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. 2020 Sep 3;10(1):13996.
doi: 10.1038/s41598-020-70682-y.

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

Connie R B Allen  1 , Lauren J N Brent  2 , Thatayaone Motsentwa  3   4 , Michael N Weiss  2 , Darren P Croft  2
Affiliations

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

Connie R B Allen et al. Sci Rep. .

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.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
Adolescent males were less likely to travel alone than expected by chance. Observed probabilities of lone travel for the different age classes of male elephants (blue squares), plotted against permuted probabilities of lone travel (boxplots with median, interquartile range, minimum and maximum values). Observed probability for ages: 10–15 = 0.087, 95% CI random = (0.141–0.266), p = 0.001; 16–20 = 0.153, 95% CI random = (0.166–0.232), p = 0.010; 21–25 = 0.239, 95% CI random = (0.156–0.246), p = 0.105; 26+  = 0.272, 95% CI random = (0.154–0.248), p = 0.004.
Figure 2
Figure 2
Probabilities of elephants occupying certain positions within all-male groups. Blue squares represent observed probabilities of occupying a certain position against box plots (with median, interquartile range, minimum and maximum values) of randomly permuted probabilities. (a) Older mature males were more likely to lead groups than expected by chance. Observed probability for ages: 10–15 = 0.097, 95% CI random = (0.128–0.277), p = 0.004; 16–20 = 0.167, 95% CI random = (0.187–0.270), p = 0.005; 21–25 = 0.313, 95% CI random = (0.194–0.312), p = 0.045; 26+  = 0.333, 95% CI random = (0.180–0.305), p = 0.004. (b) Adult males were less likely to occupy the middle position in traveling groups, and adolescents more likely than expected by chance. Observed probability for ages: 10–15 = 0.759, 95% CI random = (0.570–0.736), p = 0.012; 16–20 = 0.715, 95% CI random = (0.577–0.663), p < 0.001; 21–25 = 0.510, 95% CI random = (0.518–0.655), p = 0.028; 26+  = 0.412, 95% CI random = (0.511–0.654), p < 0.001. (c) Males of no age-class were more or less likely compared to chance to occupy the rear of traveling groups. All observed probabilities (blue squares) fell within range of randomly permuted probabilities of occupying the rear of groups (boxplots).
Figure 3
Figure 3
(a) Locations of sampled elephant pathways (orange lines) leading to the Boteti river during the course of the study. Dark green represents the MPNP protected area, and light green unprotected land, dominated by human activities, cattle and arable farming. Aside from one functioning water hole, approximately 12 km northwest of the river, the river was the only permanent water source for wildlife in the area during this study. (b) Examples of images from camera traps (set to record video) of groups of elephants walking in a single file down the pathway. (c) Example images of elephant pathways in the MPNP.
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