Why go to such extremes? It's all about advertising their existence to potential mates and is the most important contact signal during this courtship.  It begins now, in February, but doesn't usually peak until March or even April. Unusually, it is done by both male and female birds.

Once paired, they are usually monogamous for up to about three years and they each take their share of excavating their nest-hole in a tree, incubating the eggs and feeding the young.  The excavation of their hole is done more slowly than when they’re drumming so you won't hear the same noise.

It's not just their drumming that's impressive. Their tongues are long and sticky with a harpoon-like tip that they can use to impale their prey. It sounds gruesome but if you put yourself in woodpecker feet for a moment, it makes sense – it's perfect for poking and probing into crevices for insects and into conifer cones for seeds.  Their bills aren't used only for drumming and excavating; they can chisel into wood to expose wood-boring beetles and larvae (if you have a nest box in your garden, you'll know the importance of a metal ring around the hole as great spotted woodpeckers are partial to the odd nestling).