An integrated occupancy and space-usemodel to predict abundance of imperfectly detected, territorial vertebrates

1. It is often highly desirable to know not only where species are likely to occur (i.e. occupancy) but also how many individuals are supported by a given habitat (i.e. density). For many animals, occupancy and density may be determined by distinct ecological processes. 2. Here we develop a novel abundance model as the product of landscape-scale occupancy probability and habitat-scale density given occupancy. One can conceptualize our model as fully packing a landscape with home ranges or territories based on habitat quality, and then subtracting territories based on a probabilistic process that accounts for the fact that species rarely exhibit full occupancy across heterogeneous landscapes. The model is designed to predict abundance at fine spatial scales, using resolutions equal to or smaller than a single home range or territory. 3. We demonstrate this model on the Black-backed Woodpecker (Picoides arcticus), a species of management concern linked to post-fire forests. Occupancy is derived from a regional monitoring effort, while density given occupancy comes from a telemetry study of variation in territory size. A Bayesian framework is used to combine independent occupancy and home-range size models and predict abundance of Black-backed Woodpeckers at 4 fires that burned in 2012 or 2013. Predictions are evaluated with independently collected survey data, showing that the model is successful at predicting both absolute abundance at fires as well as relative abundance within and among fires. 4. The conceptual model presents a promising new framework for fine-scale modelling of density and abundance for other territorial yet elusive species. Telemetry and occupancy data are widely collected for many species, but rarely utilized in combination, and the ecological exploration of the factors that determine occurrence versus home-range size may provide useful biological insight. As applied to the Black-backed Woodpecker, the model provides a tool for resource managers to explore trade-offs in retaining burned forest habitat versus managing for other post-fire goals, such as salvage logging or reforestation efforts that require snag removal.