Northern Goshawk Models

The Northern Goshawk Nesting Suitability model displayed here was developed to support a resource management plan. The model coverage was created using ArcGrid™ with forest cover data. The variables used to develop the model were height class, canopy closure, tree species, and edges.

The structural maturity of a stand, and trees within a stand, form the fundamental basis for nesting suitability. After the fundamental requirement of a mature forest stage, canopy is probably the most important structural variable relating to nest suitability. Suitability depends on the form and structure of the trees and stands and can therefore vary with site and age. Hemlock seem to be preferred because they often form even-aged stands with closed canopies and open understories, and the branching pattern creates good nest platforms. Data from a sample of nest areas indicates that goshawks tend to avoid locating nests near forest edges, and this was also taken into account.

In the Foraging Area model, the variables used to develop the model were height class, age class, canopy closure, elevation, slope, and shoreline. Both age and height classes have a strong correlation and, therefore, have a significant influence on the model. Moderate to high canopy closures tend to correlate to open understories, which goshawks use as flyways while hunting. Stands with lower or higher canopy closures received reduced ratings. Data indicates that goshawks forage less at higher elevations, and this factor was also rated accordingly. Lower gradient slopes are given a higher rating, as these are typically richer sites that produce larger trees and are associated with higher prey densities. Similar to elevation, this factor is weighted lightly in the model. Goshawks appear to use the forest edge as cover as they hunt the rich diversity of prey (northwestern crow, alcids, gulls, ducks) that is available along the shoreline. These areas received a higher habitat rating.

On the map, the nesting suitability model coverage is displayed draped over a shaded relief derived from digital elevation model data that includes hydrology. The intent is to enable the viewer to develop an intuitive and map-based understanding of the distribution of the suitability model and to explore its spatial relationship to the topography and hydrology.