How vasectomy affects elephant behaviour in the longer term

Elephant

In many reserves elephant population size has already grown to, or exceeds, the carrying capacity of the reserve

Elephant population control has become a necessary part of game reserve management because high densities of elephants in fenced reserves can have a permanent, negative impact on vegetation.

Contraception has been promoted as the most effective control method for discrete elephant populations. Ideally, contraception should be applied to some, but not all, females as a means of reducing breeding, with care being taken to maintain a full age distribution within the herd.

However, in many reserves, elephant population size has already grown to, or exceeds, the carrying capacity of the reserve, meaning that breeding should be halted until elephant densities have been reduced (eg by moving perimeter fences to incorporate new land into the reserve).

Because there are more females than males, female contraception is often prohibitively costly, meaning that male contraception may be more practical.

The importance of musth

Dominance among male elephants is generally associated with age and body size, with dominant individuals having preferential access to fertile females. Sexual activity and aggression in male African elephants are associated with musth, a physiological condition resulting in heightened aggression and increases in testosterone production.

Although males show signs of sexual activity from around 12-15 years old, male elephants are not fully mature until they reach 40 years of age.

The duration and intensity of musth in younger male elephants are moderated by hormone suppression from older males within the same population. Hormone suppression is a specific term in which the hormones of one individual are suppressed by the pheromone secretions or behaviour of another individual. In some cases (as with elephants) it is both pheromones and behaviour of older bulls that suppresses the onset of musth in younger bulls. In the absence of older males, younger males can display heightened levels of aggression. Consequently, musth plays a pivotal role in shaping dominance relationships among male elephants. Contraceptive interventions that interfere with the hormones associated with musth are therefore best avoided.

Options

There are two general methods for bull elephant contraception: gonadotropin-releasing hormone (GnRH) suppressant and vasectomies. Despite the invasiveness of the surgical procedure, laparoscopic vasectomy is the preferred method because it prevents conception but does not interfere with musth.

Nevertheless, as vasectomy for bull elephants is a relatively new procedure, little is known about the long-term effects of vasectomies on elephant behaviour. This study aimed to investigate the social interactions of elephants at Pongola Game Reserve following the vasectomies of seven of the eight adult bulls (the dominant male in the population was too large to undergo surgery) in 2008.

Results

As predicted, male dominance rank was significantly correlated with age (rs= -0.97, n=8, p<0.001: Figure 1). All males remained sexually interested in females and although mating did not occur with most males due to their relatively young age, all males directed sexual displays towards females and all but the youngest two males received sexual advances from females. Moreover, male-male dominance interactions occurred at a significantly higher rate when in the presence of females (t= 2.61, df=7, p =0.035). These results suggest that male social and sexual behaviour has not been affected by vasectomy.

We were initially concerned that the higher numbers of cycling females caused by reduced rates of conception would alter male association patterns with female herds because, contrary to natural populations, males were rarely apart from the females. However, it now appears that the primary determinant of patterns of male-female association was the limited space in the reserve, with both sexes independently attempting to access resources rather than male attraction to females. Now that additional space has been made available to the elephants, many of the males spend significant amounts of time alone in other sections of the reserve that also have access to water and preferred food sources.

Figure

Figure 1: Relationship between dominance rank (calculated from patterns of uni-directional aggression, dominance displays and submissive displays) and age of male elephants at Pongola Game Reserve

Population control

The results of this long-term study suggest that vasectomy is a cost-effective, viable way to control elephant populations. A disadvantage is that fully adult males cannot be vasectomised because of the risks of operating on such large animals. Consequently, breeding cannot be entirely halted by vasectomy if there are fully mature males present in the population.

Removing fully mature males or preventing their breeding using hormone suppression is also not recommended because these mature males’ musth is critical for maintaining social order in the population.

Reserves opting for vasectomy as a method of population control should therefore allow limited breeding (by mature bulls) to continue until the vasectomised males have fully matured. Only then should older breeding males be removed from the population.

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3 Responses to “How vasectomy affects elephant behaviour in the longer term”

  1. While I find this article to make an excellent case for the vasectomy of elephants in an overcrowded population, prompted by the sample in which seven of eight bulls in the Pongola Reserve underwent vasectomies, I am inclined to ask whether vasectomies provide an adequete solution to overpopulation when considering the fact that for all intents and purposes vasectomy in elephants is an irreversible process. This makes me wonder whether it is worth reducing a genepool to only one male when a less invasive and more cost-effective procedure such as use of the GnRH vaccine could be implemented instead.

  2. Hi Tabitha

    You raise an extremely valid point and I agree that the situation at Pongola Game Reserve were the study took place it not ideal. I must stress that the best method of elephant contraception is PZP given to females because it is not permanent, and you can change which females receive it in order to maintain genetic diversity in the herd. The problem is that most reserves cannot afford to do this. The alternatives are therefore male contraception or culling. As we know that culling can have disastrous consequences, male contraceptions seems to be better option.

    I can confirm that in the case of Pongola, there is only one fully adult breeding male anyway as the other fully adult male was removed from the population before we became involved in the project. I can also confirm, that due to the ages of the bulls in the reserve and female preference for mature males, breeding would have been restricted to this one male regardless of any contracpetion invtervention.

    The musth of this one remaining male (Ingani) is controlling the onset of musth of the other younger males. The reserve had planned to remove Ingani to completely halt breeding in the reserve. Based on evidence from other reserves such as Pinda, we now know that in the absence of control from older bulls, younger bulls will literally run riot. Pongola therefore has a bit of a problem in that they want to stop breeding in the reserve, but they need the musth of the one remaining older male. As he is too large for a surgical procedure, the only contraceptive method available is GNRH, which as we know, interferes with musth!

    All the reserve can do now, is wait for a few more years until the beta male Shayisha is fully mature and then Ingani could be relocated to another reserve such that breeding would completely stop in Pongola. In the meantime, huge efforts are being made to increase the amount of space available to the elephants by moving perimeter fences.

    As you can see, a very complicated siutation and I hope that this article demonstrates that although vasectomy is an effective method of population control, reserve managers really need to think carefully about using it, because its suitability is heavily affected by the age distribution of males in the population.

  3. Hi Dr Slater

    Thankyou for taking the time to reply, it was very interesting. I suppose our conversation simply highlights, as is already clear, that this is a hugely complex issue and there is no black and white solution to the problem! We can only hope that more people such as yourselves are willing to spend time and money to preserve elephant herds and will continue to do so in the future.

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