Great Horned Owl vocalization question

We recorded these two birds in our backyard in San Ramon tonight about 6:30 pm (total darkness with moon rising).
One bird is obviously an adult Great Horned Owl.
But what's the other one shrieking?
Based on the fact that both birds were vocalizing in the dark and relatively near each other, we presume that it's another GHOW.
But we've never heard this vocalization, nor do we find much in the literature about it.
Any thoughts or opinions welcome.

Steve and Carol
San Ramon

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