Each autumn, a single jay — a blue and reddish bird about the size of a pigeon — buries around 4,600 acorns, according to a study by German naturalists. This figure comes from observing that 65 jays transported about 300,000 acorns in two months, averaging nearly 4,600 acorns per bird. These birds play a vital role in planting acorns, with at least 59% of young oak trees from natural regeneration coming from acorns they have buried. In France alone, jays are estimated to plant about 2 billion acorns each autumn, helping to sustain the country's oak forests. Jays have a special anatomical feature that allows them to carry acorns in a pouch under their beak. They can hold up to six acorns in their beak at a time, and the rest are stored in a pouch at the bottom of their throat. They then spit out the acorns one by one, placing them at a distance from where they were collected. The birds choose open areas, such as the base of thorny shrubs like blackthorn, wild cherry, and brambles, to bury the acorns. Each acorn is placed separately, spaced 50 centimeters to one meter apart and buried deeply with their beak. This method ensures that the acorns receive the light they need to germinate, which is often lacking under the dense canopy of mature oak trees. Jays can travel varying distances from the source of the acorns, ranging from 1 to 6 kilometers, with some individuals traveling tens of kilometers. Their spatial memory is quite good, but not perfect. They can retrieve most of their hidden acorns during the winter, but some remain buried and forgotten. These forgotten acorns then germinate in the following spring, contributing to the natural regeneration of forests. This imperfect memory turns the jay's behavior into a key mechanism for forest renewal. The relationship between jays and oaks is the result of thousands of years of coevolution. Oaks produce acorns rich in carbohydrates that make up nearly 50% of a jay’s annual diet and almost 90% of its winter food. In return, the jay acts as the main carrier for long-distance dispersal of oak seeds. Without the jay, acorns would fall mainly at the base of the parent tree, where they rarely germinate due to lack of light. Scientists refer to this mutualistic relationship as symbiosis, a term typically used for close biological partnerships. After the last Ice Age, oak trees were only found at the southernmost part of Europe. British paleobotanist Clement Reid calculated that natural seed dispersal would have taken hundreds of thousands of years to repopulate Europe. However, oak forests spread much faster — in just a few thousand years — a phenomenon known as Reid’s paradox. Researchers from INRA proposed that long-distance dispersal by animals like jays played a crucial role. These birds could carry acorns several kilometers, even up to 20 kilometers in some cases, creating isolated patches of oak trees that eventually spread across the continent. Today, the natural regeneration of French oak forests continues to rely on the repeated, though imperfect, actions of millions of jays each autumn. While only a fraction of the 2 billion acorns planted by French jays each year will grow into trees, their role in maintaining the forest is essential.