A butterfly’s navigational clock is not in its brain. It is in its antennae.
Animals navigate using several overlapping compasses — sun, stars, polarised light, smell and magnetic field — and knowing which way is north is a different problem from knowing where you are.
Navigation is the capability where popular explanation and evidence part company most cleanly. It is routinely said that animals "have a magnetic sense", as though one settled mechanism did the work. What the research shows is redundancy: a monarch butterfly runs a sun compass whose clock sits in its antennae, a desert ant counts its own strides, a honey bee argues the field to a standstill over whether it holds a map, and a loggerhead hatchling that has never migrated orients correctly for a magnetic signature it has never encountered. The compasses are well established. How the magnetic field is detected is not, despite half a century of work — and whether any animal holds a true positional map is genuinely open.
Developed coverage · 77% complete · reviewed 2026-09-03
What this page covers
A capability rather than an organism. Covers orientation and route-finding wherever it has been directly tested — insects, birds, reptiles and mammals.
Quick facts
Kind
A capability page, assembled from evidence across species
Compasses
Sun, stars, polarised light, olfactory cues and magnetic direction
These are two different problems and popular coverage almost never separates them. A compass tells you which way you are facing. A map tells you where you are. An animal with a perfect compass and no map can hold a heading but cannot correct for being blown off course — and correcting for displacement is the thing that would demonstrate a map.
Navigating animals use several overlapping compasses, not a single magic sense
Established
Specialists would state this without hedging. Multiple independent lines of evidence agree.
Migratory animals orient using redundant mechanisms — sun compasses with circadian time compensation, star patterns, polarised light, olfactory cues and magnetic field direction — with different species weighting them differently and switching when one is unavailable.
Who this applies to
the migratory and homing species in which orientation has been directly tested
Studied in
Danaus plexippus, Caretta caretta, Apis mellifera, Cataglyphis fortis
Why we rate it this way, and what the caveats are
EstablishedHigh confidence
Compass orientation is among the best-replicated findings in animal behaviour, demonstrated independently in insects, birds and reptiles using manipulations that isolate each cue.
How far it can be extended
Assembled from primary work in each species. The claim is about the redundancy of mechanisms across lineages, built only from cases with their own evidence.
Caveats
Knowing which way is north is not knowing where you are — compass and map are different problems.
The mechanism of magnetic detection remains unresolved despite decades of work.
Evidence concentrates in a few well-studied species.
Still unanswered
How is the magnetic field actually detected?
Which animals, if any, have a true positional map?
Menzel et al., 2005 · Proceedings of the National Academy of Sciences
The contested question of whether bees hold a map rather than a set of routes.
Diagram
Two different questions, and only one of them is easy
Schematic. The grid stands for positional information, not a real field map.
The same explanation in words
Two panels side by side. The left, headed "A compass", asks "Which way is south?" and shows a needle in a circle; beneath it, the cues that can supply direction — sun, stars, magnetic field, polarised sky. The right, headed "A map", asks "Where am I now?" and shows a grid of points with one highlighted; beneath it, a note that positional ability has been demonstrated in very few species. A closing line explains the test that separates them: carry an animal sideways off its route, and one with only a compass flies the same bearing into the wrong place, while one with a map turns.
Knowing which way is south does not tell an animal where it is. A compass gives direction; working out position from an unfamiliar place is a separate ability, and far fewer animals have been shown to have it.
Established
Specialists would state this without hedging. Multiple independent lines of evidence agree.
Orientation — maintaining a heading from a directional reference — is mechanistically and evidentially distinct from true navigation, which requires positional information sufficient to compute a course to a goal from an unfamiliar location. Compass mechanisms are demonstrated widely; map-based navigation has been demonstrated in a small number of species by displacement or simulated displacement.
Who this applies to
A distinction in what has been demonstrated, not a claim about which animals possess which ability.
Studied in
Animalia
Why we rate it this way, and what the caveats are
EstablishedHigh confidence
The distinction is not contested among researchers, and the experimental designs that separate the two — displacement, and simulated displacement — are well established.
How far it can be extended
Compass use is shown in birds, insects, turtles and fish; map ability is shown by displacement in a handful of species and assumed in many more.
Caveats
Failing to correct for displacement does not prove an animal has no map: it may lack the relevant experience, or the displacement may exceed the range the map covers.
A "map" in this literature means positional information sufficient to choose a direction. It does not imply a representation resembling a chart.
Still unanswered
What the map is made of in any species where one has been shown — magnetic, olfactory, or a combination — remains open in every case.
Hatchling turtles that have never migrated still swim the right way for where they are
Well supported
Good evidence backs this, though some details remain open.
