No, loons do not mate for life. Far from it! Since loons commonly live 20 years or more and territorial takeover is frequent, a typical loon will have multiple mates during its lifetime. Mating for life does not make sense evolutionarily. Instead, each loon behaves so as to maximize its own reproductive success (i.e. the number of young it produces). Hence, a breeder that loses its mate to death or territorial takeover pairs as quickly as possible with another loon of the opposite sex and gets on with its life. Similarly, a loon that is itself evicted from a territory begins immediately to look for a new territory (and mate) nearby so that it can resume breeding. Still, loons are genetically monogamous; that is, the young reared together by a male and female are the true genetic offspring of both pair members.