Over on Twitter I found out why! Apparently the Vatican now has garbage cans with better lids, so the seagulls aren't gorging on tourists' discarded fries, or whatever, but have to earn a more meager living. No, really.
Biologist here! Large population, and not time for enough generations to get to the "everyone is distantly related to everyone" stage argues against it.
In favor: Yellow-Legged Gulls have been shown to be highly philopatric. (Although I don't know that "highly" extends to "on the same chimney.")
Comments
Sistine Seagull of 2013.
In favor: Yellow-Legged Gulls have been shown to be highly philopatric. (Although I don't know that "highly" extends to "on the same chimney.")