The story of supernormal stimuli begins with the Dutch biologist Nikolaas Tinbergen. As a boy growing up in The Hague in the 1910s, Tinbergen was fascinated by the fish and fowl inhabiting the little pond in his backyard. These early encounters with the wildlife of the Netherlands informed his later work, and as an adult, he kept an aquarium in his home.

One day he noticed that the male three-spined sticklebacks—which have “gorgeous nuptial colors,” Tinbergen observed, “red on the throat and breast, greenish-blue on the back”—went into attack mode every time a red postal van parked outside. They dropped their heads and raised their dorsal fins, a posture normally assumed only in the presence of a rival male.

Wondering whether the fish were reacting to the postal van, Tinbergen introduced variously colored objects into the tank. He discovered that the males became aggressive in response to anything red—the unmistakable sign of another male’s presence—regardless of whether it resembled a fish. The observation sparked Tinbergen’s discovery of color’s influence on animal behavior, for which he shared the Nobel Prize in Physiology or Medicine in 1973.

When he wasn’t observing three-spined sticklebacks, Tinbergen spent a lot of time with adult herring-gull hens, which have pronounced orange spots on their lower mandibles. For the first few weeks of a chick’s life, its mother’s beak is its sole food source. That orange spot is a good target for chicks to aim at when they peck at their mother to prompt her to regurgitate food.

Tinbergen noticed that the chicks in his lab, like the male sticklebacks in his aquarium, aggressively pecked not just at their mother’s beak but at anything with an orange spot on it. It occurred to him that it might be possible to one-up nature, to “make a dummy that would stimulate the chick still more than the natural object,” he wrote.

So Tinbergen started making “super-gulls”: cobbled-together constructions that amplified the orange spot to which the chicks so enthusiastically responded. He painted orange spots on everything from old pieces of wood to kitchen utensils. He made the orange spots bigger and surrounded them with white rings to enhance the contrast. The chicks pecked at absolutely everything that had an orange spot on it. The bigger the spot, the more aggressively the chicks pecked.

Tinbergen called his exaggerated orange spots “supernormal stimuli,” which, he concluded, “offer stimulus situations that are even more effective than the natural situation.” This response to supernormal stimuli is not limited to herring gulls. Chicks from all species will beg for food from a fake bill if it has more dramatic markings than its parents have, and parents will ignore their own eggs and attempt to incubate much larger objects—including volleyballs—if those objects are decorated to resemble eggs.