大象传媒

David Attenborough visits a prairie dog town by Devil's Tower in Wyoming. On the open grasslands of the American west, it's very exposed and small animals are vulnerable. So prairie dogs dig for protection and have an alarm system to alert each other to dangers. Below ground is a warm safe refuge. They are so successful they can proliferate in huge numbers and form great settlements with hundreds of tunnels and burrows? But digging is hard work, so why do they make so many tunnels? David Attenborough uses a candle to demonstrate that connecting the holes isn't only about lots of escape routes, it's also about ventilation. Differently shaped entrances are designed to pull fresh air through the tunnel. One entrance is low to the surface of the prairie, the other has a sort of chimney. The wind blowing over the prairie moves faster a foot above the ground so it sucks stale air out of the higher entrance. In effect, the burrow is air conditioned.