he first case of polygyny was documented in Great Horned Owls in northwest Montana, where 2 females incubated eggs, and raised 5 nestlings in the same nest, aided by a single male mate (photos by Paul Konrad).

Believe it or not, Great Horned Owls have already started nesting in many areas of the country. This wide-ranging species is notorious for being among the first birds to begin nesting throughout their range that covers much of the Western Hemisphere. In March 2023, researchers at the Owl Research Institute (ORI) observed 2 female Great Horned Owls apparently incubating eggs in the same nest in northwest Montana. Checking back on the owls revealed that one of the females abandoned the nest after a few weeks, leaving the other to finish incubating the eggs.

But during the spring of 2024, biologists observed 2 Great Horned Owls in incubation posture yet again, this time in another nest only about 100 feet from the 2023 nest. Subsequent observations showed there were 5 nestlings, a highly unlikely number for a single brood. The male was observed delivering prey to the nest and biologists heard vocalizations from all 3 of the adult owls. This information led the researchers to believe this was a case of polygyny, with 1 male paired with 2 females that apparently both laid eggs in the same nest. And the happy ending is that this apparent dual brood of 5 nestlings all fledged successfully from the nest.

Great Horned Owls are normally monogamous, with each male pairing with a single female, so this was a most unusual find. Another interesting aspect of this particular case of owl polygyny is that normally a male mates with and cares for 2 or more females, with each female laying a clutch of eggs in a separate nest. Although polygyny is highly infrequent among North American Owls, it has been documented in Barn Owls, Long-eared Owls, and Flammulated Owls, usually with the male providing for 2 different broods at separate nest sites.

While this appears to be the first documented case of successful polygyny in Great Horned Owls, it leads to some interesting questions, such as the genetic relatedness of the adult females and the nestlings, and the behavioral choices that led to the formation of a polygynous trio. Unfortunately, these questions are difficult to answer, but it is interesting that the polygynous bonds appear to have continued over at least 2 years, and it may continue into this nesting season – time will soon tell. This year, ORI field researchers plan to spend ample time observing the owls’ behavior, and possibly collecting DNA from these owls to better understand the relationships between the owls and their potential nestlings – if they nest in the area again!

This information was prepared from an article published in the ORI’s annual publication, The Roost. You can learn more about owls and the Owl Research Institute at Owl Research Institute