What historical necessity shaped the Dandie's loud bark in relation to underground hunting?

Answer

The bark needed to communicate the dog's location to the hunter above ground from deep within a tunnel.

The deep, resonant bark was successfully bred into the line so that the dog could communicate its location to the hunter above ground, regardless of how deep the tunnel ran while working underground.

What historical necessity shaped the Dandie's loud bark in relation to underground hunting?
Dogbarkbreed