How homing pigeons find their way home

How does the bird know where home is?

A pigeon can be transported hundreds of kilometers in a covered cage, released somewhere unfamiliar, and choose a fairly accurate direction home within a minute. It hasn't simply watched the scenery go past. What information is it using?

The first paragraph gives us two main possibilities. The pigeon might keep track of the trip: which direction it moved, how far, and when it turned. Alternatively, it might have a map sense that lets it work out its position relative to home after arriving somewhere new. Think of the difference between remembering the turns you took and locating yourself on a map. That's an analogy, not a claim that the bird has a literal navigation app.

The route-tracking explanation may be easier to picture. But finding an explanation easy to imagine doesn't make it right. Paragraph 2 tells us that this first alternative “seems unlikely,” so we need to see why.

One proposed system uses an internal magnetic compass. If that is how the bird tracks its journey, interfering with the magnetic information should create trouble. Yet magnets and artificial magnetic fields only occasionally affect the birds. That weakens this particular model. It doesn't, by itself, eliminate every possible way of tracking movement.

The next model involves monitoring movement more directly: turns, acceleration, slowing down, and the time spent on different parts of the trip. Constant rotation or complete anesthesia should interfere with that sort of conscious tracking. But the described treatments don't impair orientation.

There's still a qualification. Nobody has tried all the listed disruptions together—darkness, anesthesia, rotation, and a reversed magnetic field. Why might that matter? If the birds have more than one source of information, disabling one could leave another available. The proposed combined experiment would address that possibility. So the evidence makes route tracking look unlikely; it hasn't conclusively eliminated it.

Paragraph 3 calls the map sense “more promising,” but immediately admits that its nature is mysterious. We now have a favored general explanation, not a solved mechanism.

Papi proposes a map based on smell. The birds learn to associate odors arriving on the wind with the directions those odors come from. Over time, that could give them a map of their surroundings. Smelling the air while being transported or after release would then help them work out the direction of home. The proposal is more specific than saying pigeons have a good nose: they would use smells as directional information.

Papi's nostril-plugging experiments initially look supportive. The birds orient poorly and return slowly. But is that because they can't smell, or because having their nostrils blocked distracts and distresses them? We need a way to separate those possibilities.

The final paragraph supplies several problems for the smell account. Schmidt-Koenig and Phillips couldn't detect an ability to distinguish ordinary air from filtered air. If natural air carries the map information, that missing distinction is a problem. It isn't a claim that pigeons can never detect any odor.

Then come tests that address our concern about discomfort. Nasal tubes bypass the smell-sensing chamber while allowing comfortable breathing; the birds remain oriented. Spraying the smell-detecting tissue with anesthetic also leaves orientation normal. Those results separate blocking smell from the distress of plugging the nostrils, and they make Papi's interpretation much less convincing.

We finish without a full answer to our opening question. The writer favors a map sense, but the proposed smell mechanism hasn't held up. Our main point should include that judgment and the remaining uncertainty, not just list the two possible explanations.