Emlen funnel

An Emlen funnel is a bird cage shaped like an inverted cone, used to study bird behaviour, in particular birds' migratory instincts. An ink pad is placed on the bottom, so when the bird hops or flutters onto the sloping walls it leaves a track before slipping back down again. The bird's view through the top of the cage can be manipulated, for example to example how it responds to different apparent "star patterns" (actually generated in a planetarium).

References

*"Migration" by Hugh Dingle, page 88.