Research just published shows that migratory Painted Lady butterflies (Vanessa cardui) found on the coast of South America had crossed the Atlantic from West Africa - and might even have started their journeys in Europe. That means they may have travelled - in total - 7000 km or more! Astonishing, even by comparison with the mighty Monarch butterfly, though the Painted Ladies would have been helped on their way by the Trade Winds.
Our abuse of the natural world is causing problems which grow more terrifying with every passing day.
Understandably, climate change and the physical destruction of entire ecosystems attract the most attention.
But we face another environmental threat - one which is insidious and fast-growing, yet still widely ignored.
Light pollution.
The world we inhabit was, until modern times, governed by strict astronomical laws. Day followed night, and the night was always dark - except when the moon was full. This celestial regime shaped the behaviour and biological rhythms of (almost) every living thing on the planet.
The coming of electric light changed everything - and continues to do so. In many places true darkness now never comes. And while we may welcome that change because some of our deepest fears are associated with darkness, all that new light is causing immense damage.
There is overwhelming evidence of the destructive effects of artificial light on the animals (and plants) with which we share the planet.
To give just a few examples, it is likely that billions - yes, billions - of migratory birds die when they are drawn to brightly lit buildings. And even that number is dwarfed by the number of insects that suffer a similar fate. Then there are the countless, doomed turtle hatchlings that are lured away from the sea by artificial light.
Light pollution is a major but little-noticed factor in the massive problem of biodiversity loss.
Moreover it is increasingly clear that by banishing darkness we are also damaging our own health and well-being.
Exposure to artificial light at night is associated with a host of physical and mental disorders including diabetes, depression and even some forms of cancer.
And we are suffering other, less tangible but important injuries.
The darkness that once permitted everyone on the planet to see thousands of stars, as well as the glowing ribbon of the Milky Way - our home galaxy - has been obscured by the halo of artificial light that surrounds every town and city. The arrival of the LED has only made matters worse.
Most people living today will never see the night sky in all its glory.
The facts are not in dispute. In some countries (France, for example) governments are already taking practical steps to address the problems of light pollution. In the US there are many cities that have taken steps to reduce the glare of outdoor lighting.
But the British government rejected an amendment to the recent Environment Act that would have added the reduction of light pollution as a target.
Low public awareness is a major obstacle, coupled with the common assumption that more light must be better, and a widely held (but questionable) belief that it always improves our security.
Few people realise that the worst effects of light pollution can be reduced or eliminated by taking a few simple, inexpensive steps - such as installing lights with warmer colours, shielding them so that they don’t not spill upwards into the sky, and using motion sensors so that they only come on when needed.
The best solution of all - just turning unnecessary lights off - has the great additional benefit of saving both energy and money.
Often it is enough to draw someone’s attention to the problems. I recently persuaded the British Army to remove some outrageously bright lights from a military base in the middle of Chichester Harbour (a nature reserve on the South Coast of England) simply by having a conversation with the senior officer in charge.
In the UK, the Council for the Protection of Rural England’s (CPRE) annual ‘star count’ has helped people become more aware of the problem of ‘skyglow’ - and it’s good news that several Dark Sky Parks have been designated in the UK.
But while some UK charities take an interest in light pollution, none treats it as a priority. Because all their efforts are small and fragmented, progress in tackling the problem has been painfully slow.
Much more needs to be done.
So here are a few ideas:
Why don’t British environmental charities devise and adopt a code of conduct in relation to light pollution?
Why don’t those same charities ask all their grant recipients to follow a similar code of conduct? Perhaps they could offer extra funding for this purpose.
A good way of raising public awareness in the UK would be to establish an annual prize in recognition of outstanding achievements in tacking light pollution. Who would like to take this on?
Above all, policy change is needed. Will one of our leading environmental charities launch a campaign to get the government to regulate light pollution?
Yes, it’s a big challenge, but it’s also an urgent one.
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’!
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!
Off the coast of Portugal a week or two ago…
I’ve been away for a while, on the high seas, doing some real navigation in the Mediterranean and Atlantic - and tasting a bit of freedom after all those months of lock-down. Good to see some wildlife too: lots of Cory’s shearwaters, dolphins, green turtles (a few), a humpback whale breaching, swordfish leaping…even an errant hoopoe heading south towards the distant shore of Africa. I hope it made it!
