Conservation and Predatory Behaviour of Tigers


Tiger habitat is continuously shrinking and fragmenting due to anthropogenic pressures. The fragments are more and more isolated- surrounded, and even occupied, by people with very real needs. Increased protection is needed, but the conservation of tigers also required a sound knowledge about its ability to respond to abrupt environmental change and highly altered environments. Having a comprehensive understanding of the tiger’s behavioral flexibility and ecological needs helps us to understand it’s conservation needs. This will help us to take appropriate actions to maintain our largest cats. A study was done by John Seidensticker and Charles McDougal in Nepal’s Chitwan National Park to assess the predatory behavior and the plasticity of tiger prey acquisition.


The predatory behavior of tigers can be divided into three stages- detection of prey, capture, and consumption. Although success is achieved by the tiger when the prey is killed but the process of capturing the prey comes with its own set of risks for the tiger, especially when seizing large prey. Plasticity in prey capture is a key component in the flexible acquisition of resources. Because it is difficult and rare to observe natural acts of tiger predation, this study observed a tiger killing domestic water buffalo (Bubalus bubalis). Schaller, however, separated the process of killing large mammals by lions and tigers into two parts, that is, bringing the prey down, and killing it. The initial contact was a bite on the throat or nape, seizure with the teeth and forepaw, or with both simultaneously. But there also have been instances of the first bite delivered on the prey’s leg or shoulder. 


According to Leyhausen, a cat’s canine teeth strike the cervical vertebrae and insert the tooth between the vertebrae like a wedge and force them apart. This severely severs the spinal cord completely or partially. In this study, there have been differences observed in the method of killing between adult and subadult tigers. Subadults usually killed with a throat bite whereas adults did with a nape bite. Sunquist examined 26 tiger kills to determine the factors which lead to nape bite or throat bite and concluded that when the weight of the prey is more than half of that of the tiger, throat bite is used to kill.


Tigers are plastic in their predatory behavior rather than stereotypic, that is, they do not employ the same methods of exploitation for different resources and in different environments. These variations in hunting down similar-sized prey in similar environments displayed the range of movement options available to tigers to counter various escape maneuvers by the prey. Tigers show a range of behaviors in killing large mammals, that varied with the particular tiger’s size and experience. The nape of animals that tigers kill is usually protected by horns or antlers. Therefore a throat oriented bite makes it easier for the tiger to twist a large prey’s neck and anchor it to the ground. This helps in keeping the sharp horns or antlers pointed away. It also helps tigers kill prey too large for their canine teeth to penetrate to the cervical vertebrae. On the other hand, smaller felids, which capture prey considerably smaller than themselves usually kill the prey by biting into the nape of the animal’s neck. 




Tigers have the largest canines and jaw length amongst all felids. It is found that felid canines are longer and rounder than canid or hyaenid canines. The behavior of killing that the sub-adults learn will also be employed to kill prey in their adult stage to kill very large prey. While tigers are known to kill some of the largest prey available, they are not limited to that and can take prey of varying sizes. 


When the diet of tigers was examined in Chitwan, it was found that they killed prey of a wide range of sizes. Their primary preys were deer and swine (deer and swine constituted 75% of the crude biomass of Chitwan). This indicates that tigers take prey in proportion to availability in terms of biomass. However, tigers were not hunting ungulates based on their abundance in number in the environment. Tigers usually took larger prey, Cervus unicolor and Sus scrofa, frequently than numerically abundant but much smaller cervids like C. axis. Tigers occasionally take rhinoceros and elephant calves but adults are too large for them to kill. These megaherbivores form an enormous proportion of mammalian biomass in the south and south-east Asia but tigers do not take these mammals. Tigers kill prey when encountered which may include prey of smaller size but they seek and kill larger ungulate prey. They usually don’t prefer smaller prey for perhaps the poor return energetically.


