The UK's biggest zoo has told Newsround they are increasing security patrols for their animals, after an incident at a French zoo.
Poachers broke into a zoo in Paris and killed a rhino for its horn. The zoo's two other rhinos weren't hurt.
ZSL Whipsnade is home to a herd of greater one-horned rhinos and white rhinos.
They're kept in secure enclosures guarded by full time security teams who do regular patrols.
They told us: "Our security teams at ZSL London Zoo and ZSL Whipsnade Zoo are aware of this tragic incident, and will be increasing their on-site patrols."
Rhino horn can be sold illegally in places like China and Vietnam for huge amounts of money.
It's believed this is the first time poachers have targeted a rhino in a European zoo.
Newsround spoke to several other zoos across the UK who told us they're also looking at increasing or reviewing their security measures.