Behavioural changes of two female zoo-held western lowland gorillas, after the introduction of a silverback male

Behavioural observations of the two female western lowland gorillas (Gorilla gorilla gorilla) composing an all-female group in Artis Royal Zoo (Amsterdam, the Netherlands) were evaluated. The two females had been observed for one-hr periods over a 166- day period, divided into a period before, and a period after the introduction of a new silverback male. Step intervention analysis showed that in both females locomotion and stereotypic behaviour significantly decreased after the introduction of the silverback. In one of the two females the public interaction also decreased significantly.