The zoo said the gibbons, Duana, 7, and Samuel, 11, will be confined to their housing units on "Gibbon Island" for three nights a week, after Bristol residents complained that the loud singing that makes up part of the primates' mating ritual has been waking them up in the early morning hours, The Daily Telegraph reported Monday.
Bristol City Council upheld the noise complaints after environmental health officers monitored the singing for several nights.
The gibbons were previously allowed outside whenever they wished through use of a door in their housing unit.
"The gibbons are very noisy at daybreak and in the evening. The female, in particular, makes a very distinctive call," said Phyllis Farmer, a resident who lives near the zoo. "There was no one supervising them after 6 p.m. and they more or less had the run of the place. There is a school very close to the zoo and they must hear them all the time. I wondered if one of the pupils sitting exams might be bright enough to write on his paper that he couldn't concentrate because of the noise."