I live in a coastal town with a lot of seagulls. It’s that time of year when all the babies are leaving the rooftops and being killed by cats/ cars/ kids etc and complete chaos.
I always watch the rooftops of houses opposite as they always have a nest. I like to see how many they have, watch them grow and have been waiting to see if they leave this week. Two of them left over the last couple of days, leaving one on the roof. The mum and dad seagull were feeding the ones on the ground and the one on the roof still.
Then a couple of hours ago a seagull started attacking the baby on the roof. Grabbing it by the neck with it’s beak and dragging it to the edge of the roof. Then a black backed hull started swooping down and about ten other seagulls started swooping at the one attacking the baby. It looked like the black back was trying to get the baby and all the others were trying to stop it. Then another seagull started attacking the baby and they completely ripped it apart and pushed the bits of it off the roof 
. After that they all flew off, didn’t try to eat the baby or anything.
I don’t know if the seagulls attacking the baby were it’s parents or just some other ones but why did they do it? They didn’t eat it and if it was encroaching on another seagulls territory surely they’d have got rid of the eggs or done it when they were tiny.
Any ideas? I’ve never seen them hurt the young before. They always seem to work together normally. If a cat or buzzard is around they start calling and all nearby adults swoop at it until it’s gone. It seemed really weird behaviour and I’d love to know why they did it.