What characteristic of flight feathers influences the aerodynamics of a raptor?

The arrangement of secondary feathers plays a significant role in the aerodynamics of a raptor. Secondary feathers, located on the inner wing, are crucial for generating lift and providing stability during flight. Their arrangement allows for effective airflow over the wing's surface, which is essential for maneuverability and control in the air, particularly during hunting and navigating through complex environments.

This design feature enables raptors to achieve greater agility when soaring or diving, making them formidable predators. The strategic positioning of the secondary feathers allows a raptor to adjust its wing shape and surface area, optimizing lift and drag according to its flying needs.

In contrast, the other characteristics mentioned do not directly affect the aerodynamics of flight in a raptor. The size of the beak, for instance, primarily influences feeding and hunting capabilities rather than flight dynamics. The length of deck feathers might be relevant to feather function, but they are not the primary drivers of aerodynamic efficiency. Lastly, the scales on the tarsus relate to the bird's perching and hunting adaptations, rather than its aerial performance. Thus, the arrangement of secondary feathers is crucial for efficient flight and maneuverability, making it the correct answer.