Page "Sexual intercourse" Paragraph 4

Sexual intercourse between non-human animals is more often referred to as copulation ; for most, mating and copulation occurs at the point of estrus ( the most fertile period of time in the female's reproductive cycle ), which increases the chances of successful impregnation.

However, bonobos, dolphins, and chimpanzees are known to engage in sexual intercourse even when the female is not in estrus, and to engage in sex acts with same-sex partners.

Like humans engaging in sex primarily for pleasure, this behavior in the above mentioned animals is also presumed to be for pleasure, and a contributing factor to strengthening their social bonds.