Various species of dolphin have been known to engage in sexual behavior up to and including copulation with dolphins of other species. Sexual encounters may be violent, with male dolphins sometimes showing aggressive behavior towards both females and other males. Male dolphins may also work together and attempt to herd females in estrus, keeping the females by their side by means of both physical aggression and intimidation, to increase their chances of reproductive success. Occasionally, dolphins behave sexually towards other animals, including humans.