 Little is known about the social structure of slow lorises , but they generally spend most of the night foraging alone . Individuals sleep during the day , usually alone but occasionally with other slow lorises . Home ranges of adults may significantly overlap , and those of males are generally larger than those of females . In the absence of direct studies of the genus , primatologist Simon Bearder speculated that slow loris social behavior is similar to that of the potto , another slow @-@ moving nocturnal primate . Such a social system is distinguished by a lack of matriarchy and by factors that allow the slow loris to remain inconspicuous and minimize energy expenditure . Vocal exchanges and alarm calls are limited ; scent marking with urine is the dominant form of communication . Adult males are highly territorial and are aggressive towards other males . Vocalizations include an affiliative ( friendly ) call krik , and a louder call resembling a crow 's caw . When disturbed , slow lorises can also produce a low buzzing hiss or growl . To make contact with other individuals , they emit a single high @-@ pitched rising tone , and females use a high whistle when in estrus . 