Loggerhead hatchlings (Caretta caretta) exposed to magnetic fields replicating specific points on their migratory route oriented in directions appropriate to those locations, without prior experience of them.
Who this applies to
loggerhead sea turtle hatchlings, tethered in a laboratory coil system
Studied in
Caretta caretta
Why we rate it this way, and what the caveats are
Well supportedHigh confidence
The animals were naive, which removes learning as an explanation, and orientation tracked the simulated location rather than any fixed direction.
Caveats
Tethered hatchlings in a tank; the available behaviour is constrained.
Shows position-appropriate orientation, not that the animal knows where it is.
Field manipulations are coarser than the gradients a turtle meets in a short journey.
Still unanswered
Is an inherited response set a map, or a very good lookup table?
Places the result in the unresolved map-versus-compass debate.
The turtle result is the strongest single piece of evidence in the map debate, and the reason is that the animals were naive. A hatchling that has never made the journey cannot have learned which way to swim for a magnetic signature it has never met. Whether an inherited set of responses amounts to a map, or to a very good lookup table, is a fair question and an unresolved one.
The sun moves and the stars turn. Both can still be used for direction, and the ways round those two problems are completely different.
A compass has to point at something that stays put. Neither the sun nor the stars do, and the two solutions animals have found are worth comparing because they are not variations on a theme. The sun is dealt with by correction: read its position, then adjust for how far it has moved since dawn, which requires knowing the time. The night sky is dealt with by ignoring almost all of it and attending to the one part that does not move — the point everything rotates around.
How we know
Moving the sun with mirrors, and watching a bird turn
Is a restless caged bird actually using the sun, or merely doing better on sunny days?
Starlings in the season of migratory restlessness were kept in a circular cage from which nothing was visible but the sky, and the direction of their fluttering recorded. Mirrors were then arranged around the cage so that the sun appeared to be in a different part of the sky than it was — deflected by a known angle — while everything else stayed exactly as it had been.
What happened
The birds held a consistent direction under clear sky, shifted their heading by the angle the mirrors had deflected the sun, and lost their directional preference entirely when the sky was fully overcast.
What it shows
That the sun is the reference, and that the birds are reading its position rather than something correlated with sunshine. The deflection is what makes it an experiment: a bird that merely prefers a heading in good weather has demonstrated nothing, and a bird that turns by exactly the angle you moved the sun has demonstrated a sun compass.
What it does not show
It does not show how the bird knows which direction to want, which is a different and much harder question — the compass supplies a bearing, not a destination. It also says nothing about navigation over a real journey: these are caged birds in restlessness, not birds finding anywhere.
The controls — what makes this evidence rather than a story
The same birds tested with and without the mirrors, so each animal is its own comparison.
A cage that hides the horizon and the landscape, leaving the sky as the only reference.
Overcast days recorded as a natural control: with no sun, there should be no consistent direction.
The sun moves, so using it as a compass means knowing the time. Shift an animal’s internal clock by six hours and it sets off about ninety degrees wrong — confidently.
Established
Specialists would state this without hedging. Multiple independent lines of evidence agree.
Sun-compass orientation requires time compensation for solar azimuth change. Animals held under light–dark cycles shifted from local time depart on headings rotated by approximately the angle the sun traverses during the shift, in the predicted direction.
Who this applies to
Demonstrated in homing pigeons and in birds in orientation cages, and separately in insects including monarchs and bees.
Studied in
Columba livia, Aves, Insecta
Why we rate it this way, and what the caveats are
EstablishedHigh confidence
The prediction is quantitative — a specific angle for a specific shift — and it is met. Few results in behavioural biology are that sharp.
How far it can be extended
Clock-shift experiments produce the predicted rotation in birds and in insects, in laboratories on several continents.
Caveats
Clock-shift measures the initial heading; animals frequently correct later using other cues, so a wrong departure is not a failure to get home.
Homing pigeons are domestic birds selected for this behaviour, and the strength of their sun-compass reliance may not be typical.
Still unanswered
How the compass output is weighted against magnetic and landmark information when they disagree.
The same compensation in an insect, with the clock localised to the antennae.
Diagram
Shift the clock, and the heading rotates by a predictable angle
Approximately fifteen degrees per hour of shift — the rate the sun moves.
The same explanation in words
Two circles. In the first, an untreated bird departs on a heading pointing directly at home. In the second, a bird whose internal clock has been shifted by six hours departs on a heading rotated roughly ninety degrees from home, with the angle marked. A closing note states that the bird is not confused but confident, specific, and wrong by exactly the amount the shift predicts.
