I'm reading the article and it strikes me that the birds might have a very accurate biological clock allowing east/west localization. I sometimes know just when

I'm reading the article and it strikes me that the birds might have a very accurate biological clock allowing east/west localization. I sometimes know just when the sun will rise or set, and a few minutes difference from that expected time, let alone a half hour or more, could tell me if I were east or west. Think jet lag, but millions of years of evolution have turned it into something more accurate for migratory animals. North/south may be temperature or the angle of the sun versus where they expect it. Once again, millions of years may have given birds a more precise feeling for exactly how high the sun should be. You'd have to watch the birds for better homing ability when the sun is visible vs when completely cloudy. It could be interesting to see how well they home if released at different times of the day, or different seasons. I'm interested in the actual data that has been gathered.