Inter-species sex
See also: Animal hybrid, Sexual imprinting, and Zoophilia
Some animals opportunistically mate with individuals of another species. This is more commonly observed in domesticated species and animals in captivity, possibly because captivity is associated with a decrease in aggression and an increase in sexual receptivity.[66] Nevertheless, animals in the wild have been observed to attempt sexual activity with other species.[67] It is mostly documented among species that belong to the same genus, but sometimes occurs between species of distant taxa.[68] Alfred Kinsey cites reports of sexual activity involving a female eland with an ostrich, a male dog with a chicken, a male monkey with a snake, and a female chimpanzee with a cat.[69]
A 2008 review of the literature found 44 species pairs that had been observed attempting interspecies mating, and 46 species pairs that had completed interspecies matings, not counting cases that had resulted in hybridization. Most were known from laboratory experiments, but field observations had also been made.[68] It may result in fitness loss because of the waste of time, energy, and nutrients.[68]
Male sea otters have been observed forcibly copulating with seals,[70][71] and male seals have been observed forcibly copulating with penguins.[72] Inter-species sexual behavior has also been observed in sea lions.[73] Male grasshoppers of the species Tetrix ceperoi often mount other species of either sex and even flies, but are normally repelled by the larger females.[68] Males of the spider mite species Panonychus citri copulate with female Panonychus mori mites almost as often as with their own species, even though it does not result in reproduction.[68]
The Japanese macaque has been observed attempting to mate with the sika deer.[74]