I work with a shorebird expert who has been tracking migrations (Latham snipe whose range extends from Russia/Northern Japan to Southern Australia).
I think an early technique of tracking their migration before gps/chip/batteries were small enough was a primitive light sensor + data logger that would log day/night hours on the bird as it flew from island to island and the light data was enough to roughly estimate lattitute (and often enough to infer a location/date.
The data looked great in this form. It wasn't hourglass but with jagged edges and shifts. You could easily see which months the bird stayed in a single place for several days etc. clever stuff.
nice. had no idea about that connnotation :) ... goes with black swan event as a saying that's ill fitting for these parts (in southern Australia all we have are black swans).
