Arthur W. Allen 1987 A review and synthesis of existing information were used to develop a Habitat Suitability Index (HSI) model for the gray squirrel (Sciurus carolinensis). The model consolidates habitat use information into a framework appropriate for field application, and is scaled to produce an index between 0.0 (unsuitable habitat) and 1.0 (optimum habitat). HSI models are designed to be used with Habitat Evaluation Procedures previously developed by U.S. Fish and Wildlife Service. application/pdf en U.S. Fish and Wildlife Service Habitat Suitability Index Models: Gray squirrel reports