Not even the strictest marriage guidance counsellor could have accused them of lacking commitment to their relationship: Bibi and Poldi had been living in harmony together under the same roof and in different cities for a staggering 115 years.

But crestfallen keepers at Klagenfurt Zoo in southern Austria were forced to admit yesterday that after more than a century, Bibi and Poldi – the names of the country's oldest living captive giant tortoise pair – had had a furious row, split up and were flatly refusing to share a cage.

"We get the feeling they can't stand the sight of each other anymore," is how Zoo director Helga Happ explained the motive behind Austria's deepening giant tortoise trauma. "For no reason anyone can discover, they have fallen out."

Zoo staff were stung into the bitter realisation that the pair's relationship had "turned turtle" when a keeper approached their cage last month and was given a wholly unexpected display of unfettered female giant tortoise fury.

Bibi attacked Poldi and bit off a chunk of his shell. She carried out several further attacks, obliging keepers to move Poldi to a separate cage for his safety.

The two giant tortoises were each born in 1897. "They are both 115 years old," Mrs Happ said. "They have been together since they were young and grew up together, eventually becoming a pair," she added. The two animals have been at Klagenfurt Zoo for 36 years. Before that they were kept at Basel Zoo in Switzerland.

Staff at Klagenfurt Zoo said that nothing had changed in the pair's routine. They said that by attacking Poldi, Bibi had clearly demonstrated that she wanted to have their enclosure for herself and continue life as a single giant tortoise.

Keepers said yesterday that they were trying a series of ruses in an attempt to bring the two giant tortoises back together. "We have keepers talking to them and trying to engage the two in interacting," Mrs Happ said. So far, nothing has worked.

Exposed: The sexual habits of tortoises

* Giant tortoises do not reach sexual maturity until 20-25 years in captivity, or up to 40 years in the wild. They are not monogamous. As a result of dwindling numbers, for some species the greatest barrier to reproducing can be finding each other.

* In the wild males will establish which is dominant by stretching their necks as high as possible with their mouths open. Frustrated males have been observed in the wild trying to mate with other males, or even rocks.

* After the male performs a mating dance that involves rhythmic head bobbing, foreplay can become aggressive. The male will often ram the female with his shell and immobilise her by nipping her legs to make her withdraw them into her shell.

* Mounting a female can prove difficult for a male as he has to balance himself on top of her shell. If he falls off there is a risk of him toppling on to his back, which can be life-threatening.

* Mating may last several hours and the males may roar hoarsely, one of the few times tortoises make any kind of vocalisation. After mating, the female digs a deep cylindrical hole with her hind legs, into which she lays up to 16 billiard ball-sized eggs.