In long-lived social species, older individuals can provide fitness benefits to their groupmates through the imparting of ecological knowledge. Research in this area has largely focused on females in matrilineal societies where, for example, older female African savannah elephants (Loxodonta africana) are most effective at making decisions crucial to herd survival, and old post-reproductive female resident killer whales (Orcinus orca) lead collective movements in hunting grounds. in contrast, little is known about the role of older males as leaders in long-lived social species. By analysing leadership patterns of all-male African savannah elephant traveling groups along elephant pathways in Makgadikgadi pans national park, Botswana, we found that the oldest males were more likely to lead collective movements. our results challenge the assumption that older male elephants are redundant in the population and raise concerns over the biased removal of old bulls that currently occurs in both legal trophy hunting and illegal poaching. Selective harvesting of older males could have detrimental effects on the wider elephant society through loss of leaders crucial to younger male navigation in unknown, risky environments. During coordinated group movements certain individuals can consistently arise as "leaders" with a regular influence over group decisions, with high dominance rank 1 , bold temperament 2 and greater age (often associated with enhanced knowledge or experience 3) noted as common traits characterising leaders (for review, see 4). Whilst in some cases leadership can be a passive process, a consequence of simple consensus decisions to maintain group cohesion 5 , in other cases leaders actively communicate their intent to recruit followers 6. In long-lived species, older individuals often respond more appropriately to complex, changing environments 7,8 , providing substantial fitness benefits to younger group mates. For example, older matriarchs are more effective at mobilising groups in response to predation threats and conspecifics in female African savannah elephants (Loxodonta africana) 8,9 , Similarly, in resident killer whale (Orcinus orca) groups there is a greater reliance on older, post-menopausal females as leaders of hunting groups in years of low salmon abundance 10. Non-human research in this area has tended to focus on females and less attention has been given to the potential for old males to act as repositories of ecological knowledge and leaders in long-lived social species. In many social mammals, males are often assumed to be replaceable because they are typically the dispersing sex 11 , and old males may be reproductively redundant, which is commonly used as an argument to support the legal trophy hunting of old males in many species 12,13. This combined with desirable features such as larger body size and ornaments, leads to selective harvesting of older males in many species, including the African savannah elephant 14. However, there is no reason to believe there would be sex-based differe...

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