A groundbreaking study led by researchers at the University of the Sunshine Coast has revealed that sex reversal in wild birds, where individuals develop the physical or behavioural traits of the opposite sex, is far more common than previously believed. The discovery could have far-reaching implications for conservation efforts, especially for species already at risk.
Traditionally considered rare in avian species, sex reversal has now been observed in several populations of free-living birds across diverse habitats. Researchers say this phenomenon, influenced by environmental stressors such as temperature fluctuations and pollution, may play a larger role in bird biology and population dynamics than scientists had assumed.
The study entitled "Prevalence and implications of sex reversal in free-living birds" involved nearly 500 birds across five species, including magpies, kookaburras, pigeons, and lorikeets. Researchers discovered that up to 6% exhibited physical characteristics of one sex while possessing the genetic profile of the opposite sex.
"This indicates that sex determination in wild birds is more fluid than we thought - and can persist into adulthood," said UniSC Associate Professor Dominique Potvin, who co-authored the study published in Biology Letters on Wednesday.
The birds were examined after death following their admission to wildlife hospitals in southeast Queensland due to unrelated injuries or illnesses. Researchers assessed their reproductive organs and conducted DNA testing to determine their genetic sex.
"One of the key findings was that 92% of sex-reversed birds were genetically female but had male reproductive organs," Dr Potvin said.
"We also discovered a genetically male kookaburra who was reproductively active with large follicles and a distended oviduct, indicating recent egg production."
Although sex reversal is well-documented in fish, amphibians, and reptiles, it has been rarely observed in wild birds and mammals. This study offers an important baseline for understanding the occurrence of this phenomenon in Australia's bird populations.
"An optimally functioning reproductive system and operational sex ratio are crucial for population sustainability. While discordant birds are unlikely to be the sole cause of population decline, combined with other stressors, they may undermine conservation efforts. The rates found in our study of wild birds raise concerns about the impact on threatened species populations," the paper reads.
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