57. How do whales navigate: part 2

When I last wrote on this subject (see blog #4) I focussed on the possible role of geomagnetism in helping humpback whales to navigate across oceans with remarkable precision.

Recently I came across an article (dating from 2020) that raises another possibility.

Perhaps migratory fish - which are known to be sensitive to infrasound (very low frequency sound below the threshold of human hearing) - make use of it to orient themselves?

The idea is that turbulence caused by ocean currents or seismic activity in the ocean floor (eg along mid-ocean ridges or around submarine volcanoes) gives rise to characteristic infrasound signals that are capable of travelling over great distances. Breaking waves along a coast are another infrasound source.

Any marine animal that can detect such sounds could in principle extract useful navigational information from them.

We know that many animals other than fish (including eg birds and elephants) can detect infrasound, so the possibility that whales may do so too seems plausible.

To the best of my knowledge, this idea remains speculative (it’s hard to experiment on whales!) but it’s not a big leap to imagine that whales (as well as migratory fish) may navigate with the help of infrasound.

Of course that wouldn’t conflict with the possibility that they may use geomagnetism. The two systems would complement each other well.

47. How do migratory birds make use of the earth’s magnetic field? →

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.

46. Einstein, von Frisch and the honey bee…

Professor Miguel Sanjuan, of the Universidad Rey Juan Carlos, has kindly brought to my attention this fascinating recent article from the Journal of Comparative Physiology A (https://doi.org/10.1007/s00359-021-01490-6).

In 1949 Albert Einstein attended a lecture that Karl von Frisch gave at Princeton University about the extraordinary navigational abilities of the honey bee. The discovery that bees make use of polarised light to help them locate food sources, as well as communicating by means of a dance language, caused a sensation. A British radar engineer, Glyn Davies (who later became an actor), apparently wrote to Einstein to ask for his comments on this breakthrough, though his letter is lost.

Following Davies’s death, however, Einstein’s reply to him has come to light. In it he makes the following prescient remark:

”It is thinkable that the investigation of the behaviour of migratory birds and carrier pigeons may some day lead to the understanding of some physical process that is not yet known.”

As the authors of the article observe, Einstein would surely have been very excited to know of all the work currently being undertaken to determine exactly how different animals - including migratory birds and pigeons - detect the geomagnetic field (see blog 1 below), as well as the many discoveries that have been made since the 1940s in the fields of animal perception and navigation.

An image of Einstein’s typewritten letter is included in the article.

36. Do Manx shearwaters make use of magnetic inclination to find their way? →

Here’s a fascinating short talk given by Joe Wynn at today’s Association for the Study of Animal Behaviour Virtual Conference.

Wynn discusses recent research that sheds light on how Manx shearwaters - prodigious oceanic navigators - find their way home to their breeding colonies.

As you’ll see, these birds - like sea turtles and salmon - apparently learn the magnetic signature of their place of birth (specifically the local magnetic inclination). They then use this information to help them return home.

But sometimes the birds end up in a slightly different place because the earth’s magnetic field has altered in their absence. In fact, it is these very errors that reveal the crucial role magnetic inclination plays in their navigational behaviour.

If you want to read the original research, here’s the reference:
Wynn et al., 2020, Current Biology 30, 1–5 July 20, 2020 a 2020 Elsevier Inc. https://doi.org/10.1016/j.cub.2020.05.039

28.Green turtles aren’t perfect navigators - but they don’t have to be

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!

26.New light on whale navigation

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.

18.My interview for the Stratford Literary Festival

I was lucky to be interviewed by the novelist Clare Clark who asked extremely good questions. I hope my answers measured up to them!

17.Amazing cuckoos

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?

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!