According to a paper entitled Fellatio by Fruit Bats Prolongs Copulation Time, published in October 2009, research in China had identified the fruit bat as the only creature other than the human in which the female uses oral stimulation of the male to prolong sexual activity.
The researchers comment that bonobo monkeys have been documented as indulging in oral sex, but usually as play behaviour among young males.
By contrast, the female fruit bat licks the base of the male genitals while copulation takes place, and studies showed that licking had the result of prolonging the sexual encounter. In fact the length of time C that copulation lasted in seconds was given by the formula:
C = 101.24 + 6.22L
where L was the number of seconds spent licking. In other words, every second of licking prolonged copulation by just over six seconds.