How we know
Putting a pigeon’s clock six hours wrong
If an animal steers by the sun, it must be correcting for the sun moving. What happens if you break the correction?
Homing pigeons were kept for several days in a room whose lights came on and went off on a schedule shifted by a known number of hours from the world outside — so that the birds’ internal clocks were running fast or slow by that amount. They were then taken away from the loft and released, and the compass bearing they took in the first minutes was recorded and compared with untreated birds released at the same place.
What happened
The shifted birds set off on a heading rotated from the correct one by roughly the angle the sun travels in the period of the shift — about fifteen degrees per hour — and in the direction the shift predicts. Controls departed correctly.
What it shows
That the sun compass is time-compensated, and that the compensation runs off an internal clock rather than off anything in the sky. The quantitative match is what makes it decisive: a confused bird would scatter, and these birds were confident and specific and wrong by the predicted amount.
What it does not show
It does not show that the pigeon fails to get home — most clock-shifted birds correct later, once other information becomes available, which is itself a clue that the sun compass is one input among several. And it says nothing about the map: a bird that departs on a rotated bearing was told which way to fly by the sun, and told where home was by something this experiment never touches.
The controls — what makes this evidence rather than a story
Untreated pigeons released at the same sites on the same days.
A known, deliberate shift, which turns the prediction into a specific angle rather than a vague expectation of confusion.
Initial bearings taken before the birds could use any landmark information from further along the route.
Schematic. Star positions are decorative rather than a real sky.
The same explanation in words
A circular night sky with scattered stars and a marked centre of rotation, with an arc showing the direction everything turns. Beside it, two notes: what a young bird learns is which part of the sky stays still while the rest turns; and why that works — it gives north without recognising any individual star, and it keeps working as the sky slowly changes over millennia. A closing line records that rotating a planetarium sky about a false centre makes the birds orient to the false one.
How we know
Taking the stars away one at a time
Night-migrating birds orient under a starry sky. Are they reading specific constellations, or something more general?
Buntings in orientation funnels — which record attempted direction as ink footprints on sloping paper — were placed under a planetarium sky that could be manipulated in ways no real sky permits. The whole sky could be rotated, individual constellations blanked out, and the axis of rotation moved to an arbitrary star. Crucially, some birds were reared from fledging without ever seeing a rotating sky at all.
What happened
Birds oriented by the region of sky around the axis of rotation rather than by any particular constellation, and rotating the sky rotated their headings. Birds reared without a rotating sky failed to orient by stars at all. Birds reared under a sky turning about an arbitrary star treated that star as the pole.
What it shows
That the star compass is learned in early life from watching the sky turn, and that what is inherited is a procedure — find the still point — rather than a chart. That is a better design than inherited constellations, because precession moves the pole star over millennia while the rule stays correct.
What it does not show
A star compass gives direction and nothing else; it says nothing about how a bird knows where it is. The planetarium sky is brighter and simpler than a real one, and rearing birds without a natural sky is a drastic manipulation with effects beyond the visual. Funnel data are also intentions rather than journeys.
The controls — what makes this evidence rather than a story
Rotating the artificial sky while the room and the magnetic field stayed constant, so a change in heading has one available cause.
Selective removal of individual constellations, distinguishing dependence on a specific pattern from dependence on the rotational axis.
Birds reared without sky rotation, testing whether the compass is inherited or learned.
Birds reared under a sky rotating about a star that is not the pole star, which predicts a specific wrong answer if the compass is learned.
The planetarium result is the one that shows what is actually learned. Young indigo buntings raised under a sky rotating about a false centre took that false centre as north — so the compass is not a memorised pattern of stars but a rule about rotation, learned before the bird ever migrates. It is also a rule that survives the slow drift of the sky over thousands of years, which a memorised pattern would not.
Words used here
Clock shift
Holding an animal under a light–dark cycle offset from local time, so that its internal clock is wrong by a known amount. The standard test for a time-compensated sun compass.
Almost everything known about maps comes from moving an animal somewhere it did not choose to be.
A bird released at home and arriving at its wintering ground has demonstrated nothing about maps: a fixed inherited heading would have done the same job. The question only becomes answerable if you move the animal off its route first. Then the two possibilities predict visibly different things — a compass-follower carries on along its original bearing, and a map-user turns.
Diagram
Same displacement, same species, opposite answers
Schematic. Geography is illustrative rather than a map.
The same explanation in words
A bird is caught on migration at one point, carried by aeroplane to a release site well to one side of its route, and released. From that release point two tracks diverge: adults turn towards the usual wintering range, while first-year birds continue on the heading they held before capture and miss it. A closing note observes that this is one species containing both a map-user and a compass-follower, sorted by experience.
