DV, please take it from one who does know, they were Gulls which were congregating in a farmers field in the undershoot. The farmer had taken to using this area as a tip.
ps Chugalug2, the crew member who ran quite a distance from the aircraft with a broken femur was the Flight Engineer (his name slips my memory); he was found to be in shock, unsurprising considering what had happened to the other 2 Flight Deck crew.