An evaluation of GIS-based habitat models for bighorn sheep winter range in Glacier National Park, Montana, USA (MS Thesis)

Dicus, Gordon

Logistic regression was used to construct bighorn sheep winter range habitat models for two Glacier National Park (GNP) study areas, one in the Many Glacier valley and one in the Two Medicine valley. During two winters, habitat use was described through systematic ground surveys supplemented with focal observations, lasting 1-3 days, of recognizable individual sheep. Lambing areas were identified through ground surveys conducted from May 1-June 15. Available habitat was evaluated using 14 habitat parameters, each measured at a 30-by-30 meter grid-cell resolution with GIS software. As a general measure of herd health, composite samples of bighorn sheep fecal pellets were analyzed for levels of fecal nitrogen (FN) and diaminopimelic acid (DAPA). FN content averaged 1.69% and DAPA content ranged from 0.29 to 0.40 mg/g, indicating relatively high quality winter forage. Candidate models constructed from Many Glacier habitat use data were validated at Two Medicine, and vice versa. Using habitat parameters from the model with the best validation test performance, two versions of a final GNP winter range model were constructed using data pooled from both study areas. The performance of the final GNP models was compared to that of a regional model (the Smith model GIS application). The GNP models correctly classified 75% of grid-cells with observed winter use at Many Glacier and 38% of grid-cells with observed winter use at Two Medicine. The Smith model GIS application correctly classified 10% and 11% of grid-cells with observed winter use at Many Glacier and Two Medicine, respectively. The GNP models also performed slightly better than the Smith model GIS application in predicting lambing areas. Habitat parameters in the final GNP models were distance to escape terrain, snow cover, solar radiation index, slope, and either land cover type (from a classified satellite image) or horizontal visibility and two satellite wavelength band reflectance values. The final models will be useful to GNP managers for identifying suitable bighorn sheep winter range potentially threatened by conifer encroachment, livestock trespass, exotic plants and/or illegal hunting pressure.

An evaluation of GIS-based habitat models for bighorn sheep winter range in Glacier National Park, Montana, USA (MS Thesis)

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