Figure 9.14 Mating systems. Promiscuity occurs in species of outcrossing plants such as the prairie sunflower (Helianthus petiolaris). Polygyny exists when a male mates with several females, as in elk (Cervus canadensis). Polyandry occurs when a female mates with multiple males, as is the case for the western toad (Anaxyrus boreas). Monogamy for life was thought to be the rule in 90 percent of all birds, as in the sandhill crane (Grus canadensis). However, recent genetic analyses have confirmed that most bird species actually participate in extra-pair copulations.