A novel technique for aging male African elephants (Loxodonta africana) using craniofacial photogrammetry and geometric morphometrics

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.

Consistency and flexibility of character in free-ranging male African elephants across time, age, and social contexts

Post-dispersal male African elephants (Loxodonta africana) live within complex social networks. To quantify the consistency of male elephant character (or personality) within these networks, we employed behavioral repeatability analysis tools across social and environmental contexts. We collected behavioral data from thirty-four individually-identified male elephants at the same waterhole over five field seasons (2007-2011) in Etosha National Park, Namibia. Using repeatability models to assess ten behavioral categories, we found five behaviors (affiliation, aggression, dominance, self-directed anxious, and self-directed comfort) were consistent at the individual level. Some of these behaviors were also repeatable, depending on social context. In particular, the presence of younger males and a keystone male (i.e., the most dominant and socially-integrated individual during our study period) had the biggest impact on adult male behaviors. Surprisingly, the presence of elephants in musth had little impact. Finally, we found that younger individuals were more alike in their overall character profiles than older males, further supporting the hypothesis that male elephants develop unique, yet socially-flexible character types as they age. These results demonstrate that male elephants possess distinct character traits that are also behaviorally adaptable, depending on the social context. Overall, our research further highlights the complexity of male elephant individuality and social dynamics that might be leveraged to improve in-situ and ex-situ management and conservation decisions for the species.

The use of vocal coordination in male African elephant group departures: evidence of active leadership and consensus

Group-living animals engage in coordinated vocalizations to depart from a location as a group, and often, to come to a consensus about the direction of movement. Here, we document for the first time, the use of coordinated vocalizations, the "let's go" rumble, in wild male African elephant group departures from a waterhole. We recorded vocalizations and collected behavioral data as known individuals engaged in these vocal bouts during June-July field seasons in 2005, 2007, 2011, and 2017 at Mushara waterhole within Etosha National Park, Namibia. During departure events, we documented which individuals were involved in the calls, the signature structure of each individual's calls, as well as the ordering of callers, the social status of the callers, and those who initiated departure. The "let's go" rumble was previously described in tight-knit family groups to keep the family together during coordinated departures. Male elephants are described as living in loose social groups, making this finding particularly striking. We found that this vocal coordination occurs in groups of closely associated, highly bonded individuals and rarely occurs between looser associates. The three individuals most likely to initiate the "let's go" rumble bouts were all highly socially integrated, and one of these individuals was also the most dominant overall. This finding suggests that more socially integrated individuals might be more likely to initiate, or lead, a close group of associates in the context of leaving the waterhole, just as a high-ranking female would do in a family group. The fact that many individuals were involved in the vocal bouts, and that departure periods could be shorter, longer, or the same amount of time as pre-departure periods, all suggest that there is consensus with regard to the act of leaving, even though the event was triggered by a lead individual.