What is characteristic of activities in an alert area?

The characteristic of activities in an alert area is high volumes of flight training. Alert areas are designated airspace where both military and civilian pilots may operate, and they are identified to warn other pilots of potential hazards related to unusual, frequent, or concentrated flight activities, often conducted by training facilities. The presence of flight training activities indicates that there may be multiple aircraft operating in the same general vicinity, which increases the need for heightened situational awareness among pilots flying in or near these areas.

Other choices suggest exclusive or limiting activities that do not accurately reflect the essence of what an alert area encompasses. Prohibited activities imply that specific actions cannot take place in that airspace, which does not align with the operational nature of alert areas. Military traffic only suggests an exclusive use by military operations, while commercial shipping flights are not a defining characteristic of alert areas either. Therefore, recognizing high volumes of flight training as the characteristic activity highlights the need for caution and coordination in those environments.