Observant biologists have long known that among such game birds as quail, partridge, pheasant and grouse, all the eggs in a nest tend to hatch at about the same time—even though they were laid several hours apart. The value of the phenomenon seems obvious: it enables the mother bird to leave the nest for food and protect her brood without worrying about any unhatched eggs. But how is the hatching synchronization achieved? No one has known. Now it appears that scientists were simply not listening hard enough to hear the obvious answer.
Working with nests of quail eggs, Cambridge University Research Psychologist Margaret Vince used sensitive instruments to record the movements and sounds of quail embryos during the last three days of their incubation period. Some twelve to 18 hours before hatching, she discovered, the eggs began to emit faint and intermittent clicks in time with the breathing of the embryo. The clicking gradually became louder and more regular, drowning out the sound of breathing, until it suddenly stopped only minutes before the eggs hatched.
Psychologist Vince is not sure what causes the clicking, but she thinks it is associated with lung ventilation and serves as a form of communication be tween the eggs. As more mature embryos move toward the hatching stage, she says, their clicking stimulates faster development of younger embryos in adjacent eggs, so that all of the eggs hatch around the same time. To check her theory, she shortened the normal incubation period of a quail egg by placing it in a nest of other quail eggs that began incubation at least 24 hours earlier. Stimulated by the surrounding clicks, the newer quail egg hatched at the same time as the more mature ones.
The quail-egg experiments also demonstrate that the communication between eggs works only when they are in actual contact. When Psychologist Vince separated the eggs, placing them four inches apart, the embryos could not sense the clicks made by their siblings. As a result, they hatched independently—as much as two days apart.