In "The Final Warning," the phrase "Once a bird kid, always a bird kid" highlights the lasting bond and identity of the characters involved in the Maximum Ride series. The series revolves around a group of children with bird-like abilities who face extraordinary challenges, emphasizing themes of friendship, loyalty, and resilience.

The quote suggests that once someone is part of this unique group, their identity and experiences as a "bird kid" stay with them forever. It reflects the enduring nature of their bond and the impact their adventurous journey has on their lives, even beyond their immediate struggles.