Now I’m home again, I’ve been catching up on the latest research. Here are a few highlights that caught my eye.
First, there was this paper about magnetoreception from Jingjing Xu et al. This strengthens the case for cryptochrome molecules in the retina of night migratory birds being the basis of their magnetic compass sense. This theory - which I also discuss in Supernavigators/Incredible Journeys - is the subject of enormous research interest at present. Eric Warrant has provided a really good commentary that explores the significance of this piece of research. As he explains, Xu et al. have made a major advance by showing that ‘the version of CRY4… in the migratory European robin has a crucial property needed to sense Earth’s magnetic field: the ability to form radical pairs that have high magnetic sensitivity’. Moreover, they have demonstrated that CRY4 is more sensitive in the robin than it is in other, non-migratory birds.
Then there was this fascinating article by Eliav et al. about how bats navigate. Up until now, most of what we know about how the brains of mammals support their ability to navigate has come from laboratory-based studies of rats and mice (and humans). Nachum Ulanovsky and his colleagues in Tel Aviv have however developed wireless techniques for recording the activity of single cells in the brains of bats on the wing! This latest paper shows that single place cells (which ‘represent’ the positiion of an animal in space) in bats flying through a long tunnel can operate on a range of scales - from about 1m to 30m. This multiscale coding provides a really efficient way of representing large environments of the kind that bats inhabit. It will be very interesting to see what emerges when this kind of research is extended to other animals that navigate over long distances - like birds.
Finally I want to mention a piece of research that touches on something that really bothers me: the scourge of light pollution. In this paper, James Foster et al. have shown how light pollution can seriously interfere with the navigation of nocturnal dung beetles - which rely on polarised moonlight and the orientation of the Milky Way to maintain a straight course as they roll their balls of dung. They found that ‘that light pollution…induces dramatic changes in dung beetle orientation behavior, forcing them to rely on bright earthbound beacons in place of their celestial compass’. The beetles are attracted toward artificial lights, and this results in more competition between individuals and reduced dispersal efficiency. As the authors rightly observe, ‘for the many other species of insect, bird, and mammal that rely on the night sky for orientation and migration,
these effects could dramatically hinder their vital night-time journeys’.
This important article by Van Doren et al. also relates to light pollution. Based on historical records at a site in Chicago, it suggests that bird deaths caused by collisions with lighted buildings could be substantially cut by reducing lighting to more sensible levels.
Here also is a link to good BBC article about the problem of light pollution.
That’s all for now.
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.
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.
Sandhopper (Talitrus saltator) - photo courtesy Arnold Paul / edited by Waugsberg and Buchling / CC BY-SA 2.0 DE (https://creativecommons.org/licenses/by-sa/2.0/de/deed.en)
We’re only just starting to realise that our love affair with artificial light at night (ALAN) is bad not just for us, but also for many of the creatures with which we share this planet. Including, for example, the sandhopper.
But before I talk about the problems facing this remarkable crustacean, let me sketch in a bit of background about light pollution.
Paris was the first European city to introduce street lighting. That was in 1667, during the reign of Louis XIV - The Sun King. Very soon other major cities across Europe followed suit. (I’m not sure about Asia - I suspect that Edo was pretty well lit too and maybe even earlier than Paris. Does anyone know?)
Streetlights in those days were pretty dim - just candles or oil lamps. While they made nocturnal city life easier and perhaps a bit safer, they didn’t have much effect on the visibility of the night sky. In the countryside, the nights remained as dark as they had always been.
Things changed with the arrival of gas and electric lights in the 19th century. Cities could now be brilliantly illuminated. More light seemed to be an unqualified good, and few resisted its encroachments. Today of course we have many other kinds of lighting - like LEDs and fluorescent tubes.
ALAN is spreading rapidly across the face of the earth. Everywhere you go, there are brilliantly lit office buildings, factories, airports, docks, military installations, car parks, apartment blocks and even private houses.
But ALAN is not restricted to built-up areas - it extends outwards along the roads that connect the cities and towns where we live. You can’t even escape it completely on the open ocean, where oil rigs, ships and fishing boats are often lit up like Christmas trees.
