Hey! Somebody else had a comment about bird migration, so I have an excuse to write more about it. And this time, I get to use the term "testicular diameter."
Dave brought up the fact that they are said to have actual magnets near their beaks, and that's true too. They have very small crystals of a mineral called magnetite, which is a type of iron oxide. The current thinking is that it is a different system, which gives the bird information about the strength of the local magnetic field, more like a magnetometer, rather than a compass. It is thought that the birds can use this sense to form a map of the magnetic environment and it can help them find their way around places they've been before, like how some animals can explore and learn where they are based on odors and gradual variations in types of vegetation. It has been calculated that with the sensitivity of this organ, they can recognize locations they've been before to within a few 10's of kilometers.
And he brings up another cool fact, about how they know to go North at one time of year and South at another. No one can explain how that happens, but it's clear that it isn't learned from older birds, they know it instinctively. In fact, you can fool them, by artificially controlling the light/dark cycle to make them think that it is winter, and they will begin to put on weight, and the males will experience an increase in testicular diameter in preparation for the breeding season, and they will show migratory restlessness, trying to go South. Even a caged bird will spend more time at the South end of the cage!
Anybody else want to talk about migratory birds? How about single domain and/or paramagnetic particles? How about learning and computation in the brain? Anyone? I can talk about the proteins that underlie electrical activity in the brain too.
I wonder how many extra hits I will get now that I mentioned "testicular diameter."
Anyway, I gotta go.