Reproductive sexual intercourse between non-human animals is more often termed copulation, and sperm may be introduced into the female’s reproductive tract in non-vaginal ways among the animals, such as by cloacal copulation. For most non-human mammals, mating and copulation occur at the point of estrus (the most fertile period of time in the female’s reproductive cycle), which increases the chances of successful impregnation.[27][28] However, bonobos, dolphins and chimpanzees are known to engage in sexual intercourse regardless of whether or not the female is in estrus, and to engage in sex acts with same-sex partners.[10][29][30][31] Like humans engaging in sexual activity primarily for pleasure,[10] this behavior in the aforementioned animals is also presumed to be for pleasure,[32] and a contributing factor to strengthening their social bonds.[10]