Control measures have been widely employed to limit the growth of elephant populations in South Africa. Whilst the efficacy of these measures has been monitored closely, there has been little investigation into the behavioural implications of control measures for elephants. In a study published today, Heike Zitzer and I summarised 5 years of observations to understand how vasectomies affect male elephant behaviour.
WHY CONTROL ELEPHANT POPULATIONS?
The need to control elephant populations is a controversial issue. Of course, in an ideal world, there would be no need. In South Africa however, elephants are largely confined to small, fenced reserves. These reserves have provided relative safety from the onslaught of poaching in recent decades. In combination with fences, which eliminate the ability of elephants to disperse, elephant densities in these reserves have increased. Constant high densities of elephants in an area have been linked to directional changes in vegetative communities, with ultimate implications for biodiversity. As a result, reserve managers have sought to control elephant populations.
Initially, culling (killing) was the preferred means of immediately and significantly reducing the number of elephants. However, growing ethical concerns for the welfare of remaining elephants and public pressure prevailed, and the practice of culling ceased in the mid-1990s (although it should be noted that culling was re-established as a last-resort in 2008). Translocations then took over, moving elephants from reserves experiencing high elephant densities to those with small or no existing populations. During the first translocations, only young elephants orphaned during culling operations were translocated, but again ethical concerns arose, and soon family units were moved in their entirety. In the short-term , translocations were deemed a success: elephant densities in the source reserve were reduced and elephant populations were re-established across many parts of their historic range. However, over time the source population recovered and reserves willing to accommodate translocated elephants soon themselves became saturated.
In the following years, focus turned from reducing elephant numbers to limiting elephant population growth and several contraceptive options became available:
- Porcine zona pellucida (pZP) prevents egg fertilisation in female elephants
- Gonadotropin-releasing hormone (GnRH) prevents sperm development and limits the secretion of testosterone in males
- GnRH also prevents follicle development and ovulation in female elephants
- Vasectomies of male elephants to prevent the release of sperm during mating
Both pZP and GnRH require regular treatments via darting, causing high levels of stress and ongoing costs. GnRH has also been documented to alter the behaviour of male elephants (read here). We believe vasectomies overcome many of the issues associated with hormonal treatments…
During an elephant vasectomy, laparoscopic techniques (key-hole surgery) are used to remove a section of the vas deferens (or sperm duct). Importantly, everything else is left intact. This means the testes themselves and the associated tissue remain and maintain normal hormonal function. The technique was first used in elephants in 2004 and was initially lengthy, taking over 4 hours, and required the specialised skills of the Disney vets. Over time however, efficiencies have improved so that treatment now takes less than an hour and local South African vets have been trained in the procedure.
The veterinary procedure itself and the successful recovery of treated individuals has been well documented (see here), but whilst it is expected that vasectomies have no long-term impacts on male behaviour, this expectation has yet to be formally investigated. In our study published today in Bothalia, we report results from the behavioural monitoring of seven vasectomised elephants between 2011 and 2016.
Male elephants and their behaviour play an important role in elephant society. We identified three behavioural aspects we deemed important in male elephant society and recorded these behaviours over the study period:
- The occurrence of musth – musth is a state of elevated testosterone in male elephants associated with a heightened sexual drive and aggression. During musth, males seek out receptive females with which to mate. Older musth males suppress musth in younger males, preventing misdirected aggression and delinquent behaviour. We observed signs of musth in five of the seven vasectomised males confirming that vasectomies do not alter testosterone production.
2. Association with females – despite leaving their family group around 12 years of age, adult males continue to spend a proportion of their time associating with female groups, especially when females are in oestrus. The study males spent roughly half of their time in mixed-sex groups. This is quite a large proportion of time and is possibly because population control reduces birth rates and means female elephants cycle more frequently through oestrus, thus attracting more male attention.
3. Dominance hierarchy – dominance hierarchies in male elephants are linear and age-structured, so that the oldest and largest male is the most dominant. Dominant individuals are afforded the best access to females and so sire most offspring. Using Landau’s linearity index we determined that the dominance hierarchy in vasectomised males was as expected. This was maintained when including non-treated sub-adult males in the analysis, who fell below all older vasectomised males in line with the age-structured hierarchy. Importantly, this means older vasectomised males will continue to restrict access of younger non-treated males to females, maintaining the low birth rates and the long-term efficacy of vasectomies.
Our results confirm expectations that vasectomies do not alter important male elephant behaviour. Given that vasectomies effectively reduce elephant population growth whilst crucially maintaining normal behaviour, we conclude that vasectomies can be used in similar fenced reserves wishing to limit elephant population growth. Additionally, given the need for repeated treatments, ongoing costs and behavioural changes associated with pZP and GnRH, we believe vasectomies are preferable to these alternative contraceptives.
We recommend that further work is required to understand the impacts of vasectomies, and the resulting low birth rates, on female elephant behaviour. It will also be important to monitor the long-term ability of vasectomies to maintain reduced population growth as young, non-treated males become sexually mature.
You can find the full publication here: https://doi.org/10.4102/abc.v48i2.2313