How migrating birds keep course when landmarks vanish

Which cue fits best when the landscape is no help?

Pick the case that best matches the evidence. Different species solved the 'no landmarks' problem in different ways, so this is a comparison of documented situations rather than a universal rule.

Reed warbler in a virtual magnetic displacement experiment

This case supports a magnetic map-like cue. In reed warblers, successful re-orientation in the experiment depended on trigeminal input, suggesting positional magnetic information mattered.

Mediterranean shearwater over pelagic water

This case points most strongly to smell, with topography as help when available. In that study, olfactory deprivation impaired navigation, while magnetic disturbance did not produce the same effect.

Lesser black-backed gull after displacement

This case also supports an olfactory contribution. Gulls with intact olfactory nerves compensated better than birds whose olfactory nerves were cut.

These results come from different species and experimental designs. They show that cue use is context-dependent, not that one cue always replaces landmarks.

Birds use both a compass and a map

A useful distinction is direction versus position. A compass tells a bird which way to go; a map helps it estimate where it is. Reviews of migration research argue that long-distance navigation cannot be reduced to landmarks alone. Birds may combine celestial cues, magnetic direction, smell, topography, and experience, switching emphasis when one source becomes unreliable or unavailable.

Is the magnetic sense just one single system?

What happens after birds are displaced?

Common cuckoos

showed compensatory movements toward population-specific staging areas, supporting true navigation beyond simple landmark-following or fixed-vector travel

White-throated sparrows

did not show clear goal-ward compensation after cross-continental displacement; a constant-vector strategy was proposed as one interpretation rather than confirmed as the sole mechanism

General lesson

experienced migrants are not all equivalent: some appear able to correct position, while others may not compensate in the same way under displacement

Displacement studies are a key test because they ask whether a bird can adjust from an unexpected place. The answer varies by species, which is why researchers favor a flexible, multisensory model rather than a single navigation rule.