Cormorant and poo

for some bizarre reason this Cormorant sits on the edge of this breeding tern raft every day; at about 10 minute intervals the 4 - 6 Common Terns attack it from above leaving it well splattered with poo and no doubt a severe headache but it simply does not move and in fact doesn't even react; another Cormorant nearby was rather more nervous and dived under the water every time it was attacked even plunge diving from one of the tern's posts where it had been sat