Bruthöhlen

Bruthöhlen, literally “breeding hollows” in German, is a term used in ecology and ornithology to describe natural or artificial cavities that serve as nesting sites for breeding animals. The concept encompasses cavities in trees, rocks, cliffs, and other substrates, as well as human-made structures such as nest boxes, drilled timber holes, and ceramic or metal cavities. Bruthöhlen are critical resources for a variety of species whose reproductive success depends on secure concealment from predators and stable microclimates.

Structural factors that determine suitability include entrance diameter, depth, height above ground, humidity, and temperature. The size and location of a hole influence which species can use it. Primary cavity nesters, such as many woodpeckers, excavate their own cavities, whereas secondary cavity nesters rely on existing holes created by others or by natural processes. Birds such as tits, owls, and some swallows frequently use these cavities, while bats and other small mammals may roost in crevices or hollows that function as maternity sites.

Ecology and conservation: Bruthöhlen are a limiting resource in many ecosystems. Loss of old trees, snags, and natural cavities reduces available nesting sites and can affect population trends. Conservation measures include maintaining habitat features that promote cavity formation (such as standing dead trees), protecting existing cavities, and installing appropriately designed artificial nest boxes to supplement natural availability. Management plans often tailor cavity provision to the needs of target species, considering hole size, competition, and predation risks.

See also: nest box, cavity nesting, woodpecker, bat roost.