Methods

Here we use post-reproductive representation (PrR) as a measure for post-reproductive lifespan, which is measured as the proportion of adult female years being lived by post-reproductive females43. While a decline in fertility with age is a general trait among animals44, the long post-reproductive periods, often spanning more than a decade, observed in humans and some toothed whales is a rare trait. Reports of post-reproductive lifespan in other species often reflect individual variation in senescence, rather than a general trait at the population level or are calculated for populations living under artificial conditions often with reduced mortality risk3,45–47. A significant advantage of the PrR measure is that it is a population-level measure that is directly comparable between species or populations with different lengths of lifespan as it is the number of female years lived post-reproductively out of all years lived by females in a given population, while PrR also allows for a test of whether the post reproductive lifespan is significantly larger than what is expected by chance43.
Data type and collection
Long-term photo-identification data have been collected on three killer whale populations with overlapping geographical ranges in the waters off Washington State, the state of Alaska, USA and British Columbia, Canada: Northern resident, Southern resident and Bigg’s killer whales41 (Table 2). Photo-identification studies began in 1972 for Bigg’s, 1973 for Northern residents and 1976 for Southern residents. Data collection were boat-based and during each encounter identification photos of dorsal fins and saddle were obtained from the left side of each whale38,48. Sex was determined based on the pigmentation of the ventral side of genital or mammary slits, the presence of neonates or the size and shape of the dorsal fin of adults41.