A southern white rhinoceros calf was born at the San Diego Zoo Safari Park to a mother who had gone nearly a decade without being able to get pregnant, zoo officials announced Thursday.
The female calf was born April 30 to mother Kiazi and father Maoto. Zoo officials said Kiazi has mated regularly since her arrival at the park in 2008, but had never before conceived. At 16 years old, she is past the average age that most southern white rhinos have their first calf.
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Zoo researchers say the answer could be involve a diet change.
Christopher Tubbs, a senior scientist in reproductive sciences at the San Diego Zoo Institute for Conservation Research, has been working with colleagues for nine years to discover why zoo-bred southern white rhinos don't bear offspring as often as their wild relatives. The problem is not found in other species of rhinos living in zoos.
They discovered that the animals may be sensitive to compounds called phytoestrogens — found in soy and alfalfa — that are a component of their diets in zoos. During their 16-month gestation, female calves could be exposed to the compounds through their mother's diet, resulting in infertility issues later in their life, according to the researchers.
"The birth of Kiazi's calf gives us a great deal of hope that by feeding low phytoestrogens at our institution and others, we can once again have a healthy, self-sustaining captive southern white rhinoceros population," Tubbs said.
"With the high level of poaching currently happening in Africa, having a healthy (off-site) population of rhinos is as important as ever," Tubbs said. "This calf is an example of how we are using cutting-edge laboratory science to lead the fight against extinction."
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San Diego Zoo Global changed the diet for southern white rhinos three years ago, to include less phytoestrogens and more nutrients to support reproduction. Since then, there have been three pregnancies in females that had not successfully reproduced before, which resulted in the birth of two healthy calves, according to the zoo.
Kiazi's calf is the 96th southern white rhino calf born at the San Diego Zoo Safari Park since 1972. Zoo officials often wait a few weeks before announcing animal births.
Estimated to weigh around 125 pounds at birth, the calf will nurse from her mother for up to 14 months — and she is expected to gain about 100 pounds a month in her first year. When full grown, at around 3 years of age, she could weigh 4,000 to 5,000 pounds.
The rhino calf and her mother can best be seen roaming their habitat from the Africa Tram Safari or a caravan safari.
Southern white rhinos are listed as "nearly threatened" on the International Union for Conservation of Nature Red List of Threatened Species, while three other types of rhinos are critically endangered.
