Importance of old bulls: leaders and followers in collective movements of all-male groups in African savannah elephants (Loxodonta africana)

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. 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...

Seasonality impacts collective movements in a wild group-living bird

“…all members have equal ability to influence where the group goes [59,60];, one individual can decide for the whole group if it has important information (i.e. the older and more knowledgeable elephants show the way [61,62];). The propensity for an individual to lead the group might be a function of both the state of the individual and the environmental conditions, with shared decision-making providing a flexible algorithm for collective action.…”

Effects of Male Age and Female Presence on Male Associations in a Large, Polygynous Mammal in Southern India: The Asian Elephant

“…Older African savannah elephant males (≥36 years of age in their study) were preferred as nearest physical neighbors during associations by males of all ages, based on observations in a bull area in Okavango Delta, Botswana (Evans and Harris, 2008), and have been considered analogous to the knowledgeable matriarchs of female groups in the species (Evans and Harris, 2008). In a bull area in Botswana, older males (≥26 years of age in their study) were more likely to lead all-male group movements than expected by chance, possibly serving as repositories for ecological knowledge (Allen et al, 2020). More generally, preferred association with, and social learning from older, more experienced individuals has been observed in the context of mating behavior (Pereira, 1988;Beecher et al, 1994), and foraging strategies (Rajpurohit et al, 1995;Biro et al, 2003) in other species.…”

“…African savannah elephant males nevertheless exhibit complex relationships, with males preferring to associate with age-peers (Chiyo et al, 2011;Goldenberg et al, 2014 -in the case of sexually inactive males) and related males (Chiyo et al, 2011). Male associations also facilitate social learning from older males (Chiyo et al, 2012), which may be preferred associates or more central to male society than young males and lead traveling male groups (Evans and Harris, 2008;Chiyo et al, 2011;Allen et al, 2020;Murphy et al, 2020). Thus, temporary all-male groups in African savannah elephants seem to provide an opportunity to spar and test strengths, and also possibly for younger males to learn from knowledgeable, older males.…”

Function of Trunk-Mediated “Greeting” Behaviours between Male African Elephants: Insights from Choice of Partners

“…We were first interested in exploring how differences in age affect the rate at which elephants perform trunk-to-SEO behaviours, hypothesising that (i) males of different ages will perform trunk-to-SEO behaviours at divergent rates. Adolescents are in general more sociable than adult male African elephants; they are found in larger groups [ 28 ], and are less likely to travel alone [ 44 ]. If adolescents perform more trunk-to-SEO behaviours compared to adults, it may be that these behaviours are used to facilitate further social connections and interactions, or to obtain information about other males in the male social network to which adolescents are more recently dispersed and less stably established in [ 27 , 31 ].…”