Why are bridges always surrounded by pigeons?
Pigeons are “rock doves”. They naturally nest on rock outcroppings and cliff faces. In a city the structural edifices of the buildings and bridges make for a near perfect replication of their natural nesting places.
What do pigeons eat? I figure bugs. In that case, Bridges offer nesting locations above water that attracts insects.
Bridges often contain many convenient ledges where birds can rest without worrying about being attacked by ground-based predators. Such structures tend to attract birds compared to other places.