A fox chewed a hole in a supposedly predator-proof metal fence before killing 25 flamingos and hurting three others at a Washington zoo.

Keepers at the National Zoo made the macabre discovery when they entered the enclosure, which housed 74 of the wading birds, earlier this week.

A northern pintail duck was also killed by the wild fox, believed to have come from the neighbouring Rock Creek Park.

It is the latest in a string of fox-related incidents in the nation’s capital.

Last month, a rapid red fox attacked a politician, who fought it off with an umbrella.

And Capitol Police have received multiple reports of “aggressive fox encounters on or near the grounds of the US Capitol”, including at the nearby US Botanic Garden.

The zoo attack is the worst such incident there for 20 years.

In 2002 and 2003, a string of fox raids led to the deaths of more than a dozen ducks, a peacock and an elderly bald eagle.

Zoo officials instituted new security measures in response to those attacks and those barriers have largely held firm – until now.

The attraction’s bird house is closed to the public for long-term renovations and the flock mainly lives in a 9,750-square-foot yard with a barn and a heated pool.

The area was last inspected on Sunday at around 2.30pm, bosses said.

When staff returned early on Monday morning, they found more than two dozen dead birds and a “new softball-sized hole in the heavy-duty metal mesh that surrounds the outdoor yard”, according to a statement.

Zoo workers also briefly spotted the fox – which escaped – in the outdoor area.

To a fox, a flamingo is “like a chicken with longer legs and a different colour”, Dan Rauch, the city’s wildlife biologist, told The Washington Post.

The ones at the zoo have their wings clipped and cannot fly.

Brandie Smith, the zoo’s director, called the carnage “a heartbreaking loss for us and everyone who cares about our animals”.

She said the fencing and other protective measures were being assessed and upgraded to prevent similar break-ins.

“Our focus now is on the well-being of the remaining flock and fortifying our habitats,” she said.

The birds, formally known as American or Caribbean flamingos, are instantly recognisable from their long stilted legs and distinctive pink hue.

The remaining flamingos have been moved to an indoor enclosure and the injured birds are being treated by the zoo’s veterinary staff.

The mesh fencing is specifically designed to prevent being chewed through by predators and “dig barriers” are also there to block any attempt to burrow under the fence.

The fencing was last replaced in 2017 and had passed all previous safety inspections.

Now the zoo is boosting security again — reinforcing the mesh barriers, setting live traps around the outdoor yard and installing movement-triggered cameras to photograph any nocturnal activity.