Which factor contributes to increased energy needs for captive raptors?

Increased energy needs for captive raptors are significantly influenced by the factor of being flown hard. Raptors are highly active birds of prey that require substantial physical exertion to maintain their strength, endurance, and overall health. When they are flown hard, which typically involves rigorous training, exercise, or hunting activities, their metabolic rate increases to fuel this heightened level of activity.

This increased energy expenditure necessitates a corresponding increase in their food intake to ensure they are receiving adequate nutrients to sustain their energy levels and recover from the physical demands placed upon them. Proper nutrition is crucial for maintaining their physical condition and enabling them to perform optimally during flights and exercises.

Other factors like stress from human interaction could affect a raptor’s overall health and behavior, but it does not directly translate to increased energy needs like strenuous exercise does. Similarly, while excessive heat can influence a raptor's activity level or behavior, it can cause lethargy rather than a higher energy requirement, and being in a dark environment doesn't require an increase in caloric intake. Therefore, the correct choice is linked to the specific physical demands placed on the bird during flight activities.