Leon Resnick, an employee of Riva Yamaha, was testing the water jet-propelled craft on Thursday on a lake near Fort Lauderdale, investigators said on Monday.
A co-worker who was watching turned to pick up a radar gun to check Resnick's speed, and when he turned back Resnick was no longer aboard the craft.
Resnick, 31, of Hollywood, drowned after suffering a blow to his head, the Broward County medical examiner's office said.
"Our theory is that the bird was airborne and clocked him in the head," said David Bamdas, an owner of the dealership.
The bird's carcass was found nearby and there were feathers on the water bike's handlebars, said Broward County sheriff's spokesperson Hugh Graf. - Sapa/AP