The problem is not just the direct glare of the lights themselves.
There is also the phenomenon of ‘skyglow’ caused by the scattering of light from clouds and dust in the atmosphere.
One of the sad consequences of ALAN is that most people on earth can no longer enjoy the wonder of a dark night sky with its thousands of stars - and they will never see the Milky Way.
Big cities generate so much light that the skyglow above them can sometimes be detected a hundred miles away or more. It is the most widespread form of light pollution and apparently now affects 23% of the earth’s surface between the latitudes of 75 degrees North and 60 degrees South. That includes many of the most important areas of biodiversity around the world. And it continues to spread rapidly.
Of all the many serious environmental problems we face, ALAN is actually the easiest to solve.
Better designed lights, properly shielded, pointing in the right direction, and only as bright as they need to be, would make a huge difference. Steps like these would not be expensive to implement. They would also save energy and reduce costs in the long run. (For more information about light pollution and how to combat it, visit the excellent website of the International Dark-Sky Association.)
In recent years scientists have begun to pay attention to the effects of ALAN, both on us humans and on other animals, as well as plants.
ALAN certainly has a disruptive effect on the internal clocks that govern many natural processes - including our own sleeping patterns.
It is a well-known menace to turtle hatchlings, as well as migratory birds. It may also be implicated in the decline of many insect species.
And now it looks as if ALAN is also making life difficult for the poor little sandhopper.
These animals live on sandy beaches and, as I explained in Incredible Journeys (Chapter 10), they are remarkable navigators.
In the evening they make their way to water’s edge to chomp on seaweed. In the morning they retreat up the beach and bury themselves in the damp sand to avoid getting dried out by the sun. Since they can easily get drowned, it’s important that they don’t go the wrong way.
Amazingly, sandhoppers have not one but two celestial compass systems that help them steer in the right direction - whether up or down the beach. One is based on the light of the moon and the other on the sun.
A new study (unfortunately locked behind a paywall) from D. Torres et al. looks at how skyglow affects the navigational ability of sandhoppers on the coast of the island of Anglesea, Wales.
They report that skyglow - though much weaker than direct light pollution - nevertheless disrupts the sandhoppers’ lunar compass system, making it harder for them to navigate safely at night.
Since many other animals use the stars and the moon to help them orient at night, it is a sure bet that ALAN is not just causing trouble for sandhoppers.
Torres et al. conclude that ‘a renewed focus on the ecological impacts of artificial skyglow is urgently needed’ in order to understand how it is affecting the world around us.
Yes indeed.
And in the meantime, please do think about how you can reduce your own light footprint!
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!
Dogs may be interesting, but whales are really fascinating!
In Incredible Journeys I wrote about the mysteries that surround the extraordinary navigational feats of humpback whales.
And I mentioned the possibility that whales might be making use of gravitational information.
How could that possibly work?
Well, roughly speaking, the idea is that these huge beasts may be able to track changes in their buoyancy resulting from alterations in the gravitational forces to which they are subject.
These changes may result from anomalies in the bedrock beneath the ocean, changes in latitude, or astronomical influences - like tidal forces and the varying distance between the earth and moon.
An ability to detect gravitational patterns in the submarine landscape would obviously be navigationally useful. And if the whales are also aware of changes in the earth-moon gravitational system, those could perhaps help them time the start of their migratory journeys.
Now some new research from Travis Horton and his colleagues has shed more light on these intriguing ideas.
Horton and his team have been sifting evidence about the migratory behaviour of humpbacks travelling between their calving grounds on the Abrolhos Bank (in the tropical seas off the coast of Brazil) and their feeding grounds far to the south, in the chilly waters of the South Georgia Basin.
The data come from old Soviet-era records of whale-hunting activities (bizarrely hidden for many years in a potato cellar!), and more recent satellite-based tracking studies.
These records, which stretch back 50 years or more, show that the whales have continued faithfully to follow the same migratory ‘corridor’ - despite the fact that the relevant geomagnetic and oceanographic conditions (eg currents and food availability) have varied greatly over that period.
As Horton et al. put it, ‘humpback whale migrations do not change in a changing ocean’.
