Data from: Revised age estimates for Northern Resident killer whales (Orcinus orca) based on observed life-history events and demographic discounting

Long-term field studies have been invaluable in the study of ecology and
evolution; however, for particularly long-lived species, even long-term
studies often rely on estimated ages, for example when investigating
demographic processes. One approach is to estimate unknown birth dates
from the known timing of other life-history events. Building on previous
methods, we update estimation techniques for Northern Resident killer
whales (NRKW; Orcinus orca) as part of an ongoing long-term study that
began in 1973. Despite almost 50 years of observation, many individuals
were born before records began, and detailed understanding of NRKW life
history relies on estimated ages. Our age estimation approach incorporates
new data from photo-identification surveys into a framework that relies on
accrued knowledge of demographic rates from known-age individuals. We use
Bayes’ law to determine conditional probability distributions from
age-at-event data, incorporating mathematical descriptions of demographic
patterns parameterised from the data. Key to our approach is the
discounting of higher age estimates due to the increasing likelihood of
mortality with age, a pattern not previously taken into account for NRKWs.
We estimate ages for multiple age and sex classes of individuals, using
related but tailored approaches, and we incorporate uncertainty into our
estimates. Our revised age estimates suggest that individuals are often
younger than previously thought (3.5 years on average across 73
individuals; range: 0-15 years). Moreover, the largest discrepancies
appear for mothers with offspring at the onset of the study, a class of
individuals instrumental for investigating menopause in killer whales –
one of the few species other than humans known to exhibit this
life-history feature. Our results will ultimately enable a refined
understanding of the evolutionary forces that produce such patterns. We
discuss the implications of our findings for the study of resident killer
whales and for age estimation in other long-lived animals.