LONDON — One man poured beer on a tiger. Another tore off his shirt and attempted to enter the penguin pool. Music blared and drinks flowed.

Those were some of the scenes described during the 2014 season of London Zoo’s late-night adult-only event, which is billed as a way to bring people closer to the animals outside of regular zoo hours and to raise funds for conservation.

General admission tickets for the Friday sessions, which run every summer and are called Zoo Nights, start at 20 pounds, or about $25, and more than £1 million in revenue has been generated since 2017. The funds go toward international conservation programs and efforts to combat the illegal wildlife trade, plastic pollution and habitat loss.

But activists say the mix of alcohol and music at the sessions — this year’s event began on Friday — is detrimental to the animals that serve as the backdrop. Many have called for the sessions to be canceled.