Francis Chichester (1901-1972), best known today for his solo single-handed voyage around the world in the yacht Gipsy Moth IV, first learned to navigate in the air. In fact, he was a pioneering aviator (the first to fly solo across the Tasman Sea from east to west) and he only took to sailing towards the end of his career.

Chichester was to become an expert navigator, but, like the rest of us, he had to learn. Here’s his entertaining account of how, in 1929, he flew a Gipsy Moth aircraft from Liverpool to North Devon, not long after he had acquired his solo license (‘Bradshaw’, I should explain, was the standard railway handbook of the day):

The aeroplane was so knew that it had not yet been fitted with a compass. I was ‘flying by Bradshaw’, following the railway lines across the country, and I wondered if I could fly by the sun. The sky was overcast…I climbed up into the cloud, and proceeded until I had passed through a 9,000-feet layer of it to emerge at 10,000 feet in brilliant sunshine over a snowy-white field of cloud. Not only had I no compass, but no blind flying instruments at all…After flying along for half an hour by the sun, I climbed down through the 9,000-feet layer of cloud. I then wanted to find out how accurately I had carried out this manoeuvre, and I used a sound principle of navigation. I fixed my position by the easiest method available – I flew round a railway station low down, and read the name off the platform. By some extraordinary fluke I was right on course. I probably uttered for the first time the navigator’s famous cry ‘Spot on!’

From The Lonely Sea and Sky, Chapter 7. (Hodder and Stoughton, 1964)

10.Barry Lopez on polar bear navigation

In his classic work, Arctic Dreams, Barry Lopez occasionally refers to the remarkable navigational abilities displayed by animals of the far north. Polar bears for example:

“ Bears make use of mountain passes, ravines, and other features of the land in such a way as to suggest that these are traditional routes…

” Beyond using celestial clues and a knowledge of prevailing winds and currents, which reliably guide Eskimos across the angular topography of shifting sea ice, no one knows how bears find their way. But they consistently travel directly to aggregations of seals; they return to core denning and breeding areas every year; and they find their way unerringly to the coast from hundreds of miles offshore. This would be astonishing enough if they only did it on land, where there are perennial landmarks, but they also do it at sea, where a frozen landscape is created anew each year, which can change from one day to the next… In some areas of stable ice, bears may travel for weeks without seeing a break in the continuity of the sharp blue line of the horizon…” [from Chapter 3, Tôrnâssuk.]

Maybe, as Lopez suggests, the bears do indeed use celestial cues, like the azimuth of the sun. Maybe they also know about prevailing winds or currents. It’s equally possible that they use their acute sense of smell. Lopez also speculates that the bears make use of maps in their heads - or cognitive maps - but I’m not sure the evidence really supports such a claim. Perhaps they are just good at DR? In any case, the secrets of polar bear navigation are one more mystery to add to my growing personal list of puzzles!

9.‘Incredible Journeys’ is now out in paperback in the UK

It’s also available as an audiobook - read by the author!

8. a video introducing ‘Incredible Journeys’ (‘Supernavigators’ in North America)

This is a 15-minute version of a video I made recently as an introduction to some of the main themes of the book. I hope you enjoy it!

7.Celestial navigators - human and non-human

People have been using the sun, moon and stars to help them find their way for a very, very long time.  

And not just people but other animals too – like birds, moths and beetles – to name but a few.  This is a really exciting area of research and new discoveries keep piling in, many of which are described in Incredible Journeys.

Eric Warrant and Marie Dacke, for example, have shown that nocturnal dung beetles roll their carefully sculpted dung balls back to their nests using the light of the moon or the Milky Way as a guide.  

And recently Eric Warrant and David Dreyer have shown that the Australian Bogong moth also makes use of the Milky Way to maintain a steady course on its 1000 km migratory journeys (as well as a magnetic compass).

Bogong moth

We know that many birds that migrate by night orient themselves by paying attention to the rotational pattern of stars around Polaris, which marks the direction of true north.

My guess is that our prehistoric human ancestors would also have been pretty good at this kind of celestial navigation - tens of thousands of years ago.

