Zeenat captured: How wild animals are tranquilised

The moral shift

Until the early 20th century when a “code of catching” was developed, commercial animal catchers either chased and lassoed herbivores or used various types of traps and pitfalls. Things often got bloody as elephant or rhino mothers had to be slaughtered to take away calves which were high in demand.

The need for more efficient and pain-free methods of wildlife capture was fuelled by a shift in the spirit of the time.

In 1896, the British Army adopted what was called Dum-dum bullets, named after the Dum Dum gun factory near Calcutta, where they were first manufactured. These bullets expanded on penetration, tearing tissues and splintering bones. After the Hague Peace Convention banned Dum-dum bullets in 1899, moral debates on the prevention of pain led to experiments such as ‘narcotic bullets’ (1912) which carried a small dose of morphine to kill ‘painlessly’.

From there, the seemingly counter-intuitive leap to “shoot animals alive instead of dead” took another decade and a half, when American naturalist Captain Barnett Harris arrived in South Africa in 1928 with “mercy bullets” — a hypodermic needle filled with chemicals at its base.

The breakthrough

It is speculated that Harris’s bullet was covered with curare — a neuromuscular blocker derived from tree bark, and used on blow-dart tips by South American tribes to paralyse and catch animals. In 1929, he used “mercy bullets” to capture one rhino alive but killed two others in the process.

In 1956, the breakthrough that lifted Harris’s rudimentary design to the realm of practicality was the invention of disposable plastic syringes by Colin Murdoch, a New Zealand pharmacist and veterinarian. With this, Murdoch designed a tranquiliser gun with interchangeable barrels for different calibre syringe projectiles, and a dial to choose from 32 positions.

A modern-day tranquiliser gun propels the dart — a ballistic syringe filled with drug and tipped with a hypodermic needle — using compressed CO2 gas. A tuft of feather as a tailpiece stabilises the dart in flight. The needle is designed with a barb to hang on upon penetration and allow complete release of the full dose of drugs just under the skin.

The drugs

By the mid-1960s, Murdoch’s dart gun was recognised as the most acceptable and efficient method of capturing wild animals. Around that time, British veterinary scientist Dr Antonie Harthoorn and South African conservationist Ian Player developed M99 or etorphine, an opioid stronger than morphine, and still used widely to immobilise elephants and other large mammals.

Before this invention, wild animals were immobilised using neuromuscular blockers or paralytic drugs. Paralytic drugs have a very low safety threshold and high mortality rate as dosage errors of even 10% can lead to no effect (under-dosing) or death (overdosing). Moreover, these drugs did not affect the brain, leaving paralysed animals aware of their surroundings, pain, and the resulting stress.

Modern alpha-adrenergic tranquilisers, such as Xylazine, are strong sedatives which can be completely reversed with antidotes. By themselves, these drugs can heavily sedate animals, particularly ungulates, but external stimulation can disrupt such spells, risking sudden attacks. That is why Xylazine is usually combined with a dissociative anaesthetic, particularly Ketamine, to ensure extended immobility.

The combination is doubly useful because, on its own, Ketamine tends to trigger rough inductions and recoveries. However, the increasing misuse of both Xylazine (as Tranq) and Ketamine (as a date-rape drug) has restricted the availability and usage of this very popular combination for wildlife sedation. Telazol, a premixed ready-to-use combination of Tiletamine and zolazepam, is gaining currency as a substitute.

The delivery

Having a primed dart gun and the right drugs at hand cannot itself ensure a successful sedation. To deliver the remote injection, the target animal has to be traced and tracked to a suitable location. Distance is a crucial factor because the effective shooting range of a dart gun, depending on the make and the size of the dart used, does not exceed 200 ft.

Tracking and approaching a free-ranging wild animal is an art few can master. But getting reasonably close, typically within 50 ft for tigers, is not good enough if vegetation does not allow a clear view of the target. Even a blade of grass can deflect a dart made of polycarbonate.

The next challenge is to assess the right dose — a factor of the target animal’s weight. Telling the weight of a tiger or an elephant, within a narrow band of error, just by looking at the animal from a distance takes a lot of experience. But this is crucial because under or overdosing can endanger lives — either of the captors or the animal.

Once sedated, the protocol is fairly simple. The animal’s eyes are covered to reduce stimulants and constant effort, like fanning or applying wet cloths, is made to keep its body temperature under control. The antidote is injected on completion of the mission or prematurely at any sign of distress.