How we know
Moving eleven thousand starlings to see what they would do
Is migration one ability or several? Specifically: does a bird know where it is, or only which way to fly?
Starlings were trapped in the Netherlands during autumn migration, ringed, transported several hundred kilometres south to Switzerland, and released — a place none of them had any business being. The crucial element is that recoveries were analysed separately by age. Juveniles had never migrated; adults had made the journey at least once. If migration were a single inherited programme, both groups should behave identically.
What happened
Juveniles continued on the original compass heading from the displaced release point and were recovered in Spain, well outside the species’ normal wintering range. Adults changed heading and were recovered in their usual wintering areas in northern France and Britain.
What it shows
That "migration instinct" is at least two capabilities. A young bird inherits a direction and roughly how long to hold it, which works from the place it was born and fails predictably from anywhere else. An experienced bird knows its position relative to a goal — true navigation — and that is learned rather than inherited.
What it does not show
It does not reveal what the adults use to work out where they are; the map component is demonstrated here and identified nowhere. Recovery data are also biased by where people are and how likely they are to report a ring, which distorts distributions in ways that cannot be fully corrected. And displacement is a severe manipulation — the birds arrive in poor condition in an unfamiliar place, and motivation cannot be measured.
The controls — what makes this evidence rather than a story
Age determined from plumage at ringing, so the two groups are separated before anyone knows what will happen.
A very large sample — more than eleven thousand birds — because recovery rates for ringed birds are low and the result depends on the shape of a distribution.
Birds trapped mid-migration rather than at the breeding site, so all were already in migratory condition.
Recoveries reported independently by finders across several countries, with no involvement from the experimenters in where birds turned up.
Carry a migrating bird a thousand kilometres sideways and what happens next depends on its age. Adults turn towards where they were going. Birds on their first migration carry on as though nothing had happened.
Established
Specialists would state this without hedging. Multiple independent lines of evidence agree.
In displacement experiments on several migratory passerines, experienced adults compensate for displacement and orient towards the normal wintering area, while first-year birds maintain the compass heading held before capture, indicating that route experience is what converts compass orientation into map-based navigation.
Who this applies to
Demonstrated in starlings, chaffinches and white-crowned sparrows; the age split is the general result.
Studied in
Passeriformes
Why we rate it this way, and what the caveats are
EstablishedHigh confidence
Two independent methods, decades apart, on different species and flyways, producing the same age split.
How far it can be extended
Reproduced with ringing recoveries in the 1950s and with radio telemetry fifty years later, in different species on different continents.
Caveats
Ringing recoveries depend on birds being found and reported, which varies by country and by habitat.
Telemetry samples are necessarily small, and follow birds for days rather than to their destination.
Species that migrate socially may acquire the correction differently, from companions rather than from their own experience.
Still unanswered
What experienced birds are actually reading to establish position, which remains unresolved for every species tested.
Eleven thousand starlings displaced to Switzerland: adults reached the normal wintering area, juveniles ended up parallel to it and in the wrong place.
Thorup et al., 2007 · Proceedings of the National Academy of Sciences
The same split, watched directly: birds displaced across a continent and followed by aircraft.
How we know
Flying sparrows across a continent and following them by aeroplane
Does a migrating bird know where it is, or only which way it was going? And does the answer depend on age?
White-crowned sparrows were caught on migration in Washington State, in the north-west of the United States, and flown to New Jersey on the other side of the continent — a displacement of some three and a half thousand kilometres, sideways relative to their route. Adults and first-year birds were released together, each carrying a radio transmitter, and followed from a light aircraft to record the direction each actually took.
What happened
The adults turned and headed towards their normal wintering range in the south-west. The first-year birds continued on the heading they had been flying before capture, as though nothing had happened.
What it shows
That experienced birds have positional information covering a continent — a map — and that inexperienced birds do not, running instead on an inherited compass bearing. It is one species containing both kinds of navigator, sorted by whether they have made the journey before.
What it does not show
It does not show what the map is made of: magnetic, olfactory, celestial or some combination, all remain possible after this result. Samples are small, because following birds from an aircraft is expensive, and the tracking covers days rather than the whole journey.
The controls — what makes this evidence rather than a story
Adults and juveniles displaced identically and released together, so the comparison is age and nothing else.
Birds caught mid-migration rather than at a breeding site, so all were actively travelling.
Direct tracking rather than recovery, so the bearing is measured rather than inferred from where a bird later turned up.
The strongest version of the design does not move the animal at all. If the magnetic field is what carries position, then reproducing the field of a distant place around a stationary bird should make it behave as though it had been carried there — and in adult reed warblers, it does.
