Having sampled a diverse range of sounds throughout the series, Aubrey now studies a selection of them in even greater detail to identify what elements convey meaning.

Attracting a mate is fundamental in the animal world. Aubrey identifies how sounds can act as an indicator of the quality of mate and looks at what it is about a complex song that proves a male will make a good partner.

Simple calls can also contain valuable information. The cries of nestlings indicate their degree of hunger to their parents, and cuckoo chicks, which parasitize the nests of reed warblers, use sound to fool the host parents into feeding them. Keeping one cuckoo happily fed is a task on a par with feeding four genuine reed warbler young.

Deciphering what sounds mean is no easy task, as Aubrey discovers when he travels to Amboseli National Park in Kenya. Joining Joyce Poole, Director of the Savannah Elephant Listening Project, he gains an insight into the meaning of different trumpeting calls.

In human language, sound also affects the meaning. Aubrey discovers that there’s more to language than just getting the words in the right order; and that when it comes to emotion, sound is the crucial ingredient.

Moving on from natural sounds, next week’s programme looks at how man-made noise has affected animal communication and whether we’re losing the natural song of the Earth.