Which bat species is NOT among the commonly encountered colonial bats?

The reasoning for the choice of an endangered bat as the not commonly encountered colonial bat is based on the typical behavior and population status of bat species. Colonial bats are known for living in large groups and forming colonies, especially in roosts. The little brown bat, big brown bat, and Mexican free-tailed bat are all examples of species that exhibit these social behaviors, often roosting in substantial numbers, which makes them more commonly encountered in many regions.

In contrast, the term "endangered bat" refers to a classification that generally includes species that are at risk of extinction due to various factors, such as habitat loss, disease, or other environmental pressures. These endangered species often have reduced population sizes, and as a result, they do not tend to form large colonies like their more stable counterparts. This makes the endangered bat less commonly encountered in the wild.

Thus, the distinction that an endangered bat does not engage in the same colonial behaviors as examples of more common species directly supports the choice of this answer.