(CNN) - London Zoo has come under fire from animal rights groups for restarting adult-only, late-night parties -- despite concerns about drunk guests interfering with the animals or attempting to enter their enclosures.
The venue's "Zoo Nights" are set to run on eight Friday evenings in June and July, and will allow adults to "embrace their youthful sense of awe and wonder," the zoo says.
But a petition calling for their cancellation has been signed 15,000 times and several leading animal rights groups have urged the zoo to reverse the "irresponsible" move.
"This is a recurring event where the zoo is basically turned into a nightclub for the night, with music blaring and alcohol being sold, with no care for the animals," the petition states. "This has to stop," it adds.
The zoo, which says the fears are unfounded, scrapped similar after-hours events in 2015 following a number of reported incidents. One saw a man pour beer over a tiger, while another guest stripped off and attempted to enter the penguin pool, The Guardian reported at the time.
"The presence of visitors tends to stress animals in zoos, whatever the time of day -- so adding more visitors is going to add more stress," Chris Draper, head of Animal Welfare at the Born Free Foundation, which has researched the impact of the nights on animals in the past, told CNN. "Adding more stuff going on late at night adds insult to injury."
"It raises the prospect of bad behavior, if they're adding to music to the mix," Draper said. "These animals are not subjected to music on a daily basis, they're not used to music."
Dismissing the events as irresponsible, Draper said the zoo is sending a message "that it's OK to treat animals as entertainment exhibits."
Two of the UK's largest animal rights groups, the RSPCA and PETA, have also sent statements to CNN that urged the zoo to backtrack.
"Zoos should be responsible for the safety of the animals in their care. Allowing these late-night events to continue does not demonstrate adequate consideration for animal welfare," said Adam Grogan, head of wildlife at the RSPCA.
"Mixing animals with people drinking alcohol can have disastrous results -- a fact that ZSL London Zoo is well aware of yet is deliberately choosing to ignore," PETA UK's Director Elisa Allen added. "To host loud, alcohol-fueled events which cause them fear and distress and even pose a threat of physical harm to them defies belief.
Previously known as Zoo Lates and first reintroduced under the Zoo Nights name in 2017, the events will take place around various animal enclosures, and will feature a crazy golf course, alongside "live acoustic music, animal lanterns and a variety of entertainment."
But the zoo, which charges £20 ($25) for tickets to the nights, said previous reports about incidents during the events were "heavily sensationalized."
"No visitor ever injured an animal, nor got into an animal enclosure," they said in a statement. "We have strict measures in place and animal welfare is always a top priority when planning events. At every Zoo Nights event we have an animal welfare officer present along with our expert zookeepers who care for our animals. We also monitor sound levels and ensure we continuously adhere to all relevant policies."
The annual events served as a valuable fundraising venture for the zoo when they were originally run, with the venue saying they attracted 60,000 attendees over nine nights and generated £500,000 ($630,000) through "PR."
The zoo houses over 20,000 animals within its enclosures.
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