a year. Because mating occurs at sea and males have no copulatory organ, males must hover over females for a successful mating. Mate choice is mutual, but females do have final choice on breeding partner. Crested auklets are highly social during the breeding season, before pair formation, and after pair formation. Within a breeding year, however, crested auklets are monogamous, with only 10% of the population having extra-pair copulations. Partners continue to self-advertise to other birds when they are not incubating. While some of this advertising behavior can be linked to extra-pair mating, it is suggested that continuation of the behavior allows birds to find pairs for the next breeding season. Only 45.5% of birds remain with the same partner in the subsequent breeding season. Both sexes invest highly in parental care; parents share equally in incubating the single egg and raising the chick. Since both sexes are ornamented, crested auklets align with Robert Trivers's parental investment theory, which predicts that with biparental care, mutual choosiness will arise. Sexual selection Crested auklets are unique in their use of optical, vocal, and olfactory signals in mating. Their communicative behavior is more complex and diversified than that of closely related species. There are three general evolutionary mechanisms proposed to address the origin of the elaborate display traits of crested auklets, and of showy mating signals by males in general: Runaway selection: Fisher's theory of runaway sexual selection explains flamboyant traits in males as resulting from a genetic linkage between ornamental traits and a mating preference for such ornaments. Under this model, mating preferences could be spread by arbitrary or even deleterious traits that carry no benefits to fitness, besides sexual selection. The good genes hypothesis: The second mechanism is the good genes or handicap processes, where mating preference focuses on ornamental traits that reflect the health or viability of the individual expressing them. These good genes convey genetic benefits to the offspring. Amotz Zahavi proposed the handicap hypothesis, where he suggests that individuals’ ornamental traits are indicators of good fitness, because they reflect the individual's success in spite of these traits as handicaps. Sensory exploitation: The third proposed mechanism is sexual selection for sensory exploitation, which results in mating preferences that arise due to natural selection for inherent sensory biases. Mutations occur that result in a display trait which exploits the pre-existing sensory bias. Ornamentation Visual ornaments Asserted dominance, with regards to