How do fused tail vertebrae help a bird?

Fused tail vertebrae, known as the pygostyle, provide structural support for a bird's tail feathers and muscles, enhancing stability and maneuverability during flight. This fusion allows for a stronger and more streamlined tail, which aids in steering and braking. Additionally, the pygostyle helps in balancing the bird while perched and assists in various social displays. Overall, it contributes significantly to a bird's overall aerodynamics and agility.