From CADORS – An Air Canada Boeing 777-333ER (C-FIUV / ACA858) from Toronto, ON (CYYZ) to London, England (EGLL) departed Runway 06L at 0353Z and was climbing through 2000 feet, when it reported striking an object. At 0355Z, the aircraft requested to dump fuel and to return to CYYZ. Then at 0425Z, the aircraft transmitted PAN PAN PAN. Emergency equipment was called out and ACA858 landed safely at 0446Z. An inspection of the aircraft revealed a dent over the left cockpit window and blood spatter on the fuselage. No identifiable bird carcass was found.