| Same-sex copulation and bonding are common in hundreds of species, from bonobo apes to gulls. |
| Each male possesses two intromittent organs, one on either side of the body, only one of which is everted during a single copulation. |
| During copulation, the female transfers unfertilized eggs to the male's ventral surface, where fertilization takes place. |
| In this species, long-tailed males are preferred by females both to form a pair bond and to engage in extrapair copulations. |
| Male mosquitofish do not court and copulations result exclusively from males forcibly inseminating females. |
| The birds were fully habituated, and most copulations were observed at 5 m distance. |
