Are lions monogamous?

No. In this instance I will use the modern use of the word "monogamous" to mean one sexual partner. During estrous (estrus) the female will copulate with a male many times, on average every 25 minutes over four days or more. At the end of estrus they mate less often. As the male's desire wanes, the female "may seek additional partners". Accordingly the female lion, is not monogamous.

photo by imolcho

At this time other males get a chance to mate with this lioness indicating that male lions "share" females. Accordingly male lions are not monogamous either.

The larger more elderly males have more success in mating with a female than younger, smaller males. Not all males achieve copulation with a female. Lion prides are made up of related lions.

Associated page: Are cat polygamous?