A wild fox broke into a zoo and savagely mauled 25 flamingos to death, leaving staff devastated.
The massacre was discovered during routine checks on Monday morning (May 2) at Smithsonian's National Zoo in Washington DC.
Staff arrived to find the slaughter and spotted a fox which escaped shortly after, the zoo said.
It is thought the fox got through a baseball-sized hole in the heavy mesh fencing surrounding the enclosure before going on the spree.
The zoo said a Northern pintail duck was also killed, and three other flamingos were hurt and are being treated.
Brandie Smith, the zoo's director, said: "This is a heartbreaking loss for us and everyone who cares about our animals.
“The barrier we used passed inspection and is used by other accredited zoos across the country.
"Our focus now is on the well-being of the remaining flock and fortifying our habitats.”
The birds killed are American flamingos, best known for their reddish-pink colour.
The flock, which originally had 74 flamingos, has now been moved to an indoor barn and the ducks are in a covered, secure outdoor space, the zoo said.
It comes as more and more stories are coming to light about animal welfare in zoos.
One park in Armenia was recently named the "world's saddest zoo" as a blind bear has been locked in a cage for 30 years, and miserable monkeys are shrouded in darkness.
Animal welfare groups are attempting to get the centre - nicknamed "Salvation Park" - closed down.
Charities have also recently spoken up about how elephants kept in zoos experience pain and suffering.
In Europe alone, there are 580 elephants held in zoos, including 49 in 11 establishments in the UK - with two housed alone. There are also nearly 300 held in North American zoos.
Born Free says the impact of captivity on their physical and psychological health and welfare means that the majority of elephants in European and North American zoos “develop and display abnormal stereotypic behaviours”.
This includes “compulsive rocking and swaying, as a consequence of long-term psychological damage.” It also warns how “routine chaining is still practised in some European zoos.”
They warned how captive-born elephants in the UK have an average lifespan of just 20 years compared with a lifespan of 50 years in the wild, while 40 per cent of infant elephants in zoos die before the age of five.
Born Free also said numbers in captivity have increased in the last 40 years “through the importation of wild-caught individuals.”
