A chicken in Cambridgeshire, England, shocked its owners when it seemed on the verge of a natural sex change.
Owner Jeanette Howard and her husband began noticing the changes after the hen, Gertie, began to moult, the BBC reports.
"She grew back lots more feathers -- she was quite straggly before -- and I also realized that she had filled out quite a lot. Gertie looked very healthy," Howard told the BBC.
Besides the fuller feathers, Gertie began to develop wattles, and her comb became larger and more distinctive, like that of a rooster.
Soon, Gertie was strutting around the coop and crowing.
"She wasn't very good at first, but she's progressed nicely and now she really goes for it," Howard said.
Veterinary surgeon Marion Ford told the BBC that changes in hens' gender-related traits are not uncommon and could be caused by fungi in stored animal feed, which act like synthetic hormones.
"An increase in testosterone will result in a hen growing an extended comb, exaggerated wattles and cockerel-like behavior, including strutting and crowing," Ford told the BBC.
Now, Gertie enjoys "frog-marching" around the garden and has stopped laying eggs.
"I'm not really sure whether Gertie has actually changed sex," Howard tells the BBC, "but to all intents and purposes, she's now a cockerel."