Germany: Baby orangutan Rieke is bottle-fed at Berlin Zoo [Cute photos]

Like any new father, Ruben Gralki is learning just how much is involved in caring for a newborn. He gives baby Rieke her bottle every couple of hours, comforting her when she cries and changing her nappy. But Rieke is not his daughter – she's a baby Bornean orangutan and Gralki is a keeper at Berlin Zoo.

Rieke was born on 12 January but first-time mother Djasinga did not bond with her. Gralki stepped in as a substitute parent; he and another keeper take turns caring for her, feeding her every two to three hours.

Rieke is developing well and has put on 400g since she was born; she now weighs 2.29kg. When she is a bit older, Rieke will move to Monkey World Ape Rescue Centre in Dorset, south-west England, as a companion for an orphaned five-month-old Sumatran orangutan named Bulu Mata.

Until then, the public can see her being fed at Zoo Berlin every Saturday around 1pm - if she is awake.