Mixed-up Birds  

Sex determination in birds might not be as straightforward as scientists thought.  

A new study of nearly 500 birds from five Australian species found that up to 6 percent had the physical characteristics of one sex but the genetic makeup of the other. 

The species in analysis were Australian magpies, laughing kookaburras, crested pigeons, rainbow lorikeets, and scaly-breasted lorikeets, according to Smithsonian Magazine. The birds were analyzed after they all died at wildlife hospitals. 

Researchers tested their DNA and cross-checked it with their reproductive organs to determine the genetic sex of each bird. In the study, sex-reversed birds were categorized as genetic males but with female physical features, genetic females with male physical features, or birds showing a mix of both. 

The findings reported that 24 of the birds were sex-reversed, with the kookaburras showing the highest rate of sex reversal at 6.9 percent and the magpies the lowest at 4 percent. About 92 percent of the sex-reversed birds were genetically female with male reproductive organs. 

“I was thinking, is this right?” study author Dominique Potvin told the Guardian. “So we rechecked, and rechecked, and rechecked. And then we were thinking, ‘Oh my God.’” 

The team also found a genetically male kookaburra with female genitalia that indicated recent egg production, Potvin explained in a statement. 

Sex reversal is known in fish, amphibians, and reptiles but is rarely documented in wild birds and mammals. The reasons for the phenomenon in birds remain unclear. 

“Understanding how and why sex reversal occurs is vital for conservation and for improving the accuracy of bird research,” Potvin said in the statement. 

Sex-reversed individuals could influence reproductive success in wild populations, prompting concerns about potential effects on threatened species. “This can lead to skewed sex ratios, reduced population sizes, altered mate preferences, and even population decline,” study author Clancy Hall said in the statement. 

Researchers hypothesized that the reversal could be influenced by environmental factors, like endocrine-disrupting chemicals and high levels of stress hormones. For example, the genetically male kookaburra, which was also reproductively active, was found in an agricultural zone near an urban area, where those chemicals are often found. 

The presence of sexually ambiguous birds also complicates how researchers determine the sex of birds.  

“Bird researchers often take small DNA samples from blood or feathers and make decisions based on the results showing male or female, but this actually could be wrong up to 6 percent of the time,” said Hall.