The Greylag Goose


The greylag goose retrieving its egg

Another example of an action pattern triggered by a sign stimulus appears in so many textbooks it might be called the Pavlov's Dog of ethology. This is the greylag goose retrieving her egg. The example comes from Lorenz and Tinbergen (1938).

How does the greylag goose retrieve her egg?

The sight of an egg outside of the nest sets off egg-retrieval. When a human puts an egg near the nest, the greylag goose sees it but does not immediately reach for it. She does a "double take." She looks away from it and then looks back. Next she moves her head back and forth toward the egg in several short, quick movements. Then she extends her neck as far as it will go-quite far, in a goose-and moves toward the egg with her neck fully extended, using a curious low-to-the-ground waddle unique to this situation.

When the bottom of her beak touches the egg, the goose's neck muscles quiver with tension and slowly she contracts her neck, rolling the egg back toward the nest. The egg, being egg-shaped, tends to roll off to one side or another. The goose moves her beak from side to side, keeping the errant egg on course. If it eludes her, she returns to the nest, spots the egg still lying outside the nest, and repeats the whole movement (Bermant & Alcock, 1973).

What is endogenous running-out?

Lorenz found that if he removed the egg while the mother bird reached for it, the bird nevertheless went through the entire action of retrieving the egg, as if retrieving an imaginary egg. This led Lorenz to formulate the concept of endogenous running-out. Endogenous means coming from within. Once the action pattern was set off by a sign stimulus, the motor program kept running to its conclusion, even if the egg had rolled off to the side.

If we accept Manning's (1972) view that reflexes are good examples of motor programs or action patterns, there are abundant examples of endogenous running-out in human action patterns. Vomiting, for instance, has an all-or-none character. One can hold it off for a while, but once the activity starts, one is forced to carry it through to completion. Many but not all action patterns have this characteristic of endogenous running-out.


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Copyright © 2007 Russ Dewey