The secret call of the wild: how animals teach each other to survive

Cultural knowledge, passed from animal to animal, is key to how species adapt to change in the world around them

Sam Williams' Macaw Recovery Network in Costa Rica rewilds captivity-hatched fledgling scarlet and great green macaws. But introducing young birds into a complex forest world - bereft of the cultural education normally provided by parents - is slow and risky.

For 30 years or so scientists have referred to the diversity of life on Earth as "biological diversity", or just "biodiversity". They usually define biodiversity as operating at three levels: the diversity of genes within any particular species; the diversity of species in a given place; and the diversity of habitat types such as forests, coral reefs, and so on. But does that cover it? Not really. A fourth level has been almost entirely overlooked: cultural diversity.