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Up until recently, 18-year-old Bridget looked very much like your typical lioness. Then, last year, the long-time resident of Oklahoma City Zoo mystified local veterinarians and zoo staff by growing a mane far more typical of male lions.
As Gretchen Cole, an associate veterinarian at the zoo, explained in an interview with ABC News: "After a while, it became obvious to everybody that Bridget was developing something a little different.”
Zoo staff have taken blood samples to try and deduce the so-far-unexplained cause of her new “mini-mane”. These will be compared to samples taken from Bridget’s sister, Tia, who was born in the same litter but has not shown similar signs of hair growth.
One possible explanation could be found in a population of lions living in the Okavango Delta in Botswana, where at least five females – like Bridget – have developed manes. These maned females also display other more masculine traits, including roaring, scent-marking, and mounting females.
Experts believe excessive testosterone levels are behind the typically more masculine appearance and behavior. While there are certainly some benefits to these changes (for example, they tend to be larger, stronger, and, therefore, excellent hunters of large prey), it comes at an evolutionary price. The surge in testosterone has been linked to infertility.
The fact that this phenomenon seems to be relatively common in this one area has led zoologists to believe there is a genetic factor involved. But this may be less likely in Bridget’s case, who, at 18, is geriatric by lion standards. The average life expectancy for a wild African lion (Panthera leo) is 15 years but those living in captivity can live to 30, according to the Zoological Society of London. Meanwhile, male lions first experience mane growth around the age of one, when the process is triggered by a flood of testosterone.
Cole believes there is a hormonal component to Bridget’s condition and the blood tests should help confirm or dismiss this theory. One possible cause could be a benign tumor on the adrenal or pituitary glands. Both areas are involved in hormonal regulation. Alternatively, there could be a problem in the ovaries, which is producing a surplus of testosterone, as was the case for Emma, the 13-year-old lioness living in the National Zoo, South Africa, a few years ago.
Whatever the cause, it doesn't seem to be doing Bridget any harm. "Zoo veterinary staff will continue to monitor her closely, but this condition is not likely to affect Bridget’s quality of life," Oklahoma City Zoo and Botanical Garden said in a statement on Facebook. "They report that, other than the extra hair, they see no change in her health status."
