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.