arcgis 10.1 - How to count the number of shapefiles that touch each polygon?

I am trying to assign a number value field to different habitat shapefile polygons that is the number of other habitat type shapefiles that overlap or share a boundary. For example, I have 5 different habitat type shapefiles. I want each habitat polygon within each habitat shapefile to have a value indicating the number of different habitats that it touches. So if a particular wetland polygon touches a forest polygon and a beach polygon, that wetland polygon would receive a score of 2. Thanks!