Study

A technique for recording migratory orientation of captive birds

Emlen, Stephen T.; Emlen, John T.

The Auk, 1966

Peer-reviewedcontrolled laboratory experimentcaptive

What they did

A caged bird cannot migrate, so the problem is measuring which way it wants to go. The apparatus is a funnel with an inked pad at the base and blotting paper forming the sloping walls: a bird in migratory restlessness hops upwards repeatedly and leaves a scatter of footprints, densest in the direction it is attempting. The paper is then read as a distribution of headings.

Studied in: Passerina cyanea
Sample size: indigo buntings across repeated orientation trials

What they found

The funnel produced repeatable directional records from individual birds, with scatter concentrated in the seasonally appropriate migratory direction, and allowed the sky, magnetic field or timing to be manipulated while the bird’s response was measured.

What it means

The authors' reading, and ours. Where they differ, that difference is the point.

How the authors put it

Migratory orientation can be measured quantitatively in captivity, opening the mechanism to experiment rather than inference from ringing recoveries.

How NatureHQ reads it

It is worth dwelling on how much of migration research this one piece of blotting paper made possible. Before it, the evidence was almost entirely correlational — a ring put on here, a bird found there. Afterwards you could take the stars away, rotate a magnetic field, shift a bird’s internal clock, and watch which way it tried to go. Almost every classic migration experiment since is a variation on filling in this funnel.

Limitations

Measures intention in a cage, not the route a free bird flies.
Migratory restlessness is a captive phenomenon whose relationship to real departure decisions is not exact.
Scatter is often wide, so conclusions rest on averaging across many trials and birds.