The Tiger - a natural history.
The tiger is a charismatic animal featuring in many myths both ancient and modern. A cult has been built around the tiger over its entire historical range. It is now time to see the tiger for what it really is.
The tiger is the largest of all living wild cats with males having a total body length of 106 to 122 inches and weighing in at 175 to 260 kgs. The females are smaller at 95 to 195 inches and weigh about 100 to 175 kgs. They have a shoulder height of approx. 36 to 44 inches. They posses a strong but light skeletal structure with powerful muscles superbly adapted to the life of a predator. Tigers have five front toes and four hind toes with sheathed claws and posses thirty teeth.
Tigers occur in cold temperate zone forests as well as in the hot, humid wet and dry forests of Asia. They can tolerate high ambient temperatures of up to 48C as well as severe cold climates of -35 C. They are however not adapted to arid water scarce environments. They live in altitudes ranging from sea level to 3000 m and have known to have crossed Himalayan passes at 4700m.
Tiger have eyes that are sensitive enough to cope with low light conditions and at the same time are able to function effectively in broad daylight. They are able to discriminate colour and detect details even in poor light conditions. They have binocular vision (eyes in front of the head), which enables them to judge distances, so vital for a predator. Their hearing is sharp with a frequency range of 100 to 200 kHz. The tiger has padded feet which enables it to feel the substrate and avoid dry leaves which if disturbed can scare away prey. Its whiskers allow it to touch and feel objects close to its face thus enabling it to get close to prey in pitch darkness and dense cover. Their sense of smell is however poor. Nevertheless, it does play a central role in communication between tigers. They have a Jacobson’s organ on the roof of their mouth, which is used to test scent. They have scent glands around their cheeks, toes, tails and their ano-genital region. They exude scent mixed with urine and feces.
Tigers live alone with each individual maintaining a fixed territory of their own. As these territories are fiercely defended communication between tigers assumes significance in avoiding conflict. As mentioned earlier scent plays an important role here, especially in demarcating territory. Scent is deposited on the ground from glands on their feet as they walk. It is sprayed mixed with urine on trees and other prominent places at regular intervals. They also rub their cheeks against bushes and trees leaving scent deposits in the process. It is also deposited along with scat (feces) and often combined with urine on the ground. They very often scrape the ground with their hind feet and cover the scat lightly with soil probably to preserve moisture and scent. It also draws attention to the scat by creating a prominent patch of bare soil.
Tigers also use vocal and visual aids in communication. They posses a wide range of calls from loud roars, that can be heard upto five kilometers, and soft moans and groans used for communicating with cubs. The visual aids employed when they meet face to face are facial grimaces, position of ears, and the narrowing and widening of eyes combined with vocalization and twitching of tails.
The other visual signs are created when they rise up on their hind legs and use their front paws to rake claw marks on tree trunks. They also roll on the ground to churn up patterns in the dust or to flatten the grass all around.
Tigers can be classified based on age into the following classes. Cubs- below twelve months, Juveniles- twelve to twenty- four months, Transients-above twenty-four months, dispersing tigers that do not hold stable home ranges or who do not breed, Resident Breeders- above twenty-four months, maintain stable ranges and breed.
Breeding females usually acquire stable home ranges and start breeding at three to four years of age. They manage to hold on to their range for about five to seven years and produce litters of three to four cubs once every two to three years.
Breeding males typically have home ranges that overlap the ranges of several females with the average being about three. They have a significantly shorter tenure of about two to four years.
Tigers have an estrus cycle of about three weeks with the period of heat lasting two to six days. In tropical areas this is not a strongly seasonal activity with no pronounced breeding season. Mating tigers usually associate with each other for two to three days and spend most of the time copulating. They mate with a frequency of over fifty times a day with each copulation lasting fifteen seconds.
Cubs are born after a gestation period of 103 to 110 days; the litter size can range from one to seven with three to four being the norm. Tigers prefer to litter in thick cover, under fallen logs or in rocky crevices. The entire litter is delivered in about ten hours. The cubs are born blind and helpless and the sex ratio at birth is usually equal. Mortality is the highest at this time.
The cubs are nursed on milk for the first two months. After that the mother starts taking them to her kills. Within a year they accompany their mother most of the time.
Cubs develop strong permanent canine teeth at about twelve to eighteen months and are thus potentially able to kill. By this time they also start moving around on their own, staying closer to each other than to their mother but restricting themselves to their mother’s home range.
By two years, their association with their mother and her home range gradually decreases and when their mother is ready to deliver her next litter, she turns aggressive thus forcing them to disperse from the natal range.
Dispersing tigresses usually try to find home ranges close to their mother’s with the mother usually shrinking or shifting her own territory. Dispersing males cover great distances and have to evict resident males to acquire territories.
Natural mortality rates in tigers are quite high. In productive habitats it is estimated as follows: cubs-40%,juveniles-10%,female transients-30%,male transients-35%,breeding females-10% and breeding males-20%.
The size of a tiger’s territory is directly depended on the availability of suitable prey with each adult tiger requiring about 3000 to 3600 kgs of live prey a year. Thus, the availability of prey is one of the dominant factors governing tiger numbers. To save wild tigers it is extremely important to save their prey, a vital point usually missed by the average citizen.
Personal Note
Most of my knowledge on Tigers is due to the patience shown by Dr. Ullas Karanth , both through his scientific papers ( which he very kindly let me have copies ) published books and discussions with him. I like to thank him for taking an interest, tolerating and encouraging me . I am saying this , in my defense ,because I feel that a lot of people may have a difference of opinion on the natural history of Tigers especially based on observation in Parks like Bandhavgarh etc which in my opinion are now closer to the Singapore zoo than to truly wild habitats. Since Nagarhole was Dr. Karanths study area and since I live here I have relied heavily on him. Behaviour is also heavily influenced by the environment in which an animal lives and the same species have shown different behavior patterns in different environments.The basic idea is that one should learn about animals that live in a particular area from studies that have been carried out in the same particular area. In my next post I will discuss the reasons for the co-existance of large predators in high densities in Nagarhole which might come as a shock to some people more used to idea of the the exclusion of leopards from Tiger areas.
