Question of the Week

Are birds confused by steel in ships?

Sun, 24th Jan 2010

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Captain Jan, Norwich asked:

Hi, Naked Scientists. I'm Jan from Norwich and I'm the Captain of a large oil tanker. I have a question about pigeons. We often get flocks of wild amazing pigeons land on our decks and they just stay for weeks until the crew fatten them up for the pot that is. My question is this: Does the steel in the structure of the ship which is about 50,000 tons affect the pigeons’ navigation system? I've heard that they rely, in parts, on the earth’s magnetic field.


We put this question to Michael Brooke, from the Department of Zoology at Cambridge University and curator of birds in their museum:

I think that’s fairly unlikely, even if it was migrating, crossing the sea in conditions where it was using the magnetic compass.  The distance over which a ship would cause distortion of that compass would really be pretty tiny.  A Feral Pigeon or Rock DoveIn my guess and it is a guess, it would be over maybe a maximum of 100 meters.  And therefore, on that basis, the bird wouldn’t have been pulled off course by the tanker.  Much more a case of the bird feeling knackered, seeing a ship and then landing on the ship.  So I guess, once aboard a ship, a pigeon might be more or less inclined to leave, depending on various factors.  So, some of the factors could be the extent to which it has exhausted its fat - its fuel reserves.  Obviously also another factor would be whether the crew were feeding it and if it was a time of year when the species was naturally migrating, that would put it in a mindset to press on, regardless.  Domestic pigeons that we see around Britain derive from the wild species, a rock dove, but it’s now very difficult to establish what is the natural distribution of rock doves because rock doves have interbred with the domestic pigeons.  Those domestic pigeons have been shifted around the world by people.  So, now you can encounter them in most continents.   On the more distant continents, like Australia and New Zealand, we can be sure they have been introduced by man, but for example South East Asia, there may be a degree of uncertainty.


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Surely the effect of a metal ship, relative to the magnitude of the Earth, would be (scuse the pun) a drop in the ocean as far as the magnetic field goes?

Presumably the birds quite like the safe (relatively) warm resting place and (apparently) friendly crew and so they stay.

Chris chris, Thu, 21st Jan 2010

If I remember correctly, birds do have some sort of built in compass, or at least some do, so it's possible a large amount of steel could confuse them. In particular, I think this would apply to swallows who have been swallowing too many magnets at a time. Geezer, Thu, 21st Jan 2010

I would agree with both your points.

If these birds are coming aboard while the ship is in dock, or not far off the coast, and finding something worth staying on board for (perhaps cook throws a few titbit's for the purpose, to give him a supply of fresh meat later on the voyage), they might be reluctant to leave when, upon taking off, land is no longer in sight.

I believe birds were used for the purpose of leading ships to land, in far off days. Birds would be released and if they returned to the ship, land was not in sight, but if they flew off, the captain had only to follow them to reach land. Don_1, Sat, 23rd Jan 2010

would following a ship have any effect reduced wind resistance, the opertunity to have a rest in t he middle of the sea, a snake left over by the crew, it makes sence to follow the ship... if its going in your direction geo driver, Tue, 26th Jan 2010

Sensors that determine the orientation of the drill string when  drilling directional wells must be set in a non-magnetic length of pipe to avoid magnetic interference. This would be of the order of ten metres above and below the sensor. The Earth's magnetic field is not strong.

So by comparison I would expect that the sensing mechanism of pigeon would be upset by a 50,000 ton tanker. On the other hand some birds - perhaps pigeons - also use stars for navigation and they can certainly use the sun during the day, so they ought to be able to fall back on these alternatives. Ophiolite, Tue, 26th Jan 2010

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