Retriever got some great shots of baby Great Horned Owls yesterday, in a nest about 25' above the ground in New England. Great Horned Owls nest early, laying their eggs while the snow flies. These babies are probably raised on delicious rats and crows, and the occasional squirrel, skunk, and house cat for variety.
The nest itself is probably a renovated crow or squirrel nest, since Great Horned Owls do not build nests themselves, as far as I know. Most likely squirrel, with all of the leaves in it.