Hole life: survival patterns and reuse of cavities made by the Lesser Spotted Woodpecker Dendrocopos minor

Abstract

Primary cavity-producers such as woodpeckers produce nest sites for several other cavity-nesting animals and, thus, are often considered to be keystone species. However, the persistence and occupancy rates of cavities are rarely known and as such the real importance of primary cavity-producers also remains unclear. Cavities of the Lesser Spotted Woodpecker Dendrocopos minor were monitored during their whole lifespan. The data include the annual availability and occupancy history of 106 cavities in a 170-km2 area in southern Finland during 1987–2018. The median survival time of a cavity was six years, but there were differences between the various forest types (range six to eight years). The median time for cavity fall was six years, and five years for cavity damage. Six bird species used the old cavities for breeding, with the Pied Flycatcher Ficedula hypoleuca the dominant species accounting for 53% of all occupancies. The cavity reuse rate in the Lesser Spotted Woodpecker was 3.6%. The mean occupancy by secondary cavity-nesting birds in old cavities was 32%, with a range of 29–36% across the various forest types. There was a significant negative correlation between annual occupancy rates and the age of the cavity. The first two years of a cavity were found to be the most important for total occupancy and 90% of occupancies took place before the median age of the cavities. The expected mean number of lifespan occupancies by secondary cavity-nesters for a single cavity was 1.97. The results indicate that new, fresh cavities are continuously needed for the secondary cavity-nesters that use Lesser Spotted Woodpecker cavities in their territories.