• Physical barrier systems include trenches, bamboo spikes, sharp stones, brick walls, natural material
• Chemical deterrents include capsicum. chillie, pepper  

This is the final part of a two-part series of articles. The first was published in the 13 February issue

Traditional low-cost strategic methods used by farming communities the world over to deter elephants from raiding and damaging croplands include physical barrier based systems and chemical deterrents.

These methods were noted in an article on the ‘Indigenous knowledge to deter elephants damaging croplands’ which was authored by C.S. De Silva and H.K.L.K. Gunasekara (both attached to the Open University's Engineering Technology Faculty's Agricultural and Plantation Engineering Department), and published in the Journal of Intangible Cultural Heritage's Third Volume’s Second Issue, in July of last year (2024).

Physical barrier-based systems

Barriers work on the principle of physically excluding elephants from the crop fields. The method involves putting up physical barriers in the pathways of elephants. 

Trenches

In Asia, trenches are dug along a park boundary or around water points. The concept is to dig a trench that is wide and deep enough so that an elephant cannot step over it (elephants are not able to jump). In some places, trenches are filled with pointed sticks to further deter elephants from crossing. The major drawback with trenches is that, if dug on a slope, they encourage soil erosion. Elephants have also been known to fill them in by kicking soil from the edges into the trench, thereby filling it and enabling them to cross. Trenches require a large initial investment of labour and intensive maintenance (per two African studies).

Covered trenches

Experiments with shallow trenches overlain with branches and leaves have been successful in India. When an elephant treads upon the leaves, it feels the substrate give and fears that it will plunge into a pit, and so, it withdraws. The trench need only be 30 cm deep, but it must be wide enough to prevent an adult bull from stepping right over it. The covering must be well-maintained because once an animal realises that this is a hoax, this tactic will be ineffective. This method requires a great deal of labour and in high rainfall areas, soil erosion may be a problem.

Bamboo spikes

Short lengths of bamboo are sharpened and dug into the ground so that the spike protrudes vertically from the soil. Spikes must be positioned close together and in a wide band so that the elephant can neither step between the spikes, nor step over the entire barrier. Elephants will not tread on the spikes, as they require a large surface area to distribute their weight. In areas where bamboo is readily available, this method would be cost-effective, but the limitations would be the labour and time involved in the construction.

Sharp stones

A barrier of sharp stones is laid out in a broad band and the elephants will avoid crossing them. The method is time-consuming and labour intensive, but, ultimately, cheap and of low maintenance. It would require access to a large number of suitable stones.

Brick walls around water structures

A barrier of bricks is constructed around water structures to prevent elephants from crossing them. Walls need to be at least two large rocks in width, and 1.8 metres high and with a sufficient distance from the water tanks and pumps to prevent elephants reaching the installations from outside the wall.

Barriers with natural material

One of the most common barrier materials is thorn branches. Logs and sticks are also piled up around the edges of fields. In some areas, farmers simply run bark ropes from tree to tree and hang pieces of white cloth from the line. Brightly coloured cloths and plastic are hung from a simple fence at the edge of the fields. Such visual deterrents may have an initial ‘scaring’ value, but it is unlikely that this method would provide any reliable protection. None of these barriers can stop a determined elephant, but, any boundary to a cultivated area creates a psychological barrier that can have some impact. 

The most important aspect is the availability of the materials to build the barriers. The limitation of barriers is that they are generally expensive to construct, require a lot of labour and require high levels of maintenance. Elephants will overcome even the most sophisticated barriers over time. In addition, permanent barriers may not be popular with farmers as they are seen as a restriction on agricultural expansion.

Chemical deterrents

Chemical compounds with potential deterrent capabilities may prove an effective way to deter elephants, either as an unpleasant or painful smell, or as a targeted compound such as a hormone, which creates fear.

Capsicum deterrent

Repellents based on the resin from Capsicum spp. (chillie peppers) have been used to alter animal behaviour for a variety of species, including bears, ungulates, dogs, and humans. The resin contains a chemical found in fruits of Capsicum spp., capsaicin, which is the agent that makes them taste hot. The irritating quality of this stimulation produces a burning sensation that mammals find extremely unpleasant.

Chillie bricks

Chillie bricks are a low-tech technique that evolved from pepper sprays. Working on the same principle that elephants are repelled by capsicum, the chillie bricks only utilise simple, locally available materials. Dry chillie is mixed with elephant or cattle dung and compressed into bricks. The bricks are then sun-dried and burnt at the edge of the fields. The bricks burn slowly and produce a strong-smelling cloud of chillie smoke.

Pepper spray

To extract the capsaicin, peppers are soaked in solvents. The amount of heat in a pepper is measured in Scoville Units (SUs). A very hot pepper measures approximately 30,000 SUs. The capsaicin is mixed with soybean oil and inserted into an aerosol can with a modified spray nozzle (similar to hairspray). The mixture is then pressurised and when the trigger is depressed, an atomised spray cloud is produced. Atomising the capsaicin into a gas cloud makes it an extremely effective irritant. The effects of pepper spray on elephants are far more severe, including temporary blindness which lasts from 15-30 minutes and a burning sensation of the skin which lasts from 45-60 minutes.

Conclusion

Elephants damaging the crop land and the livelihood of poor and rural populations are great problems. Even though there are electric fences to protect croplands and villages, elephants get used to this system and damage the electric fences too. Instead of electric fences, beehive fences will be more useful, and farmers can also gain an additional income from the honey and other products. Buffers of chillie cultivation also deter elephants. 

There are several vegetative barriers using unpalatable crops such as tea, mustard, ginger, oilseed, agave and cacti, sunflower, moringa, and lemon. Medicinal plants such as chamomile, coriander, mint, basil, turmeric, lemongrass and citronella are less attractive to elephants. 

Furthermore, acoustic deterrents such as shooting, bells, noise, tiger growling, and fire are also found as methods to deter elephants. Physical barriers such as trenches, fences and bamboo spikes also deter pachyderms. Several chemical deterrents such as chillie and pepper sprays are also used. Therefore, local communities facing elephants damaging croplands could use any of these low-cost methods available to deter elephants. Since elephants get used to any method very quickly, local communities need to utilise several of these methods.