Social monogamy has been observed in less than 10% of mammal species – and birds have been shown to be less faithful than previously believed

In 2011, a shock celebrity break-up garnered headlines around the world – not the separation of Ashton Kutcher and Demi Moore, nor Jennifer Lopez and Marc Anthony, but the sudden, inexplicable rupture between Bibi and Poldi, two 115-year-old Galápagos tortoises at Happ reptile zoo in Austria.

After nearly a century as a couple, the female, Bibi, had had enough: one day, she bit a chunk off Poldi’s shell, drawing blood, and continued to attack him until zoo staff moved him to a separate enclosure.