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A guided journey · 5 stops

How a bird finds Africa

A warbler hatched in a Surrey hedge, alone, at night, arriving somewhere it has never been. Four things have to be true for that to work, and one of them was not established until 2015.

The route

  1. Bird migration
  2. Animal navigation
  3. Magnetoreception
  4. Migration
  5. How we know where animals go

The problem is worth stating properly before any of the answers, because the popular version of it is too easy. A young warbler leaves in its first autumn without its parents, at night, and reaches a wintering area in Africa it has never seen. It is not following anybody. It has no map of Europe. And it is going somewhere specific enough that it will come back to roughly the same place the following year.

The temptation is to answer "instinct" and stop. What that word covers is a compass bearing and a duration — a rule, not a route — and a rule can be wrong for the place an animal finds itself in. This route follows what the rule can do, where it fails, and what replaces it once a bird has made the journey once.

The order runs from the thing that is inherited to the thing that has to be learned, and ends with the instruments that let anybody check.

  1. Stop 1 of 5. Birds

    Start with what the bird is actually carrying

    Cross-breeding blackcaps that migrate in different directions produces offspring that head between the two — so the direction is inherited, and inherited as a quantitative bearing rather than as a route. That is the foundation for everything after it, and it is also the limit: a bearing is a rule, and the same rule that works from a Surrey hedge takes a displaced bird into the wrong continent.

    Read Bird migrationMove a young bird 500 km and it flies the same heading into the wrong country. Move an adult and it corrects.

  2. Stop 2 of 5. Senses and abilities

    Then the compasses, and why there are three of them

    A bearing is useless without something to measure it against, and migrants carry sun, star and magnetic compasses at once. This page is where the three are set beside each other — including why the sun compass needs a clock, and what a bird does when two compasses disagree. Read after the inherited bearing, the redundancy stops looking like overkill and starts looking like insurance.

    Read Animal navigationA butterfly’s navigational clock is not in its brain. It is in its antennae.

  3. Stop 3 of 5. Senses and abilities

    The compass that works when the sky does not

    The magnetic compass is the one that survives cloud, and it is also the one whose mechanism is still missing after half a century — a rare combination of a settled behaviour and an unsettled cause. It belongs here rather than earlier because its most interesting property only matters once you have met the others: it reads the angle of the field lines rather than which end is north, which is why a bird carried across the magnetic equator behaves as though its compass has inverted.

    Read MagnetoreceptionA bird’s magnetic compass has been demonstrated for fifty years, in laboratories all over the world. Nobody has found the receptor.

  4. Stop 4 of 5. Behaviour and cognition

    The journey as an energy problem

    Knowing the way is not the hard part of getting to Africa. Fuelling is: birds roughly double their mass before a long crossing, and some shrink their digestive organs to save weight. This is also where stopovers stop being rest stops and become the reason a flyway exists — a stretch of mudflat used for three weeks a year can be the thing the whole route depends on.

    Read MigrationA migrating animal is one that has switched off the responses that would normally make it stop. That, and not distance, is what makes a journey a migration.

  5. Stop 5 of 5. Senses and abilities

    And how anybody knows any of this

    Every claim on this route came from an instrument, and each instrument has a blind spot worth knowing. A ring gives two dots and a guess in between. A geolocator gives a route and only from birds that survived to be caught again. Radar counts what is aloft tonight and cannot name a single species. Ending here turns the preceding pages from assertions into measurements with known limits.

    Read How we know where animals goA ring gives you two dots on a map and nothing in between. Everything since has been an argument about how to fill in the middle.

Where this leaves you

You end able to say what a first-year bird has and what it lacks. It has a heading, a duration, and at least three compasses that cross-check each other. It does not have a map: displaced sideways, it flies the inherited bearing anyway and winters in the wrong country, which is exactly what eleven thousand ringed starlings did in 1958.

What the route does not settle is what the map is made of in the birds that have one. Magnetic parameters are the best-supported candidate, and after fifty years nobody has found the receptor that would read them.

Last reviewed 2026-09-03. All guided journeys