In order to survive, all forms of life that we see around us have adopted a bizarre range of life strategies. I have recently been watching European common cranes spending the winter in southern France. Last March, we heard early arriving cuckoos in France calling in March!
This year, we watched several trios of cranes consisting of a male, female and one offspring feeding and preening together, getting ready for their long spring migration flight to northeast Europe. The youngsters were following their parents wherever they went looking for food, consisting of mainly unharvested maize seed heads and insects etc. When the time comes in February/March, the young birds follow their parents on migration towards Scandinavia and the Baltic states for the next breeding season. We watched a chevron of 35 cranes doing just that. During migration young birds separate from their parents and become independent, or get chased off when the parents start nesting. However, young cranes do not breed for several years, but still migrate to find sufficient food and, eventually, a mate and a nesting site.
In contrast to cranes, a cuckoo never knows it’s true parents, but still knows how to migrate and where and when to move. Not only that, but they also know to specialise in eating hairy caterpillars, a food that their surrogate parents never fed to them! All cuckoos are raised by surrogate parents whose nest has been used by a female cuckoo to lay a solitary egg in. Female cuckoos can lay from 12 to 22 eggs per year, each in a separate nest built by another bird species such as a reed warbler or meadow pipit for example. By the time the egg hatches, the adult cuckoos have left the area and will probably be migrating back to Africa. So, the nestling cuckoo will probably never even hear its parents calls, but will still know how to make those calls next spring. It is only the male that makes the familiar cuckoo call. Also, later in the year, the baby cuckoo will know exactly how to get to Africa for the winter without being taught how to get there by any other bird.
Herein lies the mystery of how much in animal behaviour is nurture and how much is inherited natural behaviour that can be described as some kind of genetic memory? Also, do we have any of this?