Dizzy pigeons

image from flickr
text from Stuff.co.nz
'A New Zealand scientist has used a peculiar glitch in the Earth's magnetic field at Mt Roskill here? to demonstrate how pigeons, dropped off hundreds of kilometres from home, are able to navigate back to their lofts.

"We are now confident that pigeons do use the intensity of the Earth's magnetic field to determine position during homing," Todd Dennis of Auckland University said today.

He led research published today in the Proceedings of the Royal Society which shows homing pigeons use the strength of the Earth's magnetic field to sense how the field around them is changing and work out where they are relative to home. Dr Dennis released homing pigeons in New Zealand's own "X-files" spot – the Auckland Junction Magnetic Anomaly, an area of New Zealand where the Earth's magnetic field is naturally distorted – to test whether the anomaly confused the birds' ability to position themselves, the Guardian newspaper in Britain reported. A cluster of massive rock slabs deep below the surface causes a detectable spike in the geomagnetic field. On release, the birds flew up to 4km in the wrong direction, parallel or at right angles to variations in strength of the local magnetic field, before redirecting themselves towards their loft.

To track the pigeons on release, the researchers fitted them with tiny global positioning system (GPS) devices, and found that the geomagnetic anomaly threw the birds for a loop. Of the 92 pigeons released around the anomaly, 59 clearly flew relative to the direction of the local magnetic field – not the Earth's field. As soon as they escaped the bounds of the anomaly, the pigeons corrected their direction and headed directly home. Dr Dennis said this showed the birds kept track of gradients in the magnetic field to navigate.

This discovery will settle a long-running debate over whether pigeons navigate by smell or through an ability to read Earth's magnetic fields. Some birds are known to use the sun as their predominant compass, and migratory birds that fly at night are known to navigate by stars, but their use of magnetic fields has proved harder to unravel.

In 2004, other scientists at the university showed pigeons were capable of using the same magnetic "sixth sense" as fish to find their way home: tiny deposits of a mineral called magnetite, or lodestone, in their beaks. The mineral is in the same part of the body, and uses the same nerve to connect to the brain, as in trout, stingrays and a bird called the bobolink.

Power requirements for occupying virtual space

An avatar in Second Life does have a footprint, in fact quite a large one.

the following is from http://www.roughtype.com/archives/2006/12/avatars_consume.php

Philip Rosedale, the head of Linden Lab, the company behind the virtual world: "We're running at full power all the time, so we consume an enormous amount of electrical power in co-location facilities [where they house their 4,000 server computers] ... We're running out of power for the square feet of rack space that we've got machines in. We can't for example use [blade] servers right now because they would simply require more electricity than you could get for the floor space they occupy."
...
If there are on average between 10,000 and 15,000 avatars "living" in Second Life at any point, that means the world has a population of about 12,500. Supporting those 12,500 avatars requires 4,000 servers as well as the 12,500 PCs the avatars' physical alter egos are using. Conservatively, a PC consumes 120 watts and a server consumes 200 watts. Throw in another 50 watts per server for data-center air conditioning. So, on a daily basis, overall Second Life power consumption equals:

(4,000 x 250 x 24) + (12,500 x 120 x 24) = 60,000,000 watt-hours or 60,000 kilowatt-hours

Per capita, that's:

60,000 / 12,500 = 4.8 kWh

Which, annualized, gives us 1,752 kWh. So an avatar consumes 1,752 kWh per year. By comparison, the average human, on a worldwide basis, consumes 2,436 kWh per year. So there you have it: an avatar consumes a bit less energy than a real person, though they're in the same ballpark.

Which means, in turn, that avatars aren't quite as intangible as they seem. They don't have bodies, but they do leave footprints.