Allegedly…
In of the UK’s ZOO, two Gibbons escaped from their enclosure. It happened during the visiting hours with many visitors in the area.
The working personnel followed the strict company rules and they evacuated the whole ZOO immediately. When the visitors left, they found and caught one of the two Gibbons. They caught the other one only a few hours later.
Gibbons are primates and, in general, they are not considered to be dangerous to people. However, when they are stressed or when they feel in danger, they could get aggressive and attack.

This incident happened on the first day when the ZOO opened after two weeks. It had been closed due to avian flu.
enclosure /ɪnˈkləʊʒə(r)/ – oplotený pozemok, výbeh
in general /ɪn ˈdʒenrəl/ – vo všeobecnosti
consider /kənˈsɪdə(r)/ – považovať (za)
avian flu /ˌeɪviən ˈfluː/ = bird flu – vtáčia chrípka