The brutal killing of 15 flamingos, some of which were beheaded as they slept, is being investigated by German police.
WARNING: Some readers may find the images below disturbing.
Nine of the birds, known for their long necks, long legs and bright pink plumage, were found dead in their enclosure at Frankfurt Zoo on Friday, and another six were found the following day.
On both occasions the killer, or killers, struck twice at night. Some of the birds were stabbed to death while others had their heads cut or torn off.
According to reports in the Frankfurter Allgemeine Zeitung police are now examining video footage from the zoo in an attempt to identify the person responsible.
The newspaper reports that very little blood was found at the scene, prompting investigators to suggest that the birds may have been stolen from the zoo and then killed before their bodies returned.