ESM Figures and Tables from Individual variation in life history timing: synchronous presence, asynchronous events and phenological compensation in a wild mammal

Many animals and plants have species-typical annual cycles, but individuals vary in their timing of life history events. Individual variation in fur replacement (molt) timing is poorly understood in mammals due to the challenge of repeated observations and longitudinal sampling. We examined factors that influence variation in molt duration and timing among elephant seals (Mirounga angustirostris). We quantified the onset and progression of fur loss in 1178 individuals. We found that an exceptionally rapid visible molt (7 days, the shortest of any mammals or birds), and a wide range of molt start dates (spanning 6–10× the event duration) facilitated high asynchrony across individuals (only 20% of individuals in the population molting at the same time). Some of the variation was due to reproductive state, as reproductively mature females that skipped a breeding season molted a week earlier than reproductive females. Moreover, individual variation in timing and duration within age-sex categories far outweighed (76–80%) variation among age-sex categories. Individuals arriving at the end of the molt season spent 50% less time on the beach, which allowed them to catch up in their annual cycles and reduce population-level variance during breeding. These findings underscore the importance of individual variation in annual cycles.