Which of the following is a common biological threat to aviation?

Bird strikes represent a significant biological threat to aviation because they pose a direct hazard to aircraft, particularly during takeoff and landing phases when the aircraft is flying at lower altitudes and speeds. Birds can collide with engines, windshields, and other critical components of the aircraft, which may lead to serious damage or even catastrophic failure.

The frequency of bird strikes has been well documented and is of particular concern near airports, which are often located in environments that attract birds. Mitigation strategies are frequently employed, including wildlife management and habitat control around airfields, to reduce the risk these incidents pose to flight safety.

Other options do not relate directly to biological threats. Solar glare, for example, is an environmental factor that can affect visibility but does not stem from a biological source. Structural weaknesses refer to physical defects in an aircraft, and nerve agents are chemical threats that, while dangerous, do not pertain to biological organisms impacting aviation safety. Thus, bird strikes are clearly identified as a primary biological threat, making this choice the most appropriate.