The best way to find poachers is by passive detection. Areas known to be popular with poachers can often be detected from the air by spotting concentrations of wildlife in areas that are not normally frequented. Rangers on foot may also suspect poachers if they witness suspicious activity, such as groups or individuals hunting outside the authorized season, or poaching in protected areas where it is prohibited. If there is enough evidence available, anti-poaching rangers may also make use of tracking dogs to follow a particular animal or person.