No breeding luck for our Caspian Terns again

CAspian terns 1
While the terns had a couple of goes at nesting this summer it now looks like they have left the Spit and given up for another year.
We are at a loss to know the reasons this time as the weather has been settled since before Xmas and the predator control has been working efficiently.
The black backed gulls have had another very successful breeding season and their numbers are definitely increasing.
Is there any connection? Maybe we need to find out more?
Enjoy the rest of this wonderful summer.