This Little Blue has moved into the ‘little rookery’ and can be found there all the time. It would make sense if he had been born there. They return to the same rookeries all the time.
However, he is still white, meaning less than 2 years old. And, the ‘little rookery’ has not been active for around 2 years.
Assumption, not born there.
Perhaps it as simple as there are plenty a small ‘fish things’ here to eat.