This video shows a Great Horned Owl attacking a female Great Blue Heron while she incubates eggs in the pre-dawn darkness on April 8 and 9, 2012. The footage was captured by a live-streaming cam that can film even in low light conditions above the Cornell Lab of Ornithology's Sapsucker Woods Pond in Ithaca, New York.
We do not no if this was just harassing or a territorial thing with the attack.
Its possible that the great horned owl wanted to take the nest for their own
A GHO as been know to take a GBH as prey but not usually.
The Great Horned owl usually dines on rodents and rabbits.