Most woodpeckers excavate their own holes in trees in which to breed and roost. They are 'primary cavity users'. Many other birds that cannot create such cavities, but need them as nesting sites, depend upon woodpecker holes. Such species are called 'secondary cavity users'. Here is an example: a young Tengmalm's Owl (aka Boreal Owl) looks out from a Black Woodpecker hole. In some cases the distribution and even breeding success of secondary cavity users is linked to woodpeckers. Photo by Thomas Hochebner taken in Austria.