Scientists in Australia have discovered that sex reversal in wild birds—once thought to be rare—may be far more common than previously believed. Research from the University of the Sunshine Coast has found that around six per cent of birds in a study of five common Australian species, including kookaburras, magpies, and lorikeets, had the chromosomes of one sex but the reproductive organs of another.
The study, which DNA-tested nearly 500 birds, revealed that most cases involved genetically female birds developing male gonads. In a particularly striking example, researchers identified a genetically male kookaburra that was reproductively active as a female, with large follicles and a distended oviduct indicating recent egg production.
While sex reversal is well documented in reptiles and fish, it has been considered unusual in wild birds and mammals. The researchers suggest the phenomenon could be triggered by environmental factors such as hormone-disrupting pollutants or other ecological changes, though the exact cause remains unknown.
Co-author Dominique Potvin said the findings challenge long-held assumptions about avian biology. “This indicates that sex determination in wild birds is more fluid than we thought, and can persist into adulthood,” she explained. Potvin emphasized that understanding the mechanisms behind sex reversal is important not only for conservation efforts but also for improving the accuracy of bird population studies.
The study was published this week in the peer-reviewed journal Biology Letters.