Data for: Molt timing and duration of northern elephant seals

Life history timing influences many ecosystem processes including predator-prey interactions, information transfer, disease transmission, ecosystem services, and resource subsidies. Many animals and plants have species-typical annual cycles, but individuals vary in their exact timing of life history events. However, quantifying individual variation in the timing and duration of life history events requires longitudinal sampling and may necessitate advanced analytical techniques if observations are imperfect or asynchrony is prevalent. Our goal was to examine factors that influence variation in molt duration and timing across individual northern elephant seals (Mirounga angustirostris). We quantified the onset and progression of fur loss in 1,178 individual seals over seven years. We found a wide range of molt start dates (95% interval spanning 60.1 days within a single age-sex category) and rapid molt progression (6.0 days in adult females and 10.8 and 10.3 days in juvenile females and males, respectively) with high molt asynchrony (only 20% of individuals in the population molting at the same time). Individual variation in the timing of the molt within age-sex categories was much larger than between categories: 94% of the variation in haul-out duration, 74% of variation in molt start date, and 59% of variation in molt duration was among individuals within age-sex categories. Finally, we discovered that individuals arriving late for the molt spent less time on the beach than earlier arrivers, which allowed them to catch up if they fell behind in their annual cycles. These findings emphasize the importance of quantifying individual variation in critical life history events.