The difference between the smallest extant tiger from Sumatra and the largest from India is remarkable when put side to side. The island Male tigers are the size of the largest jaguars. A female Sumatran tiger is the size of a northern male puma. While a tiger is a versatile predator, we should not expect the smaller tiger morph to be as efficient a predator with some large prey types. Neither should we expect larger tigers to be efficient with smaller prey. This prediction is confirmed in a recent study done on tiger and leopard density and food habitat in Thailand. In Huai Kha Khaeng Wildlife Sanctuary it was found that Bos javanicus, Bos frontalis, and  Cervus unicolor were reduced in number greatly, Muntiacus feae was very rare or extinct and Cervus eldi was extinct. Tiger had very large home ranges and was far less in abundance than Leopards which were pretty much abundant. Muntiacus muntjak was the major prey for both leopards and tigers. However, due to the less abundance of M. muntjak leopards were still doing well as they could survive on a mixture of small ungulates, rodents, and other small mammals. On the other hand, tigers were not doing so well.


Bengal Tiger; Courtesy: Sustainability Times

Sumatran Tiger; Courtesy: Dino Animals


As most of the tiger habitats are influenced and changed by human impacts, we are without baselines in assessing the role that tigers play in structuring the communities where they occur. Eisenberg predicts that the removal of a top predator will have cascading effects on the herbivore population with an increase in the guild and number of smaller predators. Tigers keep the prey population in check and thus do not cause a decrease in the food resources available to smaller herbivores. One of the twisting aspects of tigers is that, why don’t tigers kill far more people than they do? This may be due to the variation in the key variables in determining the direction, rate, and mode of the final approach. This variability may be due to a lack of adequate cover and the different attitude and the movement of the prey. Walking in a normal upright position by a person is not an adequate form of attack by the tiger. It is seen that tigers kill people when the latter is sitting rather than standing. Tigers kill rubber tappers who go out at dawn and bend down to make their cuts and grass cutters are who are bending over. They also hunt people who go out at night to relieve themselves. As densities of tigers in protected areas have increased, subadult tigers can be expected to occur more frequently in the edges and more active in daylight, thereby increasing encounters with people engaged in various activities. This sets the stage for an attack.


To sum it up, tigers are known to capture prey of varying sizes and types, hence the prey capture is plastic. In Nepal’s Chitwan National Park, tigers prefer the large ungulates to the smaller ones which give them access to a substantial proportion of the ungulate biomass which is not available to smaller felids. It is a general observation that if the primary prey ungulate of tigers is large the tigers have a larger body as well. The mainland tiger is as large as twice the Sunda Island tiger. This feature may help tigers to hunt down larger ungulates and reduce their dependence on smaller ones. Thereby making them useful for the smaller felids and carnivores. The smaller body size of the Sunda Island tiger may increase the efficiency of capturing the smaller prey that is relatively abundant in rainforest environments. But this does not mean that Sunda tigers don’t hunt large prey, such as Bos, which weighs on average 800 kilos. 


Understanding tiger resource acquisition can be helpful in tiger conservation. The loss of larger prey from a habitat can adversely affect the tiger population in that habitat. Larger tigers will be more vulnerable to starvation compared to the smaller ones. The extirpation of tigers from an area can cause a disbalance in the ungulate population in the area with an increased number of smaller predators, thus, altering the community structure. Also, problems like human killings may come up when individual tigers are excluded from normal prey populations through social processes or when individual tigers become habituated to humans and learn how to capture them when humans and tigers frequently use the same areas.



REFERENCES


[1]- Seidensticker, J. and McDougal, C., 1993. Tiger predatory behaviour, ecology and conservation. Symposium of the zoological society of London., 65, pp.105-125.

[2]- Schaller,G.B.(1967).The Deer And The Tiger:study wildlife India.University of Chicago Press, Chicago & London.

[3]- Sunquist, M. E. (1981). The social organization of tigers (Panthera tigris) in Royal Chitawan National Park, Nepal. Smithsonian Contr. Zool. No. 336: 1-98.



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