Mating and remating of least auklets (Aethia pusilla) relative to ornamental traits

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Abstract
We investigated mating patterns of the least auklet, a small monogamous seabird, at St. Paul Island, Alaska, during three breeding seasons. Least auklets mated assortatively with respect to both plumage color, a trait important in status signaling, and tarsus length, an index of body size. Least auklets mated disassortatively with respect to the extent of facial plumes, but neither assortatively nor disassortatively for any other ornamental trait (bill color, bill ornament size). Mate fidelity was lower in least auklets than in some long-lived seabird species; when both members survived to a following year, only about two-thirds of pairs reunited. Nearly half of the auklets paired in 1 year obtained a new mate in the following year, either because of mate disappearance or divorce. Interyear fidelity to mates was related only to male ornamentation; males with larger facial plumes were more likely to reunite with their mates the next year than males with smaller plumes. There were no significant differences in the ornaments of females in reunited and divorced pairs. Pairs that reunited also had significantly lighter plumage than pairs that divorced, and the plumage of males reuniting with their mates was significantly paler than that of divorced males. We conclude that the probability of both divorce and remating in this species is influenced by ornamental traits. Our finding that remating was related to male plumage color and ornaments is consistent with the idea that remating is influenced by female choice. Pairs that reunited also bred earlier in the season and had higher reproductive success than pairs with experienced individuals breeding together for the first time. We also found evidence that failure to breed in a given year increased the probability of subsequent divorce.

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