Zoological textbooks generally state that right and left ovaries develop in the embryonic bird, but that only the left ovary persists in the majority of adults.
Proceedings of the Iowa Academy of Science
©1931 Iowa Academy of Science, Inc.
Fitzpatrick, F. L.
"Bilateral Ovaries in Raptorial Birds, with Notes on Kidney Structure,"
Proceedings of the Iowa Academy of Science, 38(1), 245-248.
Available at: https://scholarworks.uni.edu/pias/vol38/iss1/96