After carefully analysing the tracking data, the team conclude that the whales follow ‘richly patterned and highly reproducible trajectories’. Moreover, these trajectories do indeed appear to reflect the varying gravitational forces to which the animals are subject.
They also found that the tracked whales fell roughly into two groups: those that tended to travel relatively fast and those that travelled at a more sedate pace.
Interestingly, eight of the nine ‘slow’ whales started their southbound migrations just before or during the first or last quarter of the moon. By contrast, eleven ‘fast’ whales head south near the full or new moon. Curiously, the whales that ‘sang’ swam more slowly than the non-singing ones. I wonder why?
While lending weight to the theory that the whales make use of gravitational information, this research certainly doesn’t rule out the possibility that the whales also make use of geomagnetic information - as several earlier studies have proposed. It does however suggest that they don’t rely exclusively on magnetic cues. And this would certainly make good sense if, as in this case, those cues are constantly changing.
White-fronted goose
You’ve probably seen geese flying in a tight V-formation, and you may have wondered why.
It seems that the upwash from the wings of the lead bird gives a bit of extra a lift to the birds following on either side, and thus reduces their energy consumption - an effect that continues down the line to the tails of the V. That really matters on a long migratory journey, but the lead bird obviously has to work a bit harder than the rest. So it came as no surprise when some recent studies showed that birds took turns in taking the lead, thus sharing the extra burden.
But something slightly different emerged from a fascinating new study.
Researchers attached lightweight GPS trackers and accelerometers to wild white-fronted geese belonging to four family groups setting out on their long migration from the Netherlands to northern Russia. This meant that they could not only see exactly where each bird was in the formation, but also how fast they were flapping their wings.
It turned out that only the parents ever took the lead. Usually the father, but sometimes the mother - depending on the wind conditions. The mothers had to flap their wings faster when they were out in front, but the fathers apparently did not need to.
It makes good sense for the parents to take on this leadership role, because it increases the chances of their offspring surviving the rigours of the long journey - and thus having a chance to pass on their genes to future generations (so-called ‘kin selection’).
But this system probably also helps the young, first-time migrants to learn the route they need to follow in future, where best to stop for refuelling, how best to avoid dangers - and indeed how to fly most efficiently.
In groups of homing pigeons, less experienced birds follow more experienced flock members, and this helps them to learn routes. Further experiments will be needed to see whether this is also true of young migratory geese.
A couple of weeks ago I wrote about the amazing journeys undertaken by adult Mongolian cuckoos - like Onon in this picture.
Here I talk very briefly about a fascinating new study, just published in the journal Nature. It reveals that young cuckoos - making their very first migratory journey all the way from Russia to Southern Africa - can somehow tell when they have been moved 1800 km to the east of their proper route. And, just like experienced adult birds, they can change course to compensate for this displacement.
It’s the first time such an ability has been clearly demonstrated in young birds and it leaves us wondering how they solve a problem that we humans only cracked a few hundred years ago.
DB talking to Clare Clark
I was lucky to be interviewed by the novelist Clare Clark who asked extremely good questions. I hope my answers measured up to them!
There’s no better way of getting a sense of what migratory birds can do than to look at the maps that record their journeys.
The Mongolian Cuckoo Project has been using tracking devices to follow the amazing journeys of cuckoos returning home from Southern Africa in recent weeks. Do please visit their excellent website to see the achievements of Onon, Bayan and the other birds. It’s a real model of public engagement in science.
Quite apart from the extraordinary distances the birds have been covering, I’m struck by the close similarity between the routes they have been following. It would be fascinating to know exactly how they perform such impressive navigational feats.
Presumably, like many other migratory birds, cuckoos have a sun and star compass as well as a magnetic one. And when they have made their first migratory journey, it’s safe to assume that they use familiar landmarks to help them retrace their route. But of course there are no landmarks over the ocean!
And cuckoos face a special problem. Their unusual lifestyle means that when they first head south, they must do so alone - because their parents will have left before them.
So how on earth do they find their lonely way over thousands of miles of land and ocean to the areas in Africa where they pass the winter months? Some kind of genetic program must be involved. But how does that work? We just don’t know.
One last thing: why not lend your support to this brilliant project by following this link?
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!
