Think the RSPB may have a big problem where we have relative rare birds such as Bitterns as I feel sure they need to control corvids and gulls in these areas.I understand this year not very good for these birds breeding success and I think this is simply down to predation from these birds.The argument about corvids can only take what is plentiful falls flat when we have rare birds congregating in relative small reed beds.Having put so much effort into getting these Bitterns and others established Iwould hate to see them stand still or go backwards.
Sooty, I dont know what the breeding record is this year but if it is low that would be consistent with what seems (in my area) to be a bad year for gulls and waterbirds. The explanation has to be something to do with water levels. The River Thames near me was dry in January but is currently as high as it has ever been and is overflowing in places. I suspect the water level within reeds is critical to bittern success.
Visiting the Cotswold Water Park. Have a look at http://cotswoldwaterpark.wordpress.com/
I would have thought a site would have to have a large number of Bittern to attract a large number of corvids or gulls.There is certainly a lot more than control of them to getting Bitterns in the area otherwise some of the well keepered shooting estates would attract bitterns.
Birding is for everyone no matter how good or bad we are at it,enjoy it while you can