Elephant sex wars

Older bull elephants are more successful at siring offspring and help keep younger males in line but may still be losing out to cunning young rivals, Oxford University scientists have found. The scientists were investigating the mysterious world of elephant sexual behaviour, when 6-tonne male elephants enter a period of heightened sexual excitement and aggression called ‘musth’...

‘Scientists have long been puzzled by the role of musth in the breeding strategies of male and female elephants, especially as many females appear initially to be frightened by overly aggressive bulls,’ said Fritz Vollrath of Oxford University’s Department of Zoology, co-author of the study published in this month's  Behavioural Ecology.

The researchers found that the bulls with the highest reproductive success were between 30 and 45 years old (in the wild elephants can live to over 60 years old). Yet while three older males (44, 40 and 36 years-old) were the most successful fathers these three still only sired less than 20% of those calves whose paternity could be accurately determined. This is in marked contrast to many other mammal populations where alpha males dominate the breeding process – an individual alpha male elephant seal, for instance, will typically sire 50% of the offspring within a group.

‘Our big surprise came when we found that young male elephants in their twenties, which we thought were excluded from breeding by more mature males, actually do successfully father around 20% of calves. And these young males were not in musth,’ said Professor Vollrath. ‘Our research suggests that younger males have developed a sneaky low-profile, ‘non-musth’ strategy to avoid conflict with the larger dominant bulls.’

The relatively high breeding success of these young males is especially surprising because it also goes against observations that females in oestrous enlist the protection of older musth bulls to guard them from groups of young males who would otherwise constantly harass them with their attempts to mate.

However, young males should watch out, when they hit full maturity at 30 their reproductive success drops dramatically for a few years. ‘We’re not exactly sure why this is,’ said Henrik Rasmussen, lead author of the work, ‘but it’s around that time that males mature, reach their full size, and begin expressing musth. Perhaps they need to learn new tactics to fully exploit the chemical signals given off during musth, or perhaps the dominant old musth bulls may be more likely to view these newly matured males as a threat and drive them away from groups of receptive females.’

The findings could have important implications for elephant conservation especially as ivory poachers target older bull elephants. Removing the older males would lead to increased harassment of females and to young males going into musth earlier, as the non-musth strategy becomes less attractive. The observations also suggest that at some time in the past elephant society could have been rather different, perhaps more like other mammal populations where alpha males dominate the breeding process.

Fritz Vollrath, Henrik Rasmussen and Iain Douglas-Hamilton of the Department of Zoology led the work at Oxford.

All three are currently working in Kenya where the original research was done under the auspices of the UK charity Save the Elephants.

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