In the fourth programme, the viewer is taken on a journey along the Andes, the spine of the continent. In the northern tropics, spectacled bears feed on bromeliads in the cloud forests and on the puya flower spikes in the alpine grasslands of the Páramo. At these altitudes hummingbirds find it difficult to hover, so those such as the Andean hillstar perch on flowers as they drink the nectar. The Andes are a young range in geological terms, and volcanic activity is still present.

• Fergal Keane