WHAT’S THE STORY?

NOLA, one of the world’s last four remaining northern white rhinos, has been put down at San Diego Zoo Safari Park in the US.

The 41-year-old female underwent surgery just 10 days ago to drain a hip abscess and, although the operation was deemed a success, her health deteriorated a week ago and she was put down.

Her death leaves just three of the subspecies still alive. They are all elderly and are kept under 24-hour armed guard at the Ol Pejeta Conservancy in Kenya.

Here, the animals have a 700-acre enclosure and a nutritious diet supplemented with fresh vegetables as veterinarians try to keep them healthy enough to increase the species’ longevity.

That’s where a big responsibility is heaped on the 1.2-ton frame of Sudan – the world’s last male northern white. But at the age of 42 (life expectancy is 50 years) his active mating days would appear to be over.

However, San Diego Zoo has introduced six southern white rhinos, hoping to use them as surrogates for their northern cousins.

They will harvest semen from Sudan and combine it with eggs from a female northern white, hoping to create an embryo that will be implanted in a southern white.

Researchers say if that works, a northern white rhino calf could be born within 15 years, but tests are still going on to determine if the two subspecies are genetically similar enough to use surrogates.

WHY ARE THEY SO SCARCE?

AS WITH many other species, blame the poachers whose activities in search of the beasts’ prized horns devastated their population, rendering them extinct in the wild in 2008.

The northern whites used to roam over parts of Uganda, Chad, Sudan, the Central African Republic, and the Democratic Republic of the Congo. As recently as 1960, there were more than 2,000 animals in the wild.

Although poaching is the main reason for the current low population, they also had to endure years of political instability and civil war in their home ranges, which did not help maintain their numbers.

By contrast there are around 20,000 southern whites remaining in the world.

HOW DO THE TWO TYPES DIFFER?

THERE is no colour difference between the two – both are grey – their name comes from the Afrikaans word “weit” meaning wide, and refers to the animal’s muzzle. Northern whites have a straight back while their cousins’ is more concave, with a prominent shoulder hump.

The shape of their palates also differs, and northern whites have smaller, lower-crowned teeth. Their skulls are different shapes.

Skin folds and the hair growth might also help distinguish between them, and the southern species have distinct grooves between their ribs. Their heads hang down low to the ground in both species and they look up only if alarmed.

They lead a sedentary, semi-social lifestyle and spend their days and nights feeding and resting. In hot, dry weather they rest in the hottest part of the day, much of the time wallowing in water to keep cool and shake off skin parasites.

White rhinoceroses are also territorial and the adult bulls solitary – only associating with females for the mating season.

As with all rhino species, their horns grow from the skin and consist of compressed strands of keratin (like our fingernails). The horns are not attached to the skull, but rest on bone stem. They grow continuously and, if broken off, they grow back.