Day 2: the square eggs of Gerard Baerends
Gerard Baerends was a Dutch biologist, who conducted a behavioral study of herring gulls in 1951.
In Baerends’ experiments, two experimenters walked into the colony, which caused the birds to leave their nests. One nest was chosen for study and two of its three eggs were removed. These eggs were replaced by two model eggs. The model eggs were not placed in the nest cup, but were placed instead on the rim of the nest. One of the experimenters then hid in a small portable tent that was set up near the chosen nest, and the other experimenter left the colony. The nest owner soon returned, and the experimenter in the tent could easily observe and record the behavior of the returning bird. Typically, the gull would enter the nest and sit on the one egg. It would then rise, look at the model eggs on the nest rim, retrieve one egg and then retrieve the other.
… The results of these experiments showed that some aspects of the stimulus were not very important for the gull. Shape, for example, had relatively little effect… round, square, oblong, and egg-shaped models were retrieved with about equal frequency.
Jerry A. Hogan The Study of Behavior: Organization Methods and Principles, 2017
Life Magazine ran a feature about Baerends’ gull study in 1955. (Most of these photos are from that issue.)
For their table of contents, Life’s “Science” editor gave the article the factually correct title, Wooden eggs test a herring gull’s instincts. By the end of the article, however, the magazine shifted its focus and it became all about the square egg…
An Irresistible Square Egg
… Professor Baerends made the wooden egg experiment this year on Terschelling Island in the North Sea. His experiments have taught him other things about herring gulls. To fool them he made eggs of different shapes and colors… and placed some of them on the edge of a nest and waited to see which the gull would drag in. Herring gulls, he found, are usually bored by plain eggs. But if the egg is speckled, the bird will try to hatch it, even when it is square (next page).
Yes. Clearly, square eggs are irresistible. To magazine editors, at least.
Baerends was a professor at the University of Groningen. And so the university’s museum now holds Baerends’ eggs in its collection.
Note: As recently as 3 years ago, scientists conducting a bird behavior experiment also used a decoy square egg. As evidenced in the photos below. from a 2017 study entitled, Context-dependent response to eggs: egg retrieval versus egg rejection in a conspecific brood parasite.