Simply evidence that they are living in a particular habitat. This could be currently used burrows, nest sites, or simply observations of animals foraging, resting, or engaging in other natural behaviors which are indicative of use of that habitat or location.
First you have to define (or reference published descriptions) of the species habitats classified of interest for your particular study or area. Second you need to identify what you consider adequate evidence that the animal species in question is actually living (occupying) the site. Usually evidence of nesting, burrowing, foraging, breeding are typically the kinds of behaviors which are readily observed or leave physical evidence. Finally, you may wish to describe relative importance of ’habitat types’ based upon the relative amounts and/or types of evidence recorded.