claimed display area, has been correlated with crest length in both males and females. The existence of these showy monomorphic traits is indicative of intense sexual selection for both sexes. Large-crested adults of both sexes receive higher levels of sexual interest and displays from the opposite sex compared to those with smaller crests. Crested auklets with larger crests are more likely to obtain mates and to form pair bonds earlier. Based on divorce rate and mortality, more than half of individuals find a new mate each year. Female crest length is the primary factor of male mate switching between years. While there is variation in displays across populations, crested auklet crests and plume ornaments are consistent in expression within an individual over time. Furthermore, there is little sexual dimorphism or evidence of condition dependence. From studies, it seems to be a survival-neutral ornament. Some studies, however, offer up a functional purpose for these ornaments. One study suggests a link between habitat complexity and facial feathering, where tactile facial elongation helps individuals navigate complex underground crevices. The high density of crested auklet nesting sites can be expected to impose selective pressures on sensory mechanisms. Vocal ornaments Crested auklets have a wide variety of single and complex calls. Billing is "defined as pair courtship with mutual cackling vocal display." It is a crucial part of successful pair formation and becomes harmonious once male and female partners are well acquainted. Trumpet calls are one of the most common advertising calls. The call represents a complex but stereotyped vocal sequence that is linked with a specific visual display. Between individuals, the calls differ in duration and frequency. Calls are primarily performed in males, but can also be seen in females. The call is particularly strong in widowed females. These calls stay stable from year to year, and individuals' specific calls are associated with the maintenance of long-term social bonds between pair mates and between neighbors. This suggests that trumpet calls can be used for both short-term and long-term individual recognition. Recognition of neighboring individuals' calls is advantageous because it minimizes energy expenditure on aggressive displays, and prevents conflict between neighbors and trusted individuals (the "dear enemy phenomenon"). Olfactory ornaments Crested auklets have a distinctive citrus-like plumage odor. The scent is released when there is ruffling of feathers on the nape and upper back of the individual from threat, trumpeting, or billing displays. The cloud