This subject has come up elsewhere recently - most people would agree with you. Anyone caught doing such a thing should be escorted from the premises!
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I'll personally throw anyone I see doing that into the River Lea.
Of course we all agree on the subject. This seems to be based on hearsay and wonder why it was not officially reported. I have spent many days in the Kingfisher hide over the last few years and not seen such recorded calling - if I did, I would tell them to stop and report it to the Centre, by phone if necessary.
Most devices (such as iPhones and Smartphones) that are sold in the EU have a theoretical maximum volume of 100Db. I wonder if that would be loud enough to be heard by the Kingfishers?