Recent paper assesses habitat suitability models for northern spotted owls

The northern spotted owl is a species of significant conservation concern, and management of the species has had important implications for forest management in the Pacific Northwest. A recent paper evaluated the potential and limitations of a critical habitat analysis by the U.S. Fish and Wildlife Service that included a range-wide analysis of owl nest site data using statistical models. 

The paper, which was authored by Craig Loehle and Larry Irwin of NCASI, and Brian F. J. Manly and Andrew Merrill of Western Ecosystems Technology, Inc., appears in Forest Ecology and Management. Based on their evaluation, the authors identify several aspects of the Service’s critical habitat analysis methodology that warrant consideration.

The abstract for the paper follows.

“Recently the US Fish and Wildlife Service, as part of a critical habitat analysis for the northern spotted owl (Strix occidentalis caurina), developed habitat suitability models based on thousands of owl nest sites distributed across 11 regions using the MaxEnt tool. Because these models formed the basis for critical habitat designations on millions of hectares of land, we undertook an independent evaluation of the FWS effort. We evaluated the accuracy of vegetation data used as input to develop the models, conducted out of sample analyses, correlated model output with owl reproductive success in two study areas, and developed alternate models using two different statistical methods. Vegetation data appeared accurate for only a few variables, and accuracy varied among model regions. Out of sample testing gave a high rate of classification errors and owl productivity was not correlated with MaxEnt model output in two study areas. Alternate statistical methods produced reasonable models with fewer variables. Critically, neither the models compared across regions nor the regions analyzed with different tools led to comparable use of variables. Thus biological interpretation of owl habitat selection models seemed ambiguous. In addition, for MaxEnt and one of the other tools, a highly significant trend by regression was found showing decreasing model accuracy as number of training nest sites increased. Together, these two results suggest that the generated models may be spurious to some unknown degree, perhaps because the underlying vegetation data, also derived from a model, are not sufficiently accurate to support the analysis and/or because the owls themselves affect habitat suitability by consuming their prey base. We suggest that the USFWS exercise caution in using MaxEnt models as a basis for regulatory purposes such as consultation, estimating likelihood of occupancy by owls, or evaluation of site-specific recovery actions.”



Loehle, C., L. Irwin, B.F.J. Manly, and A. Merrill. 2015. Range-wide analysis of northern spotted owl nesting habitat relations. Forest Ecology and Management 342:8–20.