Hi, Apparently, with plenty of space and no other howler monkeys around, there was no need to check on to determine the whereabouts of their competitors. At the sanctuary, keepers now use recorded howler sounds from a distance so that the monkeys feel the need to make the territorial calls as they would do in the wild. In the future when the population grows, there will be no need for the recording because the howler monkeys will have more reason to check in with to establish a realtionship with with the neighbors to define their own territories.
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