This documentary series continues tonight revealing the secret life of the animals of Chester Zoo, one of Britain's most popular zoos. They use new micro-rig technology to capture the behaviour of the animals and their close relationships with their keeper. It's very cute altogether. Tonight, a female Sumatran tiger Kirana faces losing her two sons, who are fully grown and being moved to other zoos to start families of their own. Indonesian dwarf buffalo Oana, one of Chester's most sensitive animals, gives birth - only for the new mum's anxiety to threaten her calf's health. Capuchin monkey Maud's eldest son Rocky is causing problems, refusing to listen to his mother's life lessons, and capybara Lochley has to rely on her mum Lilly to look after her newborn babies when she falls ill.