What specific feature is noted about the wryneck's requirement for nest cavity floors?

They do not line the bottom of the nest cavity; the bare wood serves as the base.

When selecting or preparing a nesting cavity, whether excavated or pre-existing, the wryneck exhibits a notable absence of lining material. Unlike some other cavity-nesting birds that might accumulate soft materials for insulation or cushioning, the female wryneck lays her clutch of white, glossy eggs directly onto the bare wood substrate of the cavity floor. This preference is an important distinction for conservation monitoring, especially when setting up nest boxes for woodpeckers, as adding wood shavings or other materials to a box intended for a wryneck would be contrary to its natural nesting requirements.