Abstract
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.
Highlights
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 noted as common traits characterising leaders
We quantify grouping behaviour and patterns of leadership in all-male elephant groups traveling on elephant pathways to and from the Boteti river in the Makgadikgadi Pans National Park (MPNP), Botswana
Are adolescent male elephants less likely to be observed traveling alone? Lone travellers accounted for 20.8% of sightings on elephant pathways (n = 263/1,264)
Summary
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 e xperience3) noted as common traits characterising leaders (for review, s ee[4]). 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 s pecies[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]. Between 25 and 30 years of age, males will experience their first stable ‘musth’, an annual cycle of temporary heightened reproductive state where males seek out females for mating[21], with up to 74% of calves fathered by males in m usth[22] This temporal concentration of male sexual viability reduces intra-sexual conflict between males and opens the opportunity for male-male prosocial interactions among non-musth b ulls[23], including the opportunity for collective travel and information transfer from leaders to followers. There may be a heightened dependency on older males under particular ecological conditions (e.g. greater leadership by older knowledgeable males in the dry season when resources are s carcer[10], or in the wet season when widely spread, unpredictable resources, such as timings of sprouting of vegetation, may require experienced knowledge to locate32), we find that leadership patterns by age were not influenced by the season
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