When three Sumatran tiger cubs were born at Taronga Zoo on a cold August morning last year, keepers and veterinarians breathed a sigh of relief.
Sumatran Tigers are critically endangered, with as few as 400 estimated to be living in the wild. Only seven per cent of their original habitat remains, with palm oil plantations the major threat to the forests they live in. On top of that, tiger body parts continue to be used in traditional medicines, and tiger pelts fetch high prices on the black market. In fact, so great is the demand for tiger pelts that in 2009 a female tiger was poisoned, killed and skinned while in an exhibit at Rimbo Zoo in Indonesia (a suspect has since been arrested).
For these reasons, Taronga’s three cubs represent a staggering one per cent of the existing Sumatran Tiger population. Over the years the Zoo has made a significant contribution to Sumatran Tiger conservation, with the breeding program yielding 30 tigers since 1979. But the lead up to this birth wasn’t straightforward.
Father Satu was imported from Stuttgart Germany at the age of 18 months as part of the international zoo breeding program for Sumatran Tigers. Too young to breed, he spent around 18 months acclimatising at Western Plains Zoo before arriving at Taronga Zoo in January 2008.
When he did arrive he was kept in his own enclosure, as tigers are generally solitary animals. However, he had auditory and olfactory contact with Jumilah and was allowed into her enclosure when she was in oestrus.
Like domestic cats, tigers are induced ovulators, only ovulating with penetration during mating.
According to veterinarian Frances Hulst, tigers and domestic cats have much in common when it comes to being on heat – it’s just on a far bigger scale.
“There’s a lot of cheek rubbing on the sides of the enclosure and calling to the male,” she said.
The males are equally talkative.
“When he detects the female on heat he replies with a really impressive roar.”
Unfortunately, Satu didn’t follow up with any impressive moves in the boudoir.
“She would assume the breeding position and he would stand over her, grasp the scruff of her neck and make mating attempts but would never manage to penetrate ,” she said.
“He’d be a bit offset or try to mate her leg, he wasn’t quite getting it right and she was getting quite frustrated.”
Over several oestrus periods Satu did seem to be getting closer and closer to the mark, but veterinarians wanted to rule out any conditions which may have prevented him from performing his duty.
“The keepers had conditioned him to be hand injected with the anaesthetic which took a lot of the stress out of it,” Hulst said. “It’s really a major step forward when an animal does not have go through the process of being darted.”
“We did a full physical examination, paying particular attention to ensure that the external genitalia were all normal which they were. An ultrasound of the testes suggested that these were normal and we were able to collect urine from him which was full of normal looking sperm. Although you can’t really assess semen motility in urine we could tell he was making loads of sperm.”
Radiographic examination of the pelvis failed to reveal any abnormalities which might hinder the act of mating.
“We couldn’t find any medical reason why Satu could not breed given further opportunity to do so.”
The team did not have to wait long. Satu managed to work out what to do at his very next opportunity.
“It was pretty well the next oestrus cycle that he was able to successfully mate with Jumilah.”
The pregnancy was confirmed by measuring faecal progesterone since faecal samples can be collected without disturbing the animals.
“When tigers ovulate the faecal progesterone is elevated for the first 40-45 days, regardless of whether or not the animal is pregnant, since tigers undergo a pseudopregnancy. If the progesterone stays up after 40-45 days we assume the female is pregnant,” Hulst said.
Keepers prepared a cubbing den and, like clockwork, Jumilah went into labour at around 100 days. To minimise any disturbance (tigers are notorious for killing their young when disturbed), veterinarians observed the labour from afar on CCTV.
“With any big cat as a first time mum there is a chance through inexperience that she will not mother the cubs well. We also know with a first time birth there is a higher incidence of complications and often lower litter size.”
Indeed that is what appeared to be happening. After an extended period during which the labour did not progress, the veterinary team made preparations to intervene.
“We had just loaded up the van with all of the gear and she gave birth, unfortunately to a single, large stillborn cub.”
It was a disappointing outcome, but staff at the zoo had little time to dwell on it – Jumilah came back into oestrus quite soon after parturition, and Satu mated her successfully for the second time. Again an initial increase in faecal progesterone was not over-interpreted. The keepers felt that Jumilah was almost certainly pregnant. But faecal progesterone tests after day 45 revealed a drop in progesterone levels.
“Even so the keepers who monitor her carefully felt she was behaving as if she were pregnant,” Hulst said. “She didn’t appear to be coming back into oestrus.”
Repeat faecal progesterone levels revealed an increase.
“Cats can have fluctuating progesterone levels,” Hulst explained. “They went up again and remained high for the rest of the pregnancy.”
Again keepers prepared a quiet den for the expectant mother. And again, like clockwork, Jumilah went into labour around day 102 (the gestation period for tiger’s ranges from 98-105 days).
“This time it was almost a textbook parturition,” Hulst said. “She gave birth in the early hours of the morning of August 27 to three cubs – and she was very vigilant from the word go. She was responsive to them, she cleaned them, she positioned herself so that they could suckle. The first birth might have stood her in good stead for this one.”
Zoo staff left the cubs alone with Jumilah for the first ten days, after which the keepers with whom the new mother was most familiar began making brief visits when the tigress was stretching her legs in the exhibit.
“Everyone wore protective overalls and booties to minimise any foreign smells, but the idea was to condition the cubs to humans in advance of their first veterinary exam,” Hulst said.
Jumilah wasn’t fazed at all. And when it came time for their first veterinary exam, the cubs weren’t too fussed either.
“We were able to do the physical examination, vaccinations and microchipping without any stress or need for physical restraint,” she says. “We had a keeper distracting them with a soft toy to chew on, but our main aim was to avoid stressing them and avoid any alarm calls that the cubs might make that Jumilah would hear.”
The cubs are vaccinated with an inactivated F3 vaccine. While big cats are also susceptible to canine distemper virus however an appropriate inactivated vaccine is not currently available in Australia. Importantly the cubs were completely normal and healthy. This was a big relief.
“When Jumilah was born she was one of three cubs,” Hulst said. “All had bilateral vestibular dysfunction.”
The zoo undertook extensive testing to determine the cause of the condition, including examination by veterinary neurologist Georgina Child.
“We did a lot of investigative work, but ultimately did not uncover the cause. We could not rule out a familial cause however three out of three affected cubs born to two unaffected parents is not consistent with a single gene mode of inheritance.”
By the age of six or seven months the cubs were able to compensate for their condition, and by the time they were eight or nine months old they were completely normal, ambulating without any sign of vestibular disease.
“A problem like this is really challenging,” Hulst explained. “When you are looking at a total population of 400, each and every breeding animal is incredibly precious. When we consider that we could not prove the condition was hereditary we didn’t have the luxury of being able to exclude animals from the breeding program without causing more of a genetic bottleneck.”
“We were really pleased with this litter. Each cub was examined very carefully but we found no evidence of any abnormalities – they really are perfect.”
In addition to contributing to the international breeding program, Taronga Zoo supports the Sumatran Tiger by funding wildlife protection units in Sumatra. The aim is to decrease illegal logging, hunting and vigilante actions against wildlife. For further information about supporting this program, visit www.taronga.org.au