Use by maternity colonies of any kind, use for large hibernating colonies, use as a migratory stopover, and use for colonial reproductive behavior are relatively clear examples. Prudence dictates that any kind of use that is previously undocumented qualifies as well. Significance of use varies regionally and is generally best determined by the best judgment of bat biologists familiar with the region. Large numbers of underground mines were not a common feature of the environment in the western United States until a few decades before the dawn of the 20th century. By the same reasoning, we should not need wildlife preserves or national parks.
Many bat species are in decline as a direct or indirect result of human activity.
A significant part of this decline can be attributed to destruction of natural roost sites or human disturbance at roost sites. Species such as Townsend s big-eared bat are notorious for establishing maternity colonies in relatively exposed parts of caves and rock shelters. Equally notorious is their habit of abandoning a roost site, and their newborn young as well, because of a relatively slight disturbance. Recreational activities, although perhaps inadvertent, have had a strong negative impact on a number of bat species. Roost habitat destruction because of encroaching development, logging of old growth forests, and renewed mining have also taken a toll.