Two female brown bears at Whipsnade Zoo have been euthanised after strong winds felled a tree and created a bridge to the boar enclosure.
ZSL say they are carrying out a full investigation into the incident which happened on Friday morning and saw the bears able to clamber into the neighbouring wild boar enclosure where a male boar was attacked.
Chief curator Malcolm Fitzpatrick said tranquilising the two bears hadn't been an option and immediate intervention had been required for safety reasons
In a message sent to staff, he said he wanted to give a clear explanation over what had taken place.
He said: "Today has been an incredibly upsetting and difficult day for ZSL Whipsnade Zoo, and I wanted to be the one to share some sad news with you.
"Due to strong winds this morning, a tree fell in such a way that it formed a ‘bridge’ between the fence of our brown bear enclosure and the fence of the neighbouring wild boar enclosure. This allowed two of our female brown bears to cross into the wild boar enclosure, where they attacked the male boar.
"One of our zookeepers spotted the breach, and immediately implemented our emergency procedures and protocols. As brown bears are strong and dangerous predators, our first priority is safety – we must quickly make decisions informed by our experience and expertise to protect our people, guests and our other animals."
He continued: "Our experienced zookeepers, who were on the scene within minutes, promptly assessed the situation and agreed the only option was to euthanise the bears. No-one wants to be the one to make that call, but when there’s an immediate threat to human life, the decision is made for you. The colleagues involved today have experienced the dreadful situation that every vet and keeper thoroughly trains for, but hopes will never come to pass.
"I ask you to support them in the coming weeks as they come to terms with today’s events. I expect some of you may read this and wonder why we didn’t use a tranquiliser to sedate the bears, and the short answer is that it simply wouldn’t have worked.
"Despite how it often looks on TV, a tranquiliser can take at least 20 minutes to work during which time the animals can become unpredictable and aggressive as adrenaline is coursing through them. That’s a risk we couldn’t take. We had to intervene immediately to ensure the bears didn’t get out of the boar enclosure, which has a low fence."
Mr Fitzpatrick said a third brown bear had not left her enclosure during the incident. He said: "She was called to her indoor dens and secured, which meant that once we knew that the situation was safe, our vets could examine the injured boar and we were able to remove the fallen tree.
"As zookeepers and animal carers, this situation is something we train to deal with through regular, rigorous drills – but one that we always hope we’ll never have to face. I’m devastated by the outcome of this morning’s incident, but I’m confident that our actions prevented any further loss of life.
"We will of course be conducting a full investigation into this incident, so we can do everything in our power to ensure nothing like this happens again. For now, my priority is looking after the people involved, and the welfare of our affected animals.
"You will know the close relationship our keepers have to the animals they look after, and therefore the impact of today’s events on them. I know that all colleagues at Whipsnade and across ZSL will extend their sympathies to the team for this shared loss."