How we know
Moving the magnetic field instead of the bird
If a bird corrects for being carried a thousand kilometres, is the magnetic field enough on its own to tell it that it has been?
Adult reed warblers were tested in orientation cages placed inside large coil systems. The coils reproduced the magnetic intensity and inclination of a site roughly a thousand kilometres to the east, while the birds remained physically where they were — same place, same sky, same smells, same time. Their headings were compared with those of birds tested in the local, unaltered field.
What happened
Birds in the shifted field changed their headings in the direction that would compensate for the displacement the field implied. Birds in the local field did not.
What it shows
That magnetic information alone can carry position, not just direction — a magnetic map. Because nothing moved, the result cannot be explained by anything the journey itself might have supplied.
What it does not show
It does not show which magnetic parameter the birds read, and it does not extend to inexperienced birds, which do not compensate. As with every cage study, the measurement is an intended heading rather than a journey completed.
The controls — what makes this evidence rather than a story
Birds tested in the true local field in the same cages and coils, with the coils energised but set to local values.
Everything except the magnetic field held constant, which is what makes this a virtual rather than a real displacement.
Adults with previous migratory experience, tested during the migratory season.
Change only the magnetic field around an adult migrant — leaving it exactly where it is — and it shifts its heading as though it had been carried to the place that field belongs to.
Well supported
Good evidence backs this, though some details remain open.
Adult Eurasian reed warblers tested in orientation cages within coil systems reproducing the geomagnetic parameters of a site approximately a thousand kilometres away altered their headings in the direction that would compensate for that displacement, indicating that magnetic parameters alone can supply positional information to an experienced migrant.
Who this applies to
Adult reed warblers with previous migratory experience, in one population.
Studied in
Acrocephalus scirpaceus
Why we rate it this way, and what the caveats are
Well supportedHigh confidence
An unusually clean design — nothing moved but the field — with a result in the predicted direction. The limits are of scope rather than of quality.
How far it can be extended
The virtual-displacement design has been run in few species, and a magnetic map should not be assumed in animals where it has not been tested.
Caveats
Adults only: first-year birds tested the same way do not compensate.
Cage headings are an intention, not a journey.
What the birds read from the field — inclination, intensity, or both — is not established by this design.
Still unanswered
Whether the same ability exists in the many migrants that have never been tested this way.
Which one dominates depends on conditions, experience and what is available.
The same explanation in words
Five layers listed in order. Landmarks and remembered routes, used close to home once the ground is familiar. Path integration, a running vector computed from the animal’s own movement. Sun and star compasses, which give direction and both need a clock. The magnetic field, which gives direction almost anywhere and position only rarely. And smell, which covers the last stretch and possibly more. A closing note explains that removing any one of them usually leaves the animal still able to arrive, which is exactly what makes any single cue hard to prove.
The redundancy is why this field is so hard to do experiments in. Block one cue and the animal generally still gets there, which produces a null result that means nothing — not "this cue is unimportant" but "the others covered for it". The informative designs are the ones that make cues disagree rather than removing them: rotate the polarised sky while leaving the sun visible, or shift the clock while leaving the landscape alone, and see which the animal believes.
Calibration between the systems is the other half of it. A magnetic compass and a star compass can drift apart — magnetic north is not celestial north, and the difference varies across the planet — so migrants appear to re-set one against the other, most often around sunset. Which is the reference and which gets adjusted is not settled, and may differ between species.
Why it matters: Magnetic orientation is well demonstrated and the receptor is not identified. It is one of the longest-standing unsolved problems in sensory biology.
What would settle it: Identification of a receptor whose disruption removes the behaviour without removing anything else.
Does any animal have a true positional map?
Why it matters: It is the difference between following a heading and knowing where you are — and it is asserted far more often than it is demonstrated.
What would settle it: Displacement experiments where an animal corrects for a movement it could not have detected.
How do multi-generational migrations work?
Why it matters: No individual monarch completes the round trip, so whatever guides the route cannot be individual memory.
What would settle it: A mechanism linking inherited orientation preferences to specific overwintering sites.
How complete this page is, and what it is still missing
NatureHQ publishes its own gaps. This page is at 77% completeness against what we would call a finished subject, and was last reviewed on 2026-09-03. It carries 28 claims and answers 20 mapped search questions.
1 high-priority search intent(s) not yet covered
no research from the last few years is attached — check for newer work
no popular claim about this subject has been checked yet
Bird migration — by far the most-searched navigation topic — has no primary research attached yet.
Star compasses and polarised-light orientation are named but not evidenced.
The radical-pair hypothesis is referenced without being explained.