The marital aid is simple. It's a lot easier to carve wood than it is stone. This was the "home version" of taking care of business while the men were out on long hunting parties. If they rotted out, it was easy to replace and the male mates even used them between bouts as they got older and hit their 20s and thirties. I'll refer you to Charles Panati's book Sexy Origins of Intimate Things.
The bird has a different story. Evolving from the smaller, ground dwelling Dinosaurs, they had started growing feathers to help keep them warm. Studies in my own lifetime have determined that not all of the thunder lizards were cold blooded, as I was taught in second grade. As the feathers were good insulators, they also became more ornamental and multifunctional. As these mutations don't just happen overnight, it took time for each generation to evolve to nest fit it's environment.
The smaller birds went after bugs and grubs in land, while others went after aquatic life such as fish and algae. Feathers evolved into wings that, initially, was only good for gliding.
From these proto birds, evolved the woodpecker to catch its prey where it lived. Mutations that did not work died out through natural selection. Those that did survive stayed in. The extra long beak, the shock absorbing skull, evolved into the current anatomy so that it could catch it's favorite foods that were under the tree bark, eating the trees.
One trait the woodpecker shares is the plumage difference between genders. Most birds, including woodpeckers, the female is considered somewhat dowdy in appearance to better hide and camouflage the nest. The ladies love the brightly plumed males as they are looked upon as not only being braver, but that their brighter feathers will draw preditors away from their nests. You can find more on this by googling the evolution of the woodpecker. But if you think this was a long reply, you won't want to pursue it.
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