Patterns of co-occurrence in woodpeckers and nocturnal cavity-nesting owls within an Idaho forest

Abstract

ABSTRACT. Few studies have examined the patterns of co-occurrence between diurnal birds such as woodpeckers and nocturnal birds such as owls, which they may facilitate. Flammulated Owls (Psiloscops flammeolus) and Northern Saw-whet Owls (Aegolius acadicus) are nocturnal, secondary cavity-nesting birds that inhabit forests. For nesting and roosting, both species require natural cavities or, more commonly, those that woodpeckers create. Using day and nighttime broadcast surveys (n = 150 locations) in the Rocky Mountain biogeographic region of Idaho, USA, we surveyed for owls and woodpeckers to assess patterns of co-occurrence and evaluated the hypothesis that forest owls and woodpeckers co-occurred more frequently than expected by chance because of the facilitative nature of their biological interaction. We also examined co-occurrence patterns between owl species to understand their possible competitive interactions. Finally, to assess whether co-occurrence patterns arose because of species interactions or selection of similar habitat types, we used canonical correspondence analysis (CCA) to examine habitat associations within this cavity-nesting bird community. We found that Flammulated Owls co-occurred more with Hairy Woodpeckers (Picoides villosus), Northern Saw-whet Owls co-occurred with Northern Flickers (Colaptes auratus) and Red-naped Sapsuckers (Sphyrapicus nuchalis) and, when primary excavators were considered as a group, each species of owl was positively associated with the presence of woodpeckers. The owl species were distributed independently of one another suggesting a lack of competitive interactions. The CCA had relatively low explanatory power but suggested that habitat associations alone did not explain the patterns of positive co-occurrence we observed: Flammulated Owls and Hairy Woodpeckers associated with different habitats and Northern Saw-whet Owls, Northern Flickers, and Red-naped Sapsuckers appeared as habitat generalists. We interpret these patterns of co-occurrence and habitat use as evidence that woodpeckers facilitate presence of these species of owl and suggest management for forest owls could also include focus on the diurnal species with which they appear to associate. Profils de cooccurrence des pics et des strigidés nocturnes nichant dans des cavités dans une forêt de l'IdahoRÉSUMÉ. Peu d'études ont examiné la cooccurrence des oiseaux diurnes, comme les pics, et les oiseaux nocturnes, comme les strigidés. Les Petits-ducs nains (Psiloscops flammeolus) et les Petites Nyctales (Aegolius acadicus) sont des utilisateurs secondaires de cavités nocturnes nichant en forêt. Pour nicher et se reposer, ces deux espèces ont besoin de cavités naturelles ou, plus couramment, celles excavées par des pics. Au moyen de relevés diurnes et nocturnes accompagnés d'enregistrements sonores (n = 150 sites) réalisés dans la région biogéographique des Montagnes Rocheuses en Idaho, aux États-Unis, nous avons inventorié les strigidés et les pics afin d'évaluer leur tendance à cooccurrer et de valider l'hypo...