Emlen 1970 · indigo bunting · star rotation detection · critical period
A young indigo bunting learns north by watching the night sky rotate. It doesn't memorize star positions — it detects the rotation axis: the still center of a turning system. After roughly fourteen nights, the compass is set. Change which point the sky rotates around, and the bird calibrates to that point instead. The specific stars don't matter. The axis does.
conditionspeed
nights: 0
frames: 0
mode: normal
stars: 150
press start to begin — trails accumulate across nights
What it can't show: the simulation represents the rotation detection problem geometrically but not neurologically. Real buntings likely use a two-stage process — a visual motion system that extracts star positions, feeding into a developing magnetic/celestial compass integration system. The exact neural mechanism that detects the low-motion region and converts it into a directional anchor is unknown. The critical period closure — whatever stops the compass updating after calibration — is also unknown. The simulation shows the information that must be available; it does not show how the bird extracts it. There is a further gap the simulation cannot bridge: what it is like to learn north, if it is like anything at all.