What we know for sure is that the builders of Stonehenge and many other ancient monuments around the world are carefully aligned so as to highlight key celestial events like the summer and winter solstices – that mark the longest and shortest days of the year.  

And the amazing Nebra Sky Disc – discovered in Germany in 1999 – suggests that our Bronze Age forebears understood the very complicated relationship between the solar and lunar years.  It was made about 3,500 years ago. http://www.bibliotecapleyades.net/arqueologia/nebra_disk.htm

And the Greeks knew a thing or two.  The amazing Antikythera Mechanism – discovered by sponge divers over a hundred years ago – dates from around the end of the 2nd century B.C.  It’s by far the most sophisticated mechanical device yet discovered from the ancient world. The Antikythera Mechanism seems to be a complex mechanical “computer” which tracks the cycles of the Solar System: https://en.wikipedia.org/wiki/Antikythera_mechanism

We know frustratingly little about how the Greeks and Romans navigated at sea, though they travelled widely - and not just in the Mediterranean.  It’s always assumed that they didn’t use any specialised equipment.  But the Antikythera mechanism makes you wonder…if they knew that much about the behaviour of the heavens, would they not have put their expertise to navigational use?

On the other side of the world the islanders of the Pacific were already starting to venture out across the Pacific at least two thousand years ago. In their ocean-going sailing canoes they could make accurate landfalls on small islands after travelling as much as two thousand nautical miles across the open ocean.  

They didn’t use any instruments or even charts.  They relied only on their wits and finely-tuned senses – and a lengthy apprenticeship that started when they were children.  When western sailors like Bougainville and Cook first encountered these navigational prodigies in the mid-18th century they were astonished.  

Luckily we know a lot about how the Pacific Islanders navigated because, back in the 1960s, researchers started asking the right questions - before their extraordinary skills had completely died out.  

At the heart of traditional Micronesian and Polynesian navigation was an encyclopaedic knowledge of the sky.  The master navigators knew exactly where on the horizon 32 bright stars rose and set, and they could steer a steady course by reference to them.  They also understood that Polaris indicated where true north lay and during the day they could steer by the light of the sun by accurately allowing for the its gradual movement across the sky. They had many other remarkable skills and happily these are now being widely practised once more: http://hokulea.org

Before electronic aids like GPS arrived on the scene, navigators everywhere learned to observe the world around them very closely.  The colour of the water and its depth, the composition of the seafloor (tested with a lead-line), the behaviour of birds, the shape and colour of clouds – these and many other signs could give early warning of the presence of land, often long before it could be seen.

In former times, sailors everywhere paid the closest attention to the world around them - as well as the skies above them. Safe navigation depended on complete immersion in the natural world. It may not always have been as safe or reliable as navigating by GPS, but it was a far richer and much more rewarding experience. And it was also a great deal more robust: no problems like flat batteries, solar storms, spoofing or jamming!

6.The author of the ‘The Call of the Wild’ on celestial navigation…and the dangers of pride!

Jack London

https://www.falseart.com/jack-london-the-snark/

As readers of my first book, Sextant, will know, I’m not only interested in how non-human animals navigate. I’m a navigator myself and a devotee of celestial navigation - a skill seriously threatened by our increasing (and by now almost exclusive) reliance on electronic navigation aids, notably GPS.

So here’s an entertaining anecdote drawn from the author and adventurer Jack London’s account of his long trans-Pacific cruise in his yacht the Snark.

London and his friend, Roscoe, sailed from San Francisco in 1908 – heading first for Honolulu – without yet knowing how to use a sextant, which was a problem because they had no other way of determining their position!  So they simply taught themselves.

Roscoe was the first to try his hand:

‘…when we got out to sea and he began to practise the holy rite, while I looked on admiringly, a change, subtle and distinctive, marked his bearing.  When he shot the sun at noon, the glow of achievement wrapped him in lambent flame.  When he went below, figured out his observation, and then…announced our latitude and longitude, there was an authoritative ring in his voice that was new to all of us.  But that was not the worst of it.  He became filled with incommunicable information.

‘By an understandable and forgivable confusion of values, plus a loss of orientation, he felt weighted by responsibility, and experienced the possession of power that was like unto a god…The act of finding himself on the face of the waters became a rite, and he felt himself a superior being to the rest of us who knew not this rite and were dependent on him for being shepherded across the heaving and limitless waste, the briny highroad that connects the continents and whereon are no milestones. So, with the sextant he made obeisance to the sun-god…’

At first London deferred to Roscoe, but quite soon he rebelled.  Roscoe, he reflected, is a man like myself.  ‘What he has done, I can do.’  So he decided to learn for himself how to handle a sextant – a task that he found not too difficult.

‘The mystery was mystery no longer. …and yet, such was the miracle of it, I was conscious of new power in me, and I felt the thrill and tickle of pride… I was not as other men – most other men: I knew what they did not know, – the mystery of the heavens, that pointed out the way across the deep….No medicine man nor high priest was ever prouder…I was a worker of miracles. I forgot how easily I had taught myself from the printed page. I forgot that all the work (and a tremendous work, too) had been done by the masterminds before me, the astronomers and mathematicians, who had discovered and elaborated the whole science of navigation…’

Eventually the Snark made her first landfall, just as planned:

‘ “That island is Maui”, we said, verifying by the chart. “…We’ll be in Honolulu tomorrow. Our navigation is all right.” ‘

[Quotes from The Cruise of the Snark by Jack London]

5.The night and stars: Henry Beston on Cape Cod in the 1920s

‘With lights and ever more lights, we drive the holiness and beauty of night back to the forests and the sea; the little villages, the crossroads even, will have none of it. Are modern folk, perhaps, afraid of night?  Do they fear that vast serenity, the mystery of infinite space, the austerity of stars?…Be the answer what it will, to-day’s civilization is full of people who have not the slightest notion of the character or the poetry of night. Yet to live thus, to know only artificial night, is as absurd and evil as to know only artificial day.’

from ‘The Outermost House’, Chapter 8: ‘Night on the Great Beach’

4.How do whales navigate?

A recent article in The Atlantic discusses the fascinating possibility that whales make use of the Earth’s magnetic field to help them navigate the oceans.

As I explain in Incredible Journeys, many great whales (including notably the humpbacks that migrate annually between the Antarctic and equatorial waters) regularly travel for thousands of miles across the apparently featureless open ocean following remarkably straight courses. Since they seem to be able to do this even when the sky is obscured, it seems unlikely that they rely on celestial cues (like the sun or stars) to perform these feats - though it’s conceivable that they can do that too in fine weather. The omnipresent geomagnetic field (see my earlier post ‘The great magnetic mystery’) would however be available to them at all times and places - and all depths.

The theory that whales may be magnetic navigators (like many other animals including some birds and insects) has been around for a long time. But Jesse Granger and her colleagues at Duke University have recently published some interesting work based on a review of data gathered over a 31-year period. They wanted to find out whether solar storms that disrupt the Earth’s magnetic field are correlated in any way with strandings of gray whales.

They looked at 186 strandings involving apparently healthy whales (injured or sick animals might get stranded for other reasons) and parallel data relating to levels of solar activity. They found that the two were indeed closely correlated.

So what’s going on?

As Granger et al. explain, ‘Solar storms could have two impacts on magnetic orientation. They could alter the geomagnetic field, leading to false information, or disrupt the animal’s receptor itself, leading to an inability to orient.’ But the key factor influencing the strandings appeared to be the increase in radio frequency ‘noise’ associated with the solar storms rather than any displacement of the Earth’s magnetic field.

Granger et al. conclude: ‘These results are consistent with the hypothesis of magnetoreception in this species, and tentatively suggest that the mechanism for the relationship between solar activity and live strandings is a disruption of the magnetoreception sense, rather than distortion of the geomagnetic field itself.‘

There is evidence from studies of migratory robins that RF noise (from AM radio transmitters) can disrupt the magnetic compass sense of these birds. It’s possible that the hypothetical cryptochrome magnetoreception mechanism may be disrupted by such transmissions. So, as Granger et al. acknowledge, it’s conceivable that whales may also rely on a cryptochrome-based magnetoreceptor. But it’s far too soon to start laying bets!

One thing that puzzles me is that gray whales - which tend to follow the coast on their migratory journeys rather than crossing the open ocean - should be so heavily reliant on magnetic information that they would get stranded if it was disrupted. Could they not simply use landmarks or the contours of the sea floor to help them find their way? And even if they did rely on their magnetic sense of direction, you’d think that they would notice when the water began to shoal and turn back before they went aground. It’s odd.

The humpbacks by contrast are prodigious oceanic navigators and it makes sense that they would rely on geomagnetic cues when out of sight of land. Interestingly their migratory journeys often seem to feature visits to underwater features called seamounts. Could it be that these act as waymarks? Maybe they even have unusual magnetic properties that the whales can detect?

Apparently Granger is now looking at 12 years-worth of data relating to humpback whale voyages. She wants to see whether they have more difficulty maintaining straight courses when solar storms hit the Earth.

That should be interesting!

3.'Dead reckoning’ - from sailors to crabs...

Until the advent of GPS, sailors relied heavily on a navigational technique called ‘dead reckoning’ (DR) to keep track of their position when out of sight of land. (NB: Scientists prefer the term ‘path integration’ but it’s essentially the same thing.)

Though the origins of this ancient term are mysterious, DR is simple - at least in principle. You record your ‘course’ (the direction in which you’re headed according to a magnetic compass) together with the distance you have travelled (estimated with the help of a ‘log’ and a clock - or even just an hour glass). You can then - in theory at least - reconstruct the course you have followed and work out where you are in relation to your point of departure. And if you have a chart you can plot your position on it.

Unfortunately DR is in practice quite unreliable. Not only is it hard to steer an arrow-straight course, but the open ocean is very far from being a stationary mass of water. There are currents, which are sometimes strong and often unpredictable. And it’s difficult to detect them unless you have an independent means of fixing your position. Old-fashioned logs were also dodgy. They consisted of small triangles of wood attached to a long rope marked at regular intervals with ‘knots’. The ‘log’ was dropped over the side and the rope allowed to unspool for a fixed period of time. The number of ‘knots’ that ran out indicated your speed through the water. But this technique was not very accurate, especially in heavy weather. As a result, the longer you were at sea, the more uncertain you were about your exact position.

But over short distances DR can work quite well. And lots of animals make successful use of it.

The best-studied example is the desert ant of the Sahara (Cataglyphis fortis).

The great German scientist, Rüdiger Wehner, has spent the best part of 50 years exploring the astonishing navigational tools used by Cataglyphis. At the heart of these is a DR system based on the ant’s ability to detect patterns of polarised sunlight in the sky. These patterns (invisible to us) enable the ant to keep track of the course it is following as it canters over the baking, featureless salt flats in search of its prey - usually dead insects. In effect it has a built-in celestial compass.

But a compass alone is not enough for DR. You also need some way of measuring how far you have gone. In other words, an odometer. And, as I explain in Incredible Journeys, Cataglyphis has an odometer based (in part at least) on its ability to keep track of how many steps it has taken!

The desert ant’s impressive DR system allows it to head straight for its nest even after wandering erratically over hundreds of meters. And bear in mind that its nest entrance is no more than a tiny hole in the ground. It is quite invisible to the ant until it gets very close to it. Quite a feat!

Lots of other insects - including honey bees - also use a celestial compass based on polarised sunlight. Some nocturnal ones even make use of polarised moonlight or the orientation of the Milky Way! Obviously flying insects don’t count their steps. Their odometers work differently. I’ll come back to this intriguing subject on another occasion.

Let me finish this post by mentioning another, very different animal that makes use of DR: the fiddler crab (Uca rapax).

These animals are a common sight on the coasts of Central America and the Caribbean where they live underground and usually only go out to find food. The crabs need to get back to the shelter of their burrows quickly when they perceive a threat and they do this very well.

Fiddler crabs are really remarkable. As they wander around, and no matter how complicated the route they follow, they always point their bodies (sideways) towards their burrows. And, by playing various tricks on them, scientists have shown that - unlike desert ants - they don’t make use of visual information to maintain this homeward orientation.

First the researchers placed crabs on discs and spun them around. The crabs didn’t much like that and tried hard to counteract the rotation. But they didn’t always succeed and sometimes, for all their efforts, they ended up pointing in the wrong direction. The extent of their homing error depended exactly on how far they had failed to compensate for the rotation.

Now if the crabs’ homing ability was based on some external cue - like polarised light or the position of landmarks - they would have been able to correct their orientation after being rotated.

The same researchers next tried putting a patch of slippery plastic in the path of the crabs as they headed for home.

Some crabs had difficulty getting traction on the plastic and scrabbled to get across it. This meant that they took a number of steps without making much progress. These ones ended up stopping short of their burrows - suggesting that they had overestimated how far they had travelled. By contrast, those that crossed the obstacle without losing their grip, stopped in just the right place - as did controls that didn’t have to cross the plastic sheet at all.

So what does all this mean?

On the basis of these findings it looked very much as if fiddler crabs performed DR by paying attention primarily to the movements of their own bodies - specifically how many steps they had taken and the angles through which they had turned. That’s a pretty sophisticated system and one that we humans certainly can’t match - at least not without the help of technology.

More recent research has confirmed that the fiddler crab’s DR skill does indeed depend on their ability to count their steps.

More soon…

2.‘Incredible Journeys’ shortlisted for prize

I was really delighted to hear today that ‘Incredible Journeys’ was on the shortlist for the Richard Jefferies/White Horse Bookshop literary prize for nature writing. The full shortlist is here under ‘latest news’. The winner won’t be announced until May.

I can now reveal (June 2020) that ‘Incredible Journeys’ did not win, alas! But it was good to be on the short list.

1.The great magnetic mystery...a new development

Lots of animals use the earth’s magnetic field to help them find their way around. They range from newts, lobsters and ants to birds, fish and marine turtles. So it looks as if magnetic navigation has a very ancient evolutionary lineage.

But we still don’t know for sure how it works.

As I explain in ‘Incredible Journeys’, there are two main theories - which are not mutually exclusive.

The first is fairly simple. The idea is that animals make use of particles of magnetic minerals (typically magnetite) inside their bodies. As the animal moves through the earth’s magnetic field these particles are subjected to minute forces that twist or pull on them.

If the animal has sensory nerves hooked up to the particles, it may be able to detect these forces and infer something useful about the character of the surrounding field. Some scientists think that a mechanism like this could even enable an animal to work out roughly where it is, though that is quite controversial.

A very different theory has been attracting a lot of attention recently (partly perhaps just because it’s so difficult to pin down). The idea here is that a light-dependent subatomic process may be involved.

Certain molecules (cryptochromes) react to the impact of a photon of light by briefly generating a so-called ‘radical pair’ of electrons. In theory, the behaviour of such a ‘radical pair’ could be affected by the orientation of the surrounding magnetic field. If these extremely subtle changes could somehow be picked up by the animal’s nervous system, they might provide the basis of a biological compass.

It’s even been suggested that migrating birds (which have cryptochrome molecules in their eyes) might ‘see’ the surrounding magnetic field superimposed on their visual field - a bit like a pilot’s head-up display. Wow! Well, at the moment this remains only a promising theory.

But there is another intriguing possibility that I allude to briefly in my book. It hasn’t received much attention until recently but it’s just received a bit of a boost. This involves the principle of electromagnetic induction.

If an electrical conductor is moved through a magnetic field a current is induced within it (this is how dynamos work). Oddly enough, it looks as if the fluid-filled semi-circular canals of the inner ear may operate in a similar way.. A new piece of research from David Keays’ lab in Vienna suggests that electric currents induced in the semi-circular canals of the homing pigeon could be the basis of the magnetic compass which the birds use.

It’s early days, but if this turns out to be right, it will be a very significant breakthrough.

Watch this space…