Species distribution is influenced by biotic and abiotic factors, which may leave detectable signals in how species co-occur. Species co-occurrence describes the frequency at which two or more species are found together across various spatial locations, and if that frequency is positive, negative, or simply random by chance. Random co-occurrence refers to when two species are distributed independently of one another. When two species co-occur at more locations than expected if they were randomly distributed, it is referred to as positive co-occurrence. Conversely, when they co-occur at fewer locations than expected randomly, it is called negative co-occurrence. The positive or negative co-occurrence pattern may arise from the influence of species interactions (e.g., facilitation, competition etc.) and/or shared environmental responses of the species, (i.e., similarity or dissimilarity in habitat preference). The patterns of species co-occurrence can play significant role in shaping, for example, the avian community, where factors like competition over resources, facilitation of resources among species, similarities or differences in habitat utilization are evident.
The cavity-nesting bird communities, comprising excavators and non-excavators, offer a suitable model for studying species co-occurrence, as their relationship revolve around creation and availability of resources (e.g., nest sites), yet they have received less research attention. In this study, I investigated the patterns of interspecific co-occurrence in the cavity nesting birds, focusing on owls and woodpeckers in a managed forest in Southern Finland. I collected audio recordings from the Harviala forest from February to March 2025, and detected the presence- absence of the target species using sound analysis software Raven pro. The target species were the cavity-excavating woodpeckers: black woodpecker, grey-headed woodpecker, and great-spotted woodpecker, and the non-excavating owls: boreal owl, and pygmy owl. Using Hierarchical Modelling of Species Communities (HMSC) framework, my results showed that the owls and woodpeckers co-occurred more frequently than would be expected by chance. This co-occurrence was driven by both shared environmental responses and species interactions, with the former being the primary driver. Additionally, positive co-occurrence was observed between the boreal owl and the black woodpecker, as well as between the boreal owl and the grey-headed woodpecker, and between the Eurasian pygmy owl and the great-spotted woodpecker, as expected, due to their complementary nesting requirements. Understanding these patterns of species co-occurrence can increase the knowledge on the overall structure of the cavity-nesting community, which in turn, can inform the species and forest management in Finland. While further research is needed to deepen this understanding, the findings of my study still offer a valuable foundation for future management and conservation efforts.
The project resulted in the successful completion of my master’s thesis. It was carried out in collaboration with UPM, a leading Finnish forestry industry company, and the Finnish Osprey Foundation (Sääksisäätiö). This also opened doors for future collaboration opportunities